Ahead of an approaching cold front, Monday afternoon temperatures warmed well into the 80s – Midway peaking at 85 degrees while Chicago’s official reading at O’Hare topped out at 82-degrees. Dew-points in the upper 60s and lower 70s pushed humidity values up to uncomfortable levels, and as the front moved slowly through from the west, scattered showers and thunderstorms developed across the area – with some locations receiving over a half-inch of rain.
The leading edge of much cooler, less humid (dew-points in the 50s) Canadian-source high pressure arrived overnight. Tuesday and Wednesday the coolest portion of the high will be overhead here and mid to late-September readings will prevail. Northeast winds will assure temperatures along the lakefront and at the beaches will struggle to warm out of the 60s, while inland readings will probably peak in the low to middle 70s.
By Thursday the center of high pressure will have slowly eased off to the east, allowing southerly, albeit weak, flow to return. Temperatures will slowly modify – highs reaching into the lower 80s this weekend. Mid to upper 80s will be possible along with higher humidity and an increasing chance of rain early next workweek.