Last Update: 6/17/2025 6:00 PM CDT
Despite mostly/partly sunny skies, strong south westerly low level flow within the arm sector of a low pressure system centered all the way up in northeastern Ontario by Hudson Bay have allowed for highs across the Chicago area to once again blossom into the upper 80's and low 90's. Continued moisture advection in the flow has once again led to dewpoints in the upper 60's and low-mid 70's, resulting in heat indices in the mid-upper 90's. Thus, very muggy, uncomfortably hot conditions have prevailed across northeastern Illinois today. Deep vertical mixing up to at least 850 mb has brought down relatively strong 10-20 mph (gusting up to 25 mph) southwesterly winds to the surface, providing a slight bit of relief from the warm, moist air mass at the surface.
Recent surface observations depict a cold front stretching southwest from the surface low in northeastern Ontario, cutting diagonally across the northern Great Lakes, and central Wisconsin into north central Iowa. Satellite and radar depict convection initiating just ahead of this boundary in southeast Iowa and northeast Missouri. Aided by a few subtle upper level short waves stretching from southeast Nebraska into northwest Illinois, subsequent outflow from this convection will likely initiate more scattered showers and storms across central and northern Illinois as the front slowly drifts southeastward this evening. Recent CAMs generally depict scattered showers and storms spreading across the far northwest suburbs, and Lake county by around 7 pm tonight before more widespread coverage of scattered showers across northeastern Illinois arrives with the cold frontal passage in the midnight-1 am time frame, before slowly dissipating as it pushes off to the east in the 3-4 am time frame. Thunder will likely remain elevated late tonight with the nocturnal boundary layer setting in, so the main risk for surface based convection will be with the early evening storms. The severe threat also looks relatively low with very little deep layer shear, and mid level lapse rates (3-6 km AGL) generally hovering around 6ºC/km, despite MUCAPE around 1,000 J/kg. The main concern with showers and storms tonight is heavy rainfall, with impressively deep column saturation up to ~400 mb, PWATs between 1.5 and 1.75 inches, and 12-hour QPFs by 12Z tomorrow of over an inch in some areas. That being said, given the widely scattered nature of these showers, this looks to be a situation where one area can receive an inch of rainfall, while the next town over may get less than a tenth of an inch. Despite the cold frontal passage, mostly cloudy skies and a heavily saturated atmosphere will limit lows to the upper 60's and low 70's area-wide, with a SSW wind of 5-10 mph.
The primary upper trough will make its way into our area tomorrow, surging northeastward from northeastern Missouri throughout the night, and into northeastern Illinois by early tomorrow afternoon, bringing more chances for showers and storms throughout the day as the attendant surface low passes directly over our area in the early-mid afternoon as well. Tomorrow's setup looks to be much more favorable for severe weather, particularly southeast of the city (also southeast of the surface low) ahead of the low-level jet, where enormous surface based CAPE (2,000-3,000 J/kg), impressive deep-layer shear (~40 knots sfc-6 km shear), and strong convergence on the leading edge of the warm front stretching east from the low will allow for organized supercellular convection early in the afternoon. While some CAMs (particularly the HRRR, and the 3-km NAM to a lesser extent) depict impressive low level shear profiles (30-40 knots of sfc-3km shear) with favorable curvature, others such as the RAP, and the FV3 offer very little directional shear, thus limiting the tornado risk to marginal. The primary mitigating factors for this severe threat are the mid level lapse rates (still struggling to rise above 6ºC/km), and some modest mid level capping indicated by a few CAMs, which will likely prevent all 2,000-3,000 J/kg of CAPE from being accessed. Also, with mostly cloudy skies topping highs out in the upper 70's and low 80's, it remains questionable whether or not the surface will be able to destabilize enough to initiate storms before the surface low (and thus better forcing) shifts to the east in the mid afternoon hours. Regardless of severe weather, expect scattered showers and storms to persist throughout the Chicago area tomorrow afternoon-early evening, with a 5-15 mph southerly wind (gusting up to 25 mph) becoming westerly throughout the day. Between half an inch to an inch of rainfall is expected.
Last Update: 6/18/2025 12:30 AM CDT
Showers and storms will gradually taper off Wednesday evening by around 11 pm as the low pressure system pushes off to the east. We will then be left with mostly cloudy skies, and lows in the low-mid 60's, with a 5-15 mph westerly wind turning northwest overnight. Subsidence should mostly clear cloud cover by the mid morning hours on Thursday as the left side of the upper trough axis shifts overhead. This will lead to mostly sunny skies on Thursday, with highs in the low-mid 80's, and a northwesterly wind at 5-10 mph, shifting west throughout the day.
Upper level ridging looks to take hold across the central CONUS throughout the day on Thursday, and will eventually become amplified as an upper trough digs into the Pacific Northwest this weekend. This will result in mostly sunny/sunny, and dry conditions through the start of next week. A few ripple-like shortwaves dart southeastward out of Wisconsin overnight Thursday into Friday, with a few models (namely the NAM and GFS) depicting scattered showers propagating through far northern Illinois near the Wisconsin border. However, with antecedent subsitive conditions, a relatively dry lower boundary layer, as well as both ensemble guidance (EPS, GEFS, CMCE), and NBM indicating very low PoPs Thursday night, I will leave these scattered showers out of the forecast for that period.
With ridging overhead and low level flow turning south/southwesterly towards the end of the week allowing for impressive WAA, as well as moisture advection, stages will be set for a very hot, humid weekend. Saturday-Monday, highs will likely be in the low-mid 90's, dewpoints in the mid-upper 60's, and lows in the mid-upper 70's, all under sunny skies, and an ever persistent southwesterly wind. Due to the extreme heat, and high dewpoints, heat indicies could climb as high as the low-mid 100's this weekend.
Last Update: 6/11/2025 10:00 PM CDT
With surface high pressure domination to the southeast, weak upper ridging over the central Midwest, as well as a low-mid level thermal ridge passing over our area earlier this afternoon (~20ºC at 850 mb), sunny skies and highs in the low to mid 90's prevailed across the Chicago area today. The relatively weak surface pressure gradient owing to the aforementioned high pressure system to the southeast would normally lead to relatively weak surface winds, but a very dry troposphere ( surface dewpoint depression ~30ºF), along with very deep vertical mixing resulted in breezy 10-15 mph winds gusting to 30 mph.
Tonight, an east-west oriented cold frontal boundary in southern Wisconsin will dip southwards into northern Illinois, before stalling out near the I-88 corridor tomorrow morning. Meanwhile, a series of low amplitude upper level waves will work their way ESE through south central Wisconsin and into central Michigan throughout the night, pushing current scattered showers and storms brewing along the baroclinic zone in northeast Iowa and central Wisconsin eastwards into southern Wisconsin, far northern Illinois, and Lake Michigan. These showers and storms should remain far north of the Chicago area near the Wisconsin border throughout the night due to the aforementioned locally dry troposphere, though with the cold front sagging southwards, expect winds to shift to the northeast (5-10 mph, gusting to 15 mph) overnight. Otherwise, relatively seasonable conditions should prevail tonight, with partly cloudy skies, and lows in the mid-upper 60's (lower 60's to the far northwest behind the cold front).
Tomorrow, the northeasterly lake breeze (8-14 mph, gusting to 20 mph) augmenting the recently passed cold front will keep lakeside highs to the low to mid 70's, while inland areas will still be able to reach the mid-upper 80's, all under mostly sunny skies. Humidity levels will also be noticeably higher tomorrow behind the front, with dew points climbing to the low-mid 60's. With upper level ridging still remaining dominant, and an impressively deep well mixed layer, with little to no moisture between ~800 mb and ~400 mb based on latest soundings, our area should remain largely dry tomorrow. However, as the cold front continues to sagg southwestward into interior north central Illinois throughout the day, dewpoints in the low-mid 60's along the boundary, in addition to impressive vertical mixing eroding the cap, and increasing low level lapse rates, may allow for some isolated diurnally driven storms far southwest of the Chicago area. A still 5-15 mph post frontal northeasterly wind will allow temperatures to sink into the upper 60's shortly after sunset.
Skies will then become cloudy overnight tomorrow night as a mid-upper level low pressure system slowly crawls its way northeastward from the Ozarks into southwestern Illinois by early Friday afternoon. This should dampen lows to the low-mid 60's tomorrow night (upper 50's in far northwest suburbs).
The aforementioned mid-upper level low will gradually weaken into a wave Friday afternoon as it slowly pushes eastward through the southern Illinois Ohio River Valley into Saturday. Models are in pretty good agreement that our area will be swept up in the far NNW periphery of the precipitation field from this system throughout the day, however, there continues to be disagreement in the exact coverage, and intensity of these showers and storms. GFS, RAP, and HRRR model guidance depict more of a scattered coverage of showers, generally on the southeastern half of the metro throughout the day, with the HRRR in particular advertising a higher coverage of thunderstorms later in the afternoon mainly southeast of the I-55 corridor. Meanwhile, the NAM and 3-km NAM depict widespread coverage of showers and storms throughout northeastern Illinois everywhere south of Lake county, with similar advertisements of thunderstorms southeast of I-55 in the afternoon to the HRRR, though noticeably much earlier in the afternoon (around 12-2 pm). Thus, I will put a 60% chance (20% in the early morning) of scattered showers throughout the day south of Lake county, then a 50% chance of scattered showers and storms after 2 pm, mainly southeast of I-55. Thanks to cloudy skies and rain, expect highs ranging from the mid 70's to around 80 throughout the area on Friday (lower 70's in the far northwest suburbs due to a lake breeze), with a southeasterly wind around 10 mph.
