Last Update: 8/25/2025 5:20 PM CDT
Another seasonably cool day under mostly sunny skies, as the Chicagoland area experiences its first taste of fall-like weather. Most locales have topped out in the low 70's, along with a cool northwesterly breeze at 10-15 mph, gusting up to 20 mph.
This cooler than normal weather pattern can be attributed to a blocking mechanism currently taking place across the CONUS as upper level ridging expands northward into Canada from an upper high in New Mexico, while a broad trough draped across the northern half of the CONUS, and most of Canada east of the Rockies slowly makes its way eastward into the Atlantic. This has resulted in generally northwesterly flow aloft upstream of our area, which has worked in tandem with the encroaching surface high in the upper midwest to usher in cool, dry air from up north.
This pattern looks to persist over the next several days through Wednesday night, with highs ranging from the low-mid 70's (warmth slowly building throughout the week), and overnight lows ranging from the upper 40's to the upper 50's, all under mostly sunny/partly cloudy skies. A few weak shortwave ripples in the northwesterly flow may result in some isolated-scattered lake effect showers in northwest Indiana both tonight and early tomorrow night, due to the cooler airmass overhead and the warmer lake waters.
Next chance at appreciable precipitation looks to be late Wednesday night into Thursday, as a positively tilted mid-upper level shortwave digs southward out of Canada, sending a cold front across northeastern Illinois Thursday morning. Despite only modest moisture convergence ahead of the front, much cooler temperatures aloft will allow for more efficient drop condensation, likely resulting in some scattered convection overnight Wednesday night into Thursday afternoon.
Heading into this weekend, the aforementioned synoptic blocking mechanism looks to take its time breaking down into next week as a cyclone slams into the Pacific Northwest, which should result in a continuation of the cool, mostly dry pattern we've been seeing lately through the weekend, with highs in the low-mid 70's, and lows in the 50's throughout the metro.