textproduct: Chicago

KEY MESSAGES

- Frost/freeze conditions are expected outside of Chicago late tonight into Monday morning.

DISCUSSION

Issued at 255 PM CDT Sun Apr 19 2026

Convective showers tied to both a sharp mid-level trough and surface cold front have produced rain, snow, graupel and some lightning across across northern Illinois over the past couple hours. The intensity of these showers should continue through late afternoon as they track southeast before waning with the loss of daytime heating.

A broad surface high will then edge southeastward over the area overnight into Monday morning. Beside a low chance for some shallow lake effect clouds drifting over far northeast Illinois overnight, mostly clear to clear skies are expected. Very dry air highlighted by current dew points in the mid teens over central Wisconsin and PWATs under 0.25 inch combined with light/calm winds will allow for efficient radiational cooling tonight. The current Freeze Warning for all but central Cook County remains on track. Have opted to also include a Frost Advisory for central Cook County for mainly the near west suburbs. It is possible that the dry air limits frost development even with temps in the 32-35F range, but it seems prudent to include a headline as we are now well into the growing season.

The high pressure will bring mostly sunny skies, light winds and high temps in the 50s (40s near the lake) for Monday. Increasing southwest flow behind the departing ridge will yield much warmer conditions with highs in the 70s on Tuesday. However, a backdoor cold front below a small mid-level wave crossing the area late Tuesday afternoon into the evening may provide sufficient ascent to generate an axis of showers and perhaps a few storms. Somewhat limited low-level moisture and existing capping under the edge of an EML should limit thunderstorm coverage.

Ridging will build back into the area by Thursday, with another round of showers and storms, some potentially strong, Thursday night and Friday.

Kluber

AVIATION /00Z TAFS THROUGH 06Z TUESDAY/

Issued