Lows will be relatively mild in the mid 60's Friday night under mostly cloudy skies in the wake of earlier afternoon/evening showers and storms, and an easterly wind between 5-10 mph, shifting northeasterly throughout the night.
Saturday will be another cloudy, cool, and possibly rainy day in the afternoon as a northern stream low amplitude shortwave dives southeastward through Wisconsin, bringing a (~40%) chance of scattered showers and storms throughout our area in the afternoon. Highs will be dampened by a northeasterly lake breeze (around 10-15 mph), causing lakeside locales to top out between the upper 60's and low 70's, while further inland areas will make it to the upper 70's, all under mostly cloudy skies.
High pressure will dip southwards from Canada on the second half of the weekend, leading to drier conditions on Sunday and Monday, albeit still cloudy (mostly cloudy nights, partly/mostly sunny days), and seasonably cool (upper 50's lows, upper 60's/low 70's highs).
Hot and humid conditions look to be on tap for the middle part of next week courtesy of broad-scale upper ridging throughout the CONUS east of the Rockies. A few ripple-like shortwave disturbances pass through the flow over our area in the Tuesday-Wednesday timeframe, but these disturbances will need to be reexamined as more model guidance comes in later this week.
Last Update: 6/9/2025 6:30 PM CDT
Temperatures throughout the Chicago area should fall back into the mid-upper 60's by sunset under mostly sunny skies with the recent cold frontal passage earlier this afternoon. The passage of an upper level low over the Michigan UP atop its associated surface low, and the resultant pressure falls in our area have led to breezy 20 mph sustained westerly winds, and gusts up to 35 mph. These winds will gradually ease to 10-15 mph (gusting up to 25 mph) this evening as the boundary layer decouples from the upper level flow, and then 5-10 mph (gusting up to 20 mph) overnight as the low pressure system and parent trough gradually push off to the northeast into Canada. Showers and storms that popped up in northwestern parts of our area earlier this afternoon with the frontal passage have since pushed well off to the east into central Michigan and northeastern Indiana. Trailing scattered showers behind the front look to remain off to our north in Wisconsin thanks to better synoptic forcing and upper level vorticity in closer proximity to the upper level low.
Tonight, as the aforementioned upper trough pushes off to the northeast, surface ridging will build into the lower Mississippi River Valley, which should help maintain mostly clear skies, and lows in the low-mid 50's areawide. Despite temperatures cooling close to the dewpoint in some areas tonight, sustained winds up to 10 mph, and gusts up to 20 mph should be enough to advert any patchy fog development.
As mid-upper level flow turns to the northwest with the northeasterly departure of the upper trough, Canadian wildfire smoke will once again seep into our area throughout the night tonight, and into the day tomorrow. While high-res smoke guidance from the HRRR has tended to over-do near surface smoke concentrations as of late, latest sounding data from the HRRR, 3-km NAM, and RAP each depict a relatively deep boundary layer expanding to above 850 mb tomorrow afternoon. Therefore, it seems reasonable to suspect that some of the higher smoke concentrations forecasted by the HRRR (over 200 mg/m²) will mix down to the surface, and lead to patchy smoke/haze development throughout the afternoon. Despite the haze, however, surface high pressure to our south will still allow for mostly sunny skies, and highs in the mid-upper 70's areawide, with a 10-15 mph westerly wind gusting up to 20 mph.
Tomorrow night, our area will become sandwiched in between mid-upper level ridging building into the southeastern quadrant of the CONUS, and relatively zonal flow across the Great Lakes to our north. Consequently, Tuesday's local smoke concentrations should push off to the east, and the zonal flow to our north should keep any more wildfire smoke blowing from the Canadian Plains well north of us in northern Wisconsin and Michigan through the day on Wednesday. Southwesterly WAA will keep lows in the mid 60's tomorrow night, despite mostly clear skies, and southwesterly surface winds around 10 mph, gusting up to 15 mph.
The upper ridging pattern will likely result in much warmer conditions in our area on Wednesday, with 850 mph temperatures peaking at 18ºC according to the 18Z NAM (18Z GFS at 17ºC), and NAM 925 mb temperatures peaking around 25ºC (~77ºF). With sunny skies, and surface ridging still to our southeast allowing for robust diurnal heating, highs on Wednesday will easily reach the upper 80's, and possibly low 90's areawide, with a 10-15 mph southwesterly wind gusting up to 20 mph.
Last Update: 6/9/2025 11:40 PM CDT
Wednesday afternoon, surface high pressure will slowly build southward into eastern Manitoba and western Ontario, leading to surface pressure falls across the great plains, and the development of a baroclinic zone stretching along a line of latitude roughly extending from the northern border of Illinois, through central Iowa, and southwest through Nebraska. This boundary, along with a few weak mid-upper level disturbances moving atop the zone in what otherwise appears to be zonal flow, will serve as the impetus for periodic chances of showers and storms for our area through the end of the work week. While it is possible that some of these storms may be somewhat strong with damaging winds and/or hail, guidance remains very inconsistent with various parameters such as CAPE, degree of instability, and timing of the storms, so potential for severe weather will need to be reevaluated later in the week. As for a few general notes, most mid-long range guidance (ECMWF, GFS, NAM, GDPS) depicts the focus of shower and storm development in our vicinity being primarily in northern Illinois and southern Wisconsin until around Thursday evening when convection will spread throughout the rest of our area, persisting through this weekend. Secondly, most guidance depicts relatively weak speed and directional shear for these storms through at least Friday morning, signaling that even if strong storms were to materialize, they would likely be short lived and fizzle out quickly as they rain into their updrafts. Considering all these uncertainties at play, I will stick with a general 30% PoP for Wednesday evening through late Thursday afternoon (primarily for the far northwest suburbs), then bump PoPs up to 50% for Thursday evening through Saturday due to wider aerial coverage of precipitation from guidance.
With all the chances for showers and storms in the latter half of the week, expect mostly cloudy/partly sunny skies, and relatively seasonable temperatures with highs ranging from the upper 70's to low 80's, and lows in the low-mid 60's.
Looking ahead to the first half of next week, ensemble guidance depicts very hot, humid conditions on the horizon. Of course, this brings with it greater potential for severe weather, so stay tuned for further updates.
Last Update: 6/7/2025 6:00 PM CDT
Recent satellite and radar observations depict a relatively large cluster of showers and storms ahead of a surface low, pushing northeast and crossing the Mississippi River in northeastern Missouri into western Illinois. A warm front stretching ENE from the low delineates the northern boundary of shower/storm coverage, and looks to be slowly meandering northwards around the I-80 corridor. As a result, antecedent quiet, mostly sunny conditions with highs area wide in the low to mid 70's, and a few plumes of wildfire smoke trapped in the lower boundary layer creating some instances of haze, will soon be overrun by scattered showers early this evening, eventually becoming widespread later tonight. Despite minimal MUCAPE generally less than 100 J/kg (may hear a few rumbles aloft), increasing convergence along the front as the low pushes into central Illinois, in conjunction with relatively saturated thermodynamic profiles (PWATs up to 1.5"), favorable lapse rates (generally near or greater than moist adiabatic), and slow storm motion (sfc-3 km mean wind less than 20 knots), localized instances of heavy rainfall will be likely throughout the Chicago area as the bulk of the shower cluster makes its way over northeastern Illinois later this evening. Remnants of a weaker circulation currently brewing scattered showers across central Iowa look to merge just behind the aforementioned cluster of showers as it pushes eastwards into northern Illinois later tonight, which may result in lingering scattered showers until around 3-4 am.
After showers pass, relatively calm 5-10 mph ENE winds, and lingering low level moisture from the rainfall within a nocturnal boundary layer may lead to some patchy fog developing, primarily in northwestern Illinois, along the lake, and in some inland areas southeast of the city. Along with patchy fog and ENE winds at 5-10 mph, expect cloudy skies tonight, with lows in the lower 60's (upper 50's to the far NW where clouds clear).
After a relatively mild (mid-upper 60's mid-morning temperatures), calm, and mostly sunny start to the day tomorrow, an upper level closed low will gradually push southeastward from southern Manitoba into the upper midwest, with the leading edge and associated ascent from the mid level trough pushing through northwestern Illinois throughout the afternoon. As the adjacent surface low pressure system pushes east into Ontario, an associated coldfront stretching SSW through the Great Lakes into the Mississippi River Valley will pass over our area later tomorrow afternoon (4-6 pm time frame). Ahead of the front, scattered showers and storms will develop early tomorrow afternoon, primarily in the far northwest suburbs. As the mid level trough and associated vorticity plumes build into our area after the frontal passage, expect continued coverage of scattered showers through around 1-2 am Monday morning. Latest high-res guidance depicts substantial saturation throughout the thermodynamic profiles along the front, as well as impressive surface based CAPE greater than 1200 J/kg, all favoring strong to damaging convective winds greater than 40 mph, as well as small hail up to 1.5" in diameter. However, minimal frontal convergence, relatively weak synoptic forcing along the front (front will be far to the southeast of the parent upper level trough), a weak thermal gradient, and lack of deep layer shear will prove to be massive limiting factors for the lifetime, coverage, and intensity of these storms. With all said and done, storms that initiate tomorrow afternoon will likely be single-celled, short lived isolated-scattered pop-up storms with some limited potential for convectively enhanced wind gusts (40-50 mph) and small hail (less than 1.5", about pea-sized). High temperatures ahead of the front will likely reach the upper 70's and low 80's before clouds roll in throughout the afternoon. With a relatively calm ENE wind at 5 mph in the morning, winds will turn to the WSW in the afternoon and increase to around 10 mph, gusting up to 20 mph.
After showers push off to the east overnight tomorrow, the post cold frontal air mass will allow lows to drop down to the mid 50's throughout the area, with mostly cloudy skies becoming mostly clear by dawn, and a WSW wind 5-10 mph gusting up to 15 mph.
Last Update: 6/3/2025 6:10 PM CDT
Persistent SSW WAA and mostly sunny skies that have allowed for strong diabatic heating resulted in most locales reaching highs in the upper 80's and lower 90's earlier this afternoon. Since then, a patch of convection along a SSW low level jet moved across most of the northern and western portions of the Chicago area, which has left cloudier skies and slightly cooler temperatures in the mid 80's in its wake. Breezy SSW winds of 20 mph and gusts of 30-35 mph will continue this evening into the overnight hours as the surface pressure gradient ramps up due to an approaching cold front stretching from Hudson Bay SW through Wisconsin, Iowa, and northern Missouri, all the way down through the Oklahoma panhandle. A sprawling MCS has developed along the front in northeastern Missouri and continues to grow upscale as it moves northeast into west central Illinois due to diurnally driven instability, along with WAA, creating an environment with up to 3,000 J/kg of MUCAPE.
This system will gradually weaken as it makes its way toward northeastern Illinois and the Chicago area in the 8-11 pm time frame due to weakening instability and increasing CIN (~6.5°C/km MAX 2-6 km AGL lapse rates, ~500 J/kg MUCAPE, and -50 to -100 J/kg MLCIN based off 22Z RAP mesoanalysis). With these latest observations being so close to sunset, it is unlikely that diabatic heating will be able to overcome convective inhibition to initiate strong surface based storms through most of our area, although we may see a few elevated rumbles and scattered showers as the MCS passes to our northwest. However, areas north and west of Cook county may see a few instances of strong thunderstorms and convectively driven damaging winds due to higher CAPE and lower CIN. May even see a brief funnel cloud or two embedded within the MCS further north towards the Wisconsin border due to 30-40 knots of low-mid level (sfc-3km) shear, but this potential will be limited by weakening instability with northern extent.
Last Update: 6/3/2025 10:30 PM CDT
With the initial MCS having moved off to the northeast, a lingering stream of precipitation behind the MCS will persist throughout the night to the northwest of Chicago as the aforementioned cold front slowly moves east into Illinois. Showers and storms will eventually make their way over the city and south suburbs by the 3-4 am time frame. CAA with the cold frontal passage in the mid morning hours will nullify any further thunderstorm chances (except for areas ahead of the cold front far south of I-80). However, lingering scattered showers will likely persist through late tomorrow night, primarily south and east of the city (northwest areas should clear by early tomorrow afternoon) as the front sags into the Ohio River Valley. Due to most of the Chicago area remaining in the warm sector tonight, lows will only make it down to the low 60's, with wind gusts of 30+ mph persisting into the morning.
Once the cold front passes, winds will ease and turn off the lake as the surface low fizzles out and passes over our area. This will lead to a cloudy, rainy, and seasonably cool day with high temperatures ranging from the upper 60's to the far northwest of the city (where clouds will clear in the afternoon) to the upper 50's to the southeast, as well as the lakefront. Despite the clearing to the northwest, latest HRRR smoke guidance has indicated that Canadian Wildfire smoke will surge to the southeast from Wisconsin behind the anafrontal precipitation, which may lead to hazy conditions at the surface through at least Thursday morning in these areas.
Once precipitation ceases tomorrow night, relatively seasonable conditions should return, with lows ranging from the low 50's to the northwest under partly cloudy skies to mid 50's to the southeast under mostly cloudy skies.
High pressure will move into the Great Lakes/Michigan UP by Thursday morning, resulting in mostly sunny skies and highs in the low 70's (mid 60's by the lake due to the lake breeze).
Thursday evening, a weak mid-upper level wave originating from a remnant upper low in the southwest CONUS will spawn a surface low in southwest Kansas just north of the Oklahoma panhandle. This will gradually move to the ENE along the stalled out remnants of Wednesday's cold front and into central Illinois by Friday afternoon. GFS and NAM guidance indicate our area getting clipped by a few scattered showers on the far northwest periphery of this low late Friday afternoon into Friday evening. Though, other models such as the Canadian (GDPS) and European (ECMWF) remain dry. Even ensemble guidance remains uncertain, with GEFS 6 hour PoP>1" at ~30% for Friday evening, while EPS and CMCE remain relatively dry. Due to this uncertainty, along with the fact that we're still 4 days out, I will stick with NBM PoPs for a 30% chance of scattered showers late Friday afternoon into Friday evening. Slightly cloudier and cooler conditions will prevail Thursday night and Friday with lows in the low-mid 50's, and highs in the upper 60's and low 70's (cooler near the lake), all under mostly cloudy/partly sunny skies.
After Friday's low pressure system exits to the east, high pressure will move into the upper Mississippi River Valley, with mid 50's lows Friday night under partly cloudy skies, and highs around 70 Saturday under mostly sunny skies.
Last Update: 6/1/2025 4:50 PM CDT
Surface high over southern Lake Michigan has resulted in a strong temperature gradient over northeastern Illinois due to a persistent ENE lake breeze around 10 mph. Consequently, most lakeside locales have topped out in the low-mid 60's, while locations further inland have made it to the low-mid 70's. The main weather concern for the next several days is the Canadian wildfire smoke in southeastern Manitoba riding NNW upper level flow STEward into the upper Midwest Mississippi River Valley, along the leading edge of an upper level ridge taking shape over most of the western 2/3 of the CONUS. Despite clear skies and dry surface conditions over Northern Illinois due to the aforementioned surface high allowing for robust diurnal mixing, have yet to see any major visibility obstructions due to smoke on surface observations, so as for now it appears as though smoke impacts will remain far to the WNW until the upper ridge progresses eastward and flow turns WNW tomorrow afternoon.
As for tonight, mostly clear skies and relatively calm surface winds will prevail as the surface high slowly meanders ESE throughout the night, causing ENE winds to gradually veer to the south. This setup will allow for a relatively strong radiative cooling regime to drop lows to the upper 40's and low-mid 50's areawide. With dew points topping out in the mid-upper 40's along the Northern Illinois lakeshore, may see some dew/patchy fog formation in these areas throughout the overnight hours. However, the air will remain much too dry elsewhere to warrant an areawide fog forecast.
Tomorrow will be another relatively sunny day throughout the area, with winds turning to the south allowing for impressive WAA. This, combined with strong diurnal mixing under sunny skies, will allow highs to climb to the mid-upper 80's areawide. On the topic of diurnal mixing, with the upper level ridge over the western 2/3 of the CONUS pushing eastwards throughout the night, upper level flow will turn WNW by tomorrow afternoon, thus allowing for Canadian wildfire smoke to seep into our area. The resultant vertical mixing may allow for patchy smoke to sink down to the surface, which would likely cause some minor visibility obstruction and haze on what would otherwise be a clear day. Southerly winds may be a bit stronger tomorrow due to an increasing surface pressure gradient as a result of low pressure building on the plains ahead of the next system. Therefore, expect relatively light 5-10 mph winds to increase to 10-15 mph later in the afternoon.
Monday night, as a result of increasing cloud cover (Partly Cloudy), and strong southerly WAA, lows will be very mild in the mid 60's throughout the area, with a 10-15 mph southerly wind gusting up to 20 mph.
Last Update: 5/19/2025 6:50 PM CDT
Relatively breezy and cool conditions will persist throughout the rest of this evening across the Chicago area with a mid 1030's surface high over the Hudson Bay, and an increasing surface pressure gradient in our area in response to deepening low pressure across the Great Plains leading to a cool northeasterly lake wind of 10-15 mph, gusting to 20 mph. This has limited high temperatures to the upper 40's, while areas further inland have reached the mid-upper 50's. Skies have remained mostly cloudy throughout the day due to a mid latitude cyclone and its parent trough slowly pushing east from the high plains, with the leading band of cloud cover driven by broad synoptic ascent arcing from central Indiana north into Lake Michigan, then WNW into the upper peninsula and northern Minnesota. Shallow plumes of mid-level moisture and marginal MUCAPE resulted in weak bands of showers and storms popping up across west central Illinois earlier this afternoon, though they gradually fizzled out as they moved east due to the drier low-mid level air mass in place in northern and eastern Illinois.
Aided by a mid level shortwave pushing NNE out of Missouri later this evening, the warm front currently stretching ESE from the surface low in northeastern Kansas through southern Illinois into eastern Tennessee will gradually work its way northwards into north central Illinois throughout the night. Increasing southwesterly synoptic ascent ahead of the front associated with this wave, along with increasing positive vorticity advection and diffluence ahead of the front will result in widespread coverage of showers throughout northeastern Illinois through early tomorrow afternoon. Thunderstorm chances look to be out of the question with this system, with lapse rates generally below 7 °C/km, and negligible CAPE, which can likely be attributed to the relatively cool air mass in place over our area, in addition to evaporative cooling that will come with any rainfall. Despite meager instability, the depth of moisture being advected into our area ahead of the warm front will likely bring periods of soaking rainfall, with PWATS greater than 1.5" in the southwestern regions of the Chicago metro. This combination of marginal instability and heavy amounts of moisture will result in rainfall rates potentially exceeding 0.2" inches/hour in the hardest hit areas. Most model guidance depicts total QPF between 1 to 2 inches by Thursday afternoon after rain chances have ceased.
As the main swath of widespread rainfall exits to the north of our area early tomorrow afternoon, the warm front should stall out somewhere south of I-80 and north of the Kankakee River, due to the colder air mass in place over our area, along with strong easterly surface winds in response to the surface low tracking into northwest Illinois near Davenport. This will allow for continued coverage of scattered showers throughout northern Illinois, with potentially a few elevated thunderstorms as mid level lapse rates increase tomorrow afternoon. Best chances for strong thunderstorms remain farther south of our area near the warm frontal boundary, where sunnier skies and consequential solar insolation may increase low level instability enough to allow for surfaced based storms. This will be limited by meager low level shear, as well as persistent low level capping.
Heading into tomorrow night, expect continued coverage of light scattered showers through Wednesday morning as a mid level shortwave pushes east through central Illinois. With the surface low approaching northwestern Illinois tomorrow morning, gradually increasing the surface pressure gradient, expect breezy easterly sustained winds of 15-25 mph, and gusts up to 40 mph to persist through tomorrow evening. As a result, high temperatures tomorrow will be limited in the northwest suburbs near the lake to the upper 40's and low 50's, while areas of the south of the city will reach the mid-upper 50's, and possibly 60's south of I-80. Persistent cloud cover should keep lows to the upper 40's and low 50's areawide for the next several nights.
Winds will shift to the WNW overnight tomorrow night, and along with persistent cloud cover and shower coverage, highs on Wednesday will be limited to the low-mid 50's areawide. The closed upper low will elongate as it gradually meanders eastward from the upper Midwest into the Great Lakes throughout the afternoon on Wednesday, sending another weak mid-level shortwave southeastward across northwestern Illinois Wednesday evening. This may result in periods of light scattered showers primarily in the northern half of the Chicago metro Wednesday night through Thursday morning, and will also maintain the relatively cloudy and cool conditions.
Guidance starts to get very inconsistent with the progression of the Great Lakes upper low system after Thursday, although EPS and GEFS ensembles generally indicated that upper level flow should remain approximately geostrophic through the first part of the weekend, diminishing chances for any precipitation. NBM also indicates generally dry conditions, although still on the cool side, with highs topping out in the low 60's and lows in the mid-upper 40's, with northerly winds and partly cloudy/mostly sunny skies.
Last Update: 5/15/2025 4:40 PM CDT
The warm front that passed over our area from the south early this morning has since stalled out near the lakeshore the northern Illinois border. Impressive diurnal heating and robust southerly WAA under mostly sunny skies have allowed for record highs in the low-mid 90's throughout the Chicago area. Gulf moisture advection within the warm sector has also allowed for dewpoints to soar into the mid-upper 60's. When combined with an increasing surface pressure gradient ahead of the low pressure system in the upper Midwest allowing breezy winds up to 25 mph and gusts over 30 mph, this afternoon has shaped up to be an abnormally hot, muggy, and breezy one for mid May.
Diurnal mixing has allowed for low level moisture to mix out throughout most of western Illinois, resulting in stronger capping. However, strong synoptic ascent associated with an approaching hybrid cold front/dry line feature stretching southward from a triple point in northeastern Iowa has resulted in cumulus development in northern and western Illinois near the Mississippi River. If forcing along the front manages to break the cap, an impressive CAPE of 4,000+ J/kg, 40+ knots of deep layer shear, and surface-3 km lapse rates over 8°C/km will allow for some explosive severe thunderstorm development throughout our area this evening. With a deep layer shear vector perpendicular to the hybrid cold front/dry line, storms will likely develop into discrete supercells as they approach our area, with possibly locally damaging winds of 60+ mph and hail up to tennis ball size (2.5-2.7 inches). As SSW surface winds associated with the cold front/dry line come into contact with with stalled warm frontal boundary by the lake, rapid surface pressure falls will lead to a low level jet developing primarily near and east of the I-57 corridor into NW Indiana, where widespread sustained winds up to 25 mph and gusts over 35 mph will likely persist into the evening hours. While the tornado threat will remain marginal throughout the Chicago area due to a well mixed boundary layer and high LCL heights, the arrival of this low level jet early this evening may ramp up low level shear enough to cause a few spin-ups, primarily in northwest Indiana.
Last Update: 5/6/2025 7:00 PM CDT
Relatively quiet and calm conditions have prevailed throughout the area today, with an upper level ridging pattern developing across the northern Great Plains and upper Midwest in the wake of the eastward exit of the closed upper low that had impacted us this past weekend. Skies have remained mostly sunny, save for a few diurnal cumulus around the lakeshore in northern Illinois courtesy of strong vertical mixing and high surface dew points. The ridging pattern, along with relatively clear skies have allowed highs to surge into the mid-upper 70's across most of the area.
Our area will remain sandwiched between a broad area of lower pressure across the northeastern Great Lakes into Quebec, another area of low pressure in the southwestern Great Plains/Colorado, and a strong mid 1030's mb surface high slowly building southeastward from the Hudson Bay throughout the overnight hours. This, in combination with upper ridging will result in calm 5-10 mph winds, and mostly clear skies prevailing through the overnight hours, with subsidence managing to keep lows relatively mild in the mid 50's (low 50's in the NW suburbs).
Over the next several days, a broad upper ridging pattern will develop in the polar jet stretching from the Pacific northwest to the western Great Lakes, which will work to block the subtropical jet further south in northern Mexico and the Gulf Coast, along with any significant low pressure systems associated with it. This will result in relatively calm and clear conditions for the rest of the week into this weekend.
The only exception to this pattern is a backdoor cold front projected to hit our area in the mid morning hours tomorrow as the surface high currently in Hudson Bay drips southeast, and a strong northeasterly surface wind comes off the lake. This will create a sharp temperature gradient across the Chicago metro, with far northwestern suburbs only managing highs in the lower 60's, while areas further south and inland will hit the upper 60's and low 70's, all in the mid-late morning hours. Then, the backdoor front will send temperatures plummeting through the 50's throughout the afternoon, with most areas around the lake ending up in the mid-upper 40's by sunset (low 50's further inland). The sharp temperature drop will be accompanied by breezy winds of 15-20 mph, gusts of 35+ mph, along with increasing cloud cover throughout the afternoon. Despite the increase in cloud cover the atmosphere will remain much too dry for any precipitation chances, with all afternoon showers associated with the frontal passage confined to the western Illinois Mississippi River Valley, and Iowa.
Cloudy and breezy conditions will persist behind the front through the afternoon on Thursday with sustained winds of 15-20 mph eventually easing to 10-15 mph, and 25+ mph gusts calming to 20+ mph by Thursday morning. Despite the mostly cloudy skies forecasted for tomorrow night, substantial CAA behind the front will drop lows to the mid-upper 40's across most of the area (lower 40's in the far NW suburbs). Skies will gradually clear throughout the morning on Thursday, though CAA will still limit highs to the mid-upper 50's (lower 50's to the far NW), with the lake breeze once again dropping lakeside temperatures down to the mid-upper 40's by sunset (lower 50's inland).
Clear skies and weak winds Thursday night will allow for efficient radiative cooling, resulting in lows in the low 40's across the area (upper 30's to the NW). Similarly, sunny skies on Friday will result in substantial radiative heating, and highs ranging from the upper 50's to low 60's, however the persistent lake breeze will still keep lakeside locales 5-10 degrees cooler.
Long range guidance, as well as ensemble guidance suggest a persistence of the upper ridging pattern from the polar jet across the Great Lakes and upper Midwest. This will result in a gradual warm up throughout the weekend, with conditions likely remaining dry into next week.
Last Update: 5/1/2025 6:40 PM CDT
The surface low and associated scattered showers will continue to push off to the ENE through northern Indiana throughout the rest of the evening. Temperatures should continue to fall to around 60 by sunset in the wake of the cold frontal passage earlier this afternoon. Breezy winds of 15-20 mph will also continue to ease to around 10-15 mph this evening as the surface pressure gradient weakens.
A weak mid level wave currently producing showers across eastern Minnesota will swing cyclonically around the Great Lakes mid level low this evening, bringing chances of scattered showers throughout our area this evening (~30%) into early tomorrow morning (~50%). Aside from a few elevated rumbles in the early morning hours, a stable nocturnal boundary layer and unfavorable mid level lapse rates should keep the area clear of any thunderstorms overnight. Low level moisture should keep skies cloudy throughout the night, though a northwesterly wind gradually turning northeasterly by midnight should keep lows down to the mid to upper 40's across most of the area, with lower 40's near the Wisconsin border.
After scattered showers clear the area early tomorrow morning, conditions will remain relatively dry under partly sunny skies. However, evaporative cooling at the surface combined with a northerly wind will limit highs to the low 60's inland, and mid to upper 50's near the lake courtesy of a northeasterly wind shift in the early afternoon. Another mid-upper trough will approach from Iowa tomorrow afternoon-evening, bringing with it some slight chances (~20%) of scattered showers late tomorrow afternoon into the early evening hours.
Said upper trough will pinch off into a closed upper level low early tomorrow evening. Guidance is still in disagreement on how this low will track through the area, which brings with it considerable uncertainty for the precipitation forecast for this weekend. The GFS/RAP/HRRR models depict a more northerly track for the upper low through central Illinois on Saturday, before stalling out near the Ohio River Valley in southern Indiana by early Sunday morning. This track brings better chances of widespread precipitation across our area Friday night through early Saturday afternoon. Meanwhile, the NAM/Canadian/European/UK models depict a slow, more southerly track of the upper low through Missouri Saturday afternoon before ending up in the southern Illinois Ohio River Valley on Sunday morning. This track remains mostly dry Friday night through Saturday.
The models are in better agreement that widespread showers will pop up early Sunday morning in the southern and eastern parts of the Chicago area, pushing northwest and eventually coming up on the Wisconsin border by sunset Sunday evening. We may see a few scattered showers (20% PoP) Friday night, but due to a slight majority of model guidance, as well as the NBM remaining largely dry on Saturday, I will hold off on forecasting showers for that period. Better model agreement for Sunday will result in 60% PoP throughout the day, mostly after 11 am. Precipitation chances aside, the weekend looks to be relatively cool and cloudy, with lows in the low-mid 40's, and highs in the low-mid 50's, with lakeside locales likely topping out in the mid-upper 40's due to a persistent northeasterly lake breeze.
With a surface low likely tracking somewhere to our south and east through the Ohio River Valley, expect breezy conditions throughout the weekend, with sustained winds of 10-20 mph, and gusts of 25-30 mph. The low will weaken before lifting northwards on Monday, bringing slightly lower chances of precipitation (~40%) to our area late Sunday night into early Monday afternoon. Highs will also be slightly warmer Monday with lower 50's inland, and low-mid 50's lakeside. Seasonable weather will finally return on Tuesday after the system departs to the east, with mostly sunny skies and highs around 70 (still cooler near the lake).
Last Update: 4/29/2025 7:20 PM CDT
Recent observations depict the cold front that passed over our area early this afternoon stretching southwestard from a low in south central Quebec, extending just north of the Ohio river valley southwest into the Texas panhandle. Consequently, winds should continue to ease into the overnight hours as said low pressure system moves east into the Atlantic, and a surface high builds into the upper Midwest.
Northwesterly winds across most of the area will continue to allow temperatures to drop to the lower 60's by sunset, with lakeside locales south of the lake potentially experiencing an even sharper drop to the mid 50's as winds turn to the northeast off the lake. Tonight, partly cloudy skies and easing surface winds will allow radiative cooling to drop lows to the mid 40's near and south of the city, with lower 40's to the northwest towards the Wisconsin border.
Early Wednesday morning, an upper level trough will eject from the desert southwest onto the southern Great Plains, gradually pushing northeastward across the Mississippi River Valley and into the Ohio River Valley by Thursday afternoon. A surface low will then develop along the stalled cold front around the Oklahoma panhandle. In response to gradually deepening low pressure across the Great Plains in the wake of the upper Midwest surface high exiting to our northeast, winds will turn to the east by the morning hours on Wednesday. A warm front stretching east across the Ohio River Valley from the aforementioned low will gradually push northward throughout the day, eventually making its way into our area by the evening.
Considerable synoptic ascent from southerly WAA bringing substantial Gulf moisture into our area will result in periods of showers Wednesday afternoon through Friday. Severe weather looks to be unlikely with this system, with at most 20 to 30 knots of surface-3km shear, thus preventing widespread severe convective organization. Thunderstorm threat also doesn't look to be a concern Wednesday afternoon through early evening, with a capped lower boundary layer, relatively meager mid-level instability, and thus little to no MUCAPE.
Steepening lapse rates Wednesday night will allow MUCAPE to rise to around 500 J/Kg, and with stronger forcing arriving with the low passing overhead late Thursday morning - afternoon, along with the erosion of the inversion in the lower boundary layer, expect much higher chances for widespread showers and thunderstorms Wednesday night through Thursday night. Residual moisture and weak ascent may allow for some scattered showers to persist into Friday morning, along with a few potential thunderstorms later Friday afternoon as a northern stream shortwave phases with the previous upper trough from the southwest, and the system slowly exits to the east by Friday night.
While the severe threat looks to be out of the question with this upcoming pattern, enormous amounts of moisture advection from the Gulf will likely result in some soaking rainfall between Wednesday night and Thursday night. Latest model guidance projects up to 1.5" of precipitable water Wednesday night, and national blend depicts QPF of around 3 quarters of an inch by sunset Thursday evening, with EPS showing parts of the Chicago area with up to 60% chance of QPF greater than 1" for the same time period. Fortunately, river levels and soil moisture are low enough to advert any threat of widespread flooding, aside from some ponding in low level and poorly drained areas.
Temperatures should remain relatively seasonable the next several days, with highs in the upper 60's, and lows in the upper 40's to low 50's. However, an easterly lake breeze tomorrow will likely hold areas along the western shoreline to the mid to upper 50's.
Skies will clear up this weekend as the pair of upper shortwaves exit to the east, and surface high pressure builds into the upper Midwest. As a result, surface winds will turn to the northwest, allowing for slightly cooler, yet still seasonable temperatures for this weekend.
Last Update: 4/25/2025 11:50 PM CDT
The low pressure system responsible for the period of showers and storms earlier this afternoon has since pushed off to the east into southern Michigan and Lake Erie, stretching to the south and west into the Ohio River Valley. With this low pressure center having deepened slightly throughout the afternoon, its attendant cold front having pushed to our south and stalled out near the Ohio River Valley, as well as a surface high building into the upper Midwest, the resultant increase in the local surface pressure gradient will allow breezy northerly winds of 15-20 mph to continue throughout the night, with gusts regularly exceeding 30 mph. An inversion layer near the surface will prevent strong mid-level flow from mixing downward, thus adverting advisory level winds for tonight.
Higher clouds have since exited to our east, but lingering low level stratus will keep skies mostly cloudy tonight, before eventually clearing throughout the day tomorrow. With breezy northerlies tonight expect lows to drop to the lower 40's across most of the area, with upper 30's even possible further north into Lake county near the Wisconsin border.
Tomorrow, the center of high pressure currently in the upper Midwest will push east into the Great Lakes, which should help to clear skies out throughout the afternoon. Despite the clearing skies, the persistent NNE lake breeze will continue throughout the day, setting up a rather sharp zonal temperature gradient throughout the area. Lakeside areas will top out in the upper 40's, with south suburbs reaching the low 50's, and far western suburbs potentially hitting the mid 50's. The strong thermal gradient between the land and the lake will still allow wind gusts to reach 20-25 mph.
As the surface high makes its way over the Great Lakes, skies tomorrow night should remain mostly clear, with lows once again in the upper 30's and low 40's. Winds will turn to the east by early Sunday morning, eventually becoming southeasterly throughout the day in response to low pressure deepening on the foothills of the Rockies in eastern Wyoming, ahead of a broad trough moving across the western CONUS.
With winds turning to the southeast, and an upper ridge axis making its way over our area on Sunday, temperatures in inland areas should make a run towards the mid to upper 60's, with a stubborn easterly lake breeze causing lakeside areas near the city to peak in the lower 60's. Meanwhile, high temperatures in lakeside areas further north in Lake county may only reach the mid to upper 50's, all under mostly sunny skies.
Sunday night will be relatively mild due to increasing southerly flow dropping temperatures only to the low to mid 50's under partly cloudy skies, all in response to the aforementioned low in eastern Wyoming pushing to the east into the upper Midwest throughout the night. Rapid surface pressure falls will result in a low level jet moving east from Iowa into northwest Illinois, and weakening throughout the night. This may result in a few showers and storms popping up (~15% PoP) to the far northwest of the Chicago metro early Monday morning, though the lower boundary layer looks to be relatively stable based on the latest soundings, so any storms that form will likely remain elevated.
Most of the rest of the day on Monday appears to remain quiet, under mostly sunny skies. Robust SSE WAA will likely push high temperatures into the upper 70's by the city, and low 80's further inland, along with dew points in the low to mid 60's by sunset.
Throughout the latter half of the afternoon, a strong line of thunderstorms will form up, tied to the low in central Minnesota, extending southward into Iowa. This will eventually make its way over our area in the mid to late evening time frame on Monday night. With vertical mixing having eliminated the cap that inhibited convection earlier in the morning, along with 1,500+ J/Kg of surface based CAPE, 40+ knots of 0-3 km shear, and a 0-6 km shear vector relatively parallel to the front, development of this line into the QLCS with strong to severe thunderstorms seems likely. Will need to continue to track this system to pin down exact timing, as well as potential for damaging winds, hail and tornadoes, though at this range all severe threats are still within the realm of possibilities.
After another round of warm 70's and 80's high temperatures, along with showers and storms early Tuesday afternoon, a cold front will hit us. This will send lows Tuesday night into Wednesday plummeting back down to the low to mid 40's, as another center of high pressure settles in throughout the upper Midwest.
Last Update: 4/21/2025 9:30 PM CDT
Lingering stratocumulus in the wake of the departing surface low into Ontario should continue clearing out throughout the evening, as a surface ridge builds in from the south. This has resulted in a weakened surface pressure gradient, which has since calmed breezy wind speeds from earlier down to the single digits, where they will remain for the rest of the night. Mostly clear skies and calm winds will allow for a strong radiational cooling regime tonight, allowing lows to drop to the low 40's near the city, and upper 30's further inland. This may also result in patchy low level fog in grassy areas and near rivers, and possibly even a light coating of frost for areas far outside the Chicago metro.
The upper air should return to mostly zonal flow by tomorrow morning, before a weak upper level disturbance passes over our area tomorrow afternoon, bringing chances for scattered showers and storms (30-60%) that will persist through the overnight hours into Wednesday. Robust mid level flow on the southern flank of the upper jet, in conjunction with sufficient instability atop a well mixed boundary layer, and a relatively low freezing level (generally between 9,000-10,000 ft) may allow for potentially damaging winds and small hail in some of the storms. However, a shallow nocturnal inversion layer will likely work to ease the surface winds into tomorrow night.
Temperatures tomorrow will be dependent on the showers and thunderstorm coverage, but most areas near the lake should hit the upper 60's, while areas further inland will top out in the low 70's. Lows tomorrow night will drop to the low-mid 50's in wake of the passing storms.
After a brief lull Wednesday morning, another weak upper level disturbance will pass to our northwest Wednesday afternoon-evening, bringing more chances of isolated to scattered showers and storms (20%). Similar risks to Tuesday's activity still apply here, with substantial deep-layer instability, strong mid level flow, and a shallow freezing level, which are all conducive to damaging winds and small hail development. However, precipitation coverage appears to be much more limited Wednesday afternoon-evening, likely due to the lack of sufficient moisture. Similar highs to Tuesday with upper 60's lakeside and low-mid 70's inland under partly sunny skies. Another mild, cloudy night Wednesday night with lows once again in the low-mid 50's
Skies will clear up early Thursday morning, and winds will turn southerly throughout most of northern Illinois, allowing highs to surge into the upper 70's and low 80's inland. Meanwhile, a lake breeze will limit lakeside highs to the mid-upper 60's. With the lake breeze, and a mid latitude cyclone moving ENE through Iowa throughout the day, potential exists for a backdoor cold front to send temperatures plummeting into the 50's by dusk.
Low level forcing for ascent increases Thursday night as the warm sector wraps into our region, along with sufficient moisture to trigger widespread showers, and some thunderstorms Thursday night (40%) through Friday (60%). Due to the vertically stacked nature of the surface low directly underneath its parent trough, and lack of sufficient deep-layer instability, the threat of damaging winds, hail, and the like are much lower with this system than the ones earlier in the week. However, it appears to be rather slow moving, which may bring about flash flooding risk in poorly drained areas.
The cyclone will exit our area after another round of potential thunderstorms (30%) overnight Friday into Saturday. Then, a broad upper riding pattern takes shape over most of the eastern half of the CONUS, and the baroclinic zone pushes to the south of us, resulting in cooler and drier conditions for this upcoming weekend.
Last Update: 4/14/2025 10:00 PM CDT
Vertical mixing tapping into 40+ knot flow atop a weakened surface inversion layer this morning brought breezy conditions throughout our area today, which has managed to rapidly dry out the boundary layer, with most locales reporting relative humidities at or below 30%. With these exceptionally low relative humidities, and winds gusts topping out between 35-45 mph, an increased risk of bushfire will remain for the first half of this evening.
There are currently 2 major upper shortwave troughs crossing the north central CONUS this evening. The weaker wave responsible for last night's cold frontal passage is currently pivoting northeastward across Lake Huron into coastal Ontario. The second, stronger wave is currently moving ESE through central Iowa, and will eventually pass over our area in the overnight hours above a second, stronger cold front. Vigorous CAA behind the front will steepen low-mid level lapse rates, which may allow some of the scattered showers and storms currently moving ESE across the Mississippi river into northwest Illinois to persist into the Chicago area tonight. However, with the currently very dry lower boundary layer, and relatively scattered distribution of showers, any precipitation that makes it over our area tonight will likely be relatively weak and isolated. Despite low POP's, the steepend lapse rates underneath robust mid level CAA will continue to allow 40+ knot flow to mix down to the surface, allowing locally sustained winds of up to 20 mph, and gusts up to 45 mph.
Gusty winds should ease throughout the afternoon tomorrow, with a weakening surface pressure gradient as the primary trough axis shifts to the east, allowing skies to gradually clear throughout the day as well. Although skies should clear out by the early evening hours, substantial northwesterly CAA will severely limit diurnal heating tomorrow afternoon, with most areas struggling to make it to the low 50's, and areas in northwest Indiana topping out in the mid 40's, with a persistent lake breeze.
Skies will remain mostly clear tomorrow night as a surface ridge pushes NNE from the southern Great Plains/Mississippi River valley, allowing impressive radiational cooling to bring lows down to, or just below freezing. As the ridge passes to our south Wednesday-Thursday, an increasing surface pressure gradient across the Great Plains will cause a southerly wind shift late Wednesday afternoon. This will allow highs to push mid-upper 50's on Wednesday (upper 40's lakeside), and mid-upper 60's on Thursday, under mostly sunny skies.
Thursday evening through the first part of this weekend looks to be rather active, with a massive upper trough from the Pacific Northwest deepening over the Rockies, along with broad southwesterly flow bringing warmer than normal temperatures and moisture into our area. This all sets up chances for showers, and potentially severe thunderstorms between Thursday evening and overnight Friday into Saturday.
Last Update: 4/02/2025 2:00 AM CDT
Aided by a strong 140+ knot upper jetstreak rounding the base of an upper trough crossing the Rockies, a powerful midlatitude cyclone and its associated 980's mb surface low in central Kansas will continue to move ENE overnight into northwest Missouri by daybreak. The attendant warm front will swing to the northeast from central Oklahoma into the Mississippi River Valley in southern Illinois throughout the night, with a powerful, 70+ knot low level jet developing in the area of rapid surface pressure falls ahead of the front.
The presence of a strong near surface stable layer, as well as lack of vertical mixing in the nocturnal boundary layer should spare our area from the full magnitude of the jet, but a strengthening low level pressure gradient will still allow gusts of 30-40 mph to prevail throughout the night. The northerly advection of warm, moist air behind the front into our much cooler, drier environment will result in strong isentropic ascent, thus increasing the coverage of showers and storms through the night, primarily north of I-80.
That strong stable layer ahead of the warm front, combined with strong enough low level shear to develop a critical layer, and the passage of the upper jetstreak through northwest Missouri and the southern half of Iowa overnight, may lead to the development of gravity waves moving east through our area. If these waves interact with convection in northwestern Illinois during the late overnight - early morning hours, it could result in locally damaging winds ahead of the encroaching storms.
Isentropic ascent, along with relatively steep lapse rates above the stable surface layer may result in impressive elevated CAPE, with MUCAPE up to 1500 J/Kg in the early-mid morning for some locales. 40+ knots of effective shear, along with decent instability may result in some weak, isolated supercells in the mid morning hours, which may bring hail as big as 1 inch in diameter (~grape size). Storm training along outflow boundaries may produce isolated 1 hr QPF totals of over 1 inch, which may pose a flash flood threat for areas with poor drainage.
Evaporative cooling from the morning storms, in addition to a chilly lake breeze should stall the northward advance of the warm front into our area until the early afternoon. Once the front passes, temperatures will surge from the mid 40's ahead of the front to the mid 60's - low 70's behind the front, along with dew points as high as the mid 60's.
Despite persistent convection in the morning being detrimental to the development of further storms later in the afternoon, the immense magnitude of the mid-latitude cyclone passing to our northwest looks to mostly recover the air mass in our environment throughout the afternoon. Strong low level shear, with over 400 (m/s)^2 of effective inflow SRH, coupled with LCL heights as low as 100 m, certainly support the development of a few tornadoes in the mid-late afternoon. However, convergence along the front appears to be relatively weak, which will make it difficult for storms to even initiate, with weaker instability present.
With strong low level shear, low LCLs, and immense amounts of moisture all competing against weak-modest instability, a wide range of possibilities are still on the table for tomorrow afternoon. If instability remains weak, we may see some isolated, non-severe convection, or even none at all. However, if sufficient instability is reached, there may be a threat of strong, fast moving tornadic supercells passing through our area mid-late tomorrow afternoon. Additionally, with a tight surface pressure gradient in place behind the warm front, wind gusts of 40+ mph are likely to persist through the afternoon and early evening.
A cold front will pass us from the northwest throughout the night Wednesday into Thursday morning, before eventually stalling out near the Ohio River Valley by daybreak. Gulf moisture will continue to feed into the frontal boundary, producing more showers. Fortunately, our area will remain far enough north of this precipitation that we should remain mostly dry until later Friday afternoon, save for a few scattered showers in the far south suburbs overnight Thursday into Friday.
Last Update: 3/24/2025 11:40 PM CDT
Breezy winds that have prevailed across our area earlier today have since ceased with the northeastward ejection of the surface low across the Great Lakes into Canada, as well as the nocturnal inversion setting in, thus shutting off vertical mixing and decoupling surface winds from the upper air.
A baroclinic zone will be set up throughout the night across northeast Iowa as cold pockets of air near the surface push ESE into north central Illinois. The resultant boundary may spring up a few scattered rain/snow showers to the far south and west of the Chicago metro. A pocket of dry air near the surface in our area should keep any precipitation from reaching the ground overnight in Cook county. Better chances of precipitation come tomorrow morning through afternoon as plumes of moisture arrive from northeast Iowa within the baroclinic zone, but again impacts will likely be limited to the far southwestern locales of the Chicago area.
Seasonable temperatures will continue through midweek with lows just above/below freezing tonight and Tuesday night under partly cloudy skies. Winds will turn NNE off the lake late tomorrow afternoon, which will moderate highs to the lower 40's for shoreside communities, while areas further inland will reach upper 40's and low 50's, all under partly sunny skies.
The second half of the week will be characterized by the upper trough currently in the eastern half of the CONUS making its way eastward and eventually ejecting into the Atlantic as the weekend approaches. Meanwhile, the massive upper ridge covering the western half of the CONUS will push eastward into our area by Thursday night, as a Pacific trough builds into the west coast early Thursday afternoon, before crossing the Rockies this weekend.
There continues to be model disagreement regarding the placement of a mid level, low amplitude, longwave disturbance moving through the area Wednesday night - Thursday. The GFS has this disturbance placed further to the north moving southeast across the UP into northern mainland Michigan, while the NAM and ECMWF have it pushing southeastward over Wisconsin overnight Wednesday into Thursday, before passing directly over our area Thursday morning. Interestingly, the latest run of the NAM indicates slight chances of scattered showers from the morning through early afternoon, while the GFS and ECMWF remain dry throughout the day. As for now, I will stick with NBM output and slight chances (20% - 30%) of rain showers will remain for Thursday afternoon.
There will be greater chances of seeing precipitation Thursday night as a warm front pushes into northern Illinois, with most models depicting scattered showers Thursday evening through Friday morning for the Chicago area. Uncertainty remains as to how far northward the warm front will push into the day on Friday before stalling out. The ECMWF and GDPS have it pushing deep into central Wisconsin, resulting in much warmer air in our area, with highs easily pushing the low to mid 70's. Meanwhile, the GFS has it stalling out near the lake, with a boundary extending northwestward into Wisconsin, leaving most of the area in the mid to upper 60's for highs, while Lake county doesn't even make it past the low to mid 40's.
The weekend looks to be fraught with more rain and potential thunderstorms, as the aforementioned Pacific trough exits the Rockies, and makes its way across the Plains into the Midwest, but details with timing and intensity of said storms remain uncertain.
Last Update: 3/18/2025 12:45 AM CDT
A large upper trough has built into the Pacific coast earlier this evening, and will continue to move across the Rockies overnight into tomorrow, creating an area of lower pressure stretching all across the Rockies northeastward into the Great Lakes. Meanwhile, an upper ridge has begun to build northward from the Gulf Coast, and will eventually cover most of the eastern half of the CONUS by early tomorrow afternoon. The tightened pressure gradient between these 2 systems will allow breezy conditions to continue in our area for most of the overnight hours, with an encroaching low level jet ahead of a pair of surface lows in the upper midwest and central plains. A mid level shortwave will continue to pass north of us overnight, pushing the upper midwest low northeastward into the Michigan UP and Lake Superior, before its associated cold front shoots southwards tomorrow morning-afternoon before finally stalling around the Illinois-Wisconsin border.
The aforementioned upper trough pushing through the Rockies, and consequential tightening pressure gradient will greatly enhance southerly winds tomorrow, as we will remain in the warm sector east of the trough. Along with stalling the cold front at the Illinois-Wisconsin border, these southerly winds will enhance surface warming and decrease relative humidities, which along with the breezy winds will continue an increased risk of bushfire tomorrow afternoon. Winds closer to the lake will turn slightly south easterly early in the afternoon, creating a lake breeze for the Northern IL and Southern WI shoreline. Thus, while highs tomorrow in most areas will reach the mid 60's and lower 70's further south near I-80, areas affected by this lake breeze will likely hold to the upper 50's.
Breezy southwesterly winds and persistent cloud cover will hold lows to the mid 50's Tuesday night as a warm front swings northeastward across north central Iowa into northwest Illinois, supporting scattered showers and possibly some elevated convection. An elevated mixed layer should keep our area dry for most of the early morning hours on Wednesday, but better forcing and increasing instability should start springing up some scattered showers and potentially a few isolated thunderstorms after noon.
A cold front will approach the area from the southwest late Wednesday afternoon into the early evening hours. Being colocated with the left exit region of the 500mb jetstreak, this front will provide much deeper forcing for strong showers and storms. This forcing, along with 500-600 J/Kg of surface CAPE, up to 70 knots of bulk 0-6 km shear, and the elimination of the surface cap by the early evening, all can support some isolated severe storms in areas with substantial instability. The increased low level lapse rates in the early evening certainly bring potential for gusty winds and hail, and with substantial deep layer shear, along with winds turning southwesterly to be more perpendicular to the cold front, the risk of rotating updrafts and an isolated tornado or two cannot be ruled out.
The dry slot slips in after about 8-9 pm Wednesday evening, giving us a brief break from precipitation before snow/wintry mix showers on the back side of the cold front hit us around 11 pm. Most of the boundary layer should be cooled off enough by then to support snow (save for the surface), but with surface temperatures so close to freezing accumulation will likely be no more than around an inch or two, with the highest amounts in the coolest areas far to the northwest of the city. Along with these snow showers, gusty 30-40 mph will persist throughout the night and into Thursday morning as the tightened pressure gradient behind the low comes overhead.
Snow showers will likely exit to the east by mid morning Thursday as skies begin to clear throughout the afternoon. Cooler WNW winds, along with evaporative cooling from the recent snowfall will hold highs to the mid 40's in most areas Thursday afternoon. We will warm back up to the 50's on Friday before another upper shortwave from the central plains pushes east into our area Friday evening, likely bringing rain showers overnight Friday into Saturday morning.
Last Update: 3/07/2025 12:40 PM CST
A mid-upper level shortwave has ejected out of the Rockies last night, spawning a surface low currently moving eastward across NE Kansas into central Illinois this afternoon. Southerly flow driving WAA, as well as isentropic upglide is providing plenty of forcing for precipitation throughout our area this afternoon. Precipitation currently moving in from the west will exit to the east of us early this evening. Precipitation currently falling as snow will likely predominantly switch to rain later this afternoon as WAA continues to set in. However, with a surface temperature currently sitting at around 37 at KMDW, the ground will melt any snow as soon as it touches the ground throughout most of the area, save for a few areas to the far NW of the city. While northern areas will be able to accumulate possibly up to a half inch due to colder air, steep lapse rates and mid-level frontogenesis NE of an axis running from Lacon to Pontiac will result in some heavier bands of precipitation south of the city. Again, with surface temperatures substantially above freezing, even in the heaviest bands of precipitation, accumulation will likely amount to no more than a bit of sludge on untreated roadways.
As the system exits to the east this evening, skies will clear as NW flow driving CAA drops lows into the upper 20's for most of the area.
Drier, and warmer conditions will prevail across the area for most of the coming week. A system passing far to the north of our area on Saturday will result in some slight WAA as winds turn out of the SW, bringing sunnier skies pushing highs into the mid 40's. This warming trend continues on Sunday and Monday as a ridge downstream of a longwave trough over the Rockies will allow highs to soar into the mid 50's on Sunday, and even push lower 60's on Monday. SW wind will also inhibit any lake breeze, allowing higher temperatures to push closer to the shoreline.
Last Update: 2/24/2025 10:10 PM CST
This afternoon, the combination of warm SW winds, rapidly melting snowpack owing to high dew points, and decreasing cloud cover later in the afternoon pushed highs up into the mid to upper 50's throughout most of the Chicago area.
A strong mid level shortwave currently moving east across NW Iowa and southern Minnesota will continue to keep skies cloudy across the Chicago area tonight. Relatively weak moisture, in combination with strong ascent, and instability will continue to bring scattered showers throughout the evening, before mostly subsiding by midnight. As a result, this will keep overnight lows in the mid to upper 30's. Weak winds may lead to some patchy fog in some areas where precipitation fell, but given the low rainfall intensities this is unlikely to be a widespread hazard.
Tomorrow, a shortwave ridge will move over our area to keep temperatures well above normal for this time of year. However, weak cold air advection evident from near freezing 850 mb temperatures will inhibit highs from reaching temperatures recorded this afternoon, with most areas unable to make it out of the upper 40's and low 50's. A relatively weak pressure gradient and large temperature difference between the lake and the land will bring a lake breeze later in the afternoon, dampening highs for areas near the shore.
A small wave from a deep Pacific trough will pass just to the north of our area Tuesday night into Wednesday. Low level frontogenesis colocated with the right entrance region of a 90+ knot upper jet will create some rain showers in the Chicago area overnight Tuesday into Wednesday morning. Moderate instability may lead to a few lightning strikes, though widespread thunderstorms are not expected. Lows will once again remain in the mid 30's due to the expanding cloud cover.
Despite the showers expected on Wednesday morning, Southerly and westerly winds will advect warm air into our area throughout the day, leading to highs in the low to mid 50's.
While skies will continue to be relatively cloudy Wednesday night, a cold front passage in the early evening hours will drop temperatures back down to the mid 30's for overnight lows.
Late Wednesday night, a weak shortwave surges southeastward out of the southern Canadian plains, potentially bringing a few light showers to our area in the early afternoon hours on Thursday. Winds will turn northwesterly, so highs will only make it to the mid 40's Thursday afternoon.
Ensembles are still in agreement that a large shortwave will dart southeastward out of the Canadian plains Thursday night, before making its way over the Great Lakes by Friday afternoon into Saturday. The tight pressure gradients associated with this wave will bring breezy winds Friday-Saturday, with some locations experiencing gusts of 40+ mph on Saturday afternoon, based on the latest NBP output.
Saturday night into Sunday, a surface ridge will set up in northern Minnesota along the Canadian border, bringing a cooler, drier northerly wind to the Chicago area on the second half of the weekend.
Last Update: 2/18/2025 2:00 AM CST
Excessive cold is the primary weather concern for the rest of this work week. With the arctic high pressure center currently set up over the northern plains and southern Saskatchewan, and gradually moving southeast over the next few days, bitterly cold temperatures with highs in the low to mid teens and lows in the single digits below to single digits above zero are likely to persist through Thursday.
Cloud cover will continue to shift southwards through the night, meaning much colder lows than initially forecasted, down to 5-6 below zero are likely to occur in the far northwest suburbs, while areas south of I-80 might not even make it down to 0. With the recent northwesterly wind shift providing a long fetch over Lake Michigan, and the large temperature difference between the air and the lake, favorable conditions for lake effect snow will persist across portions of northwest Indiana through Tuesday night. Snowfall rates will likely be very low, however, with the extremely cold air mass present boosting snowflake crystallization, an inch or two of accumulation cannot be ruled out. Breezy northwesterly winds creating wind chills down to 15 to 20 below zero will also persist through the day on Tuesday.
With the Canadian high still inducing the strong NW wind on the Chicago area, similar conditions will prevail on Tuesday as they did Monday, with possibly a degree or two warmer on the high (13-14) owing to clearer skies.
Increasing clouds will moderate temperatures on Tuesday night, albeit slightly, with lows in the mid single digits, and the NW wind holding wind chills down to 8 to 12 below zero. Areas to the far northwest of the city and outside of the cloud field will likely continue to see frigid lows more characteristic of the beginning of the week, with certain places falling close to or even below 0, and wind chills of 15 to 20 below.
An upper level shortwave disturbance originating from the northern plains will approach our area on Wednesday, leading to a continued increase in cloud cover. Highs will be slightly warmer than Tuesday's despite the encroaching clouds, with most locations in the Chicago area reaching the mid teens, and wind chills dampening to 5 to 10 below 0.
Wednesday night, the aforementioned shortwave disturbance may create a few light snow showers, particularly for regions in NW Indiana downstream of the WNW lake breeze. The colder air present may help to create a light dusting on elevated surfaces, but no substantial accumulation is expected. Lows will be once again moderated by the cloud cover, with mid single digits across most of the Chicago area, and wind chills of 5 to 10 below.
Thursday, skies will clear out from Wednesday night's event, with highs potentially reaching the lower 20's.
With the arctic high moving southeast into the Ohio river valley by Friday, winds will shift southwesterly and highs will likely see the mid 20's and even upper 30's by the latter half of the weekend.
Last Update: 2/13/2025 7 PM CST
Cooler temperatures prevailed today across the Chicago area, despite clear skies. Steepend pressure gradients created a strong WNW wind that has pushed cold, dry air from the upper midwest into our area, offsetting the enhanced surface heating from the clear skies. This has managed to keep highs down to the upper teens, with wind chills bottoming out in the single digits.
The surface high currently in central Missouri will continue to push eastward into the Ohio river valley into the evening, thus weakening the pressure gradient, as well as the surface winds. Synoptic descent in the mid to upper levels will stabilize the atmosphere, keeping the skies mostly clear throughout the night, save for a few high clouds popping up into the morning hours. The weakened surface winds, clear skies, and few inches of snowpack still on the ground will create a strong radiational cooling regime, causing lows close to 0, and wind chills as low as -10.
Clouds will increase throughout the day tomorrow as the next winter storm system approaches from the southwest. This system is characterized by substantial low to mid level warm air advection, which when combined with the dry air mass already in place, will limit the southerly extent of heavy snowfall. On one hand, the drier air mass in place in the low to mid levels favors higher snow to liquid ratios, which would create high snow totals with less dense snow. While on the other hand, the warm air advection and consequential higher temperatures associated with it favor lower snow to liquid ratios, creating lower snow totals with denser snow. Thus, cooler areas closer to the WI-IL border will receive the highest amounts of snow, while areas further south in Cook county will receive lower snow totals. Most of the models (besides the GFS) have slowed down with the progression of the system these past few days, creating a much lower probability of precipitation during the day tomorrow, with a slight chance of non-accumulating flurries before 6 pm. Despite the increase in cloud cover, the warm air advection associated with this system will allow daytime highs to reach the upper 20's.
Snowfall rates will ramp up quickly after about 6 pm as the bulk of the system makes its way over our area. As low level warm advection begins to lift throughout the night, the risk of freezing rain increases, particularly for areas south of I-80. Most of the system should move off to the east of our area by around 2 am, but intermittent flurries are still possible throughout the night. Due to the aforementioned North-South stratification of snowfall totals, I will use a 13:1 snow to liquid ratio for areas in northern Cook and Lake counties, and a 10:1 ratio for areas in southern Cook county. With a projected QPF of around 0.1-0.3 inches, this means that 1.3-3.9 inches of snow will fall further north, with just 1-3 inches falling to the south. With breezy winds, and light, powdery snow further north, there will likely be a risk of blowing snow in said areas. With heavy cloud cover present throughout the night, lows will only make it down to the mid 20's.
Brief, intermittent flurries are possible until around 9 am as Friday's system makes its way off to the east. The next system rolls in by 11-noon, being induced by a mid level shortwave moving across Iowa into northern Illinois. Warmer temperatures associated with this system mean that precipitation could be in the form of a rain/snow mix, particularly for areas in southern Cook county and NW Indiana. This rain/snow mix will continue to fall throughout the afternoon, accumulating between a half inch to an inch of snowfall, with highest amounts further north in Cook and Lake counties. Warm advection associated with this system will bring high temperatures up to the mid 30's.
The rain/snow mix will likely switch over to snow early Saturday evening as the temperatures drop below freezing. Then, low level lapse rates will steepen as a polar cold front hits our area late Saturday night, bringing more snow showers along with it, and will impact our area into the first half of the day on Sunday. With heavy saturation still present Saturday night, lows will still only be in the lower 20's, despite the cold front passing. However, late Sunday into next week we will see an arctic air mass move over the area, bringing bitterly cold sub-zero temperatures along with it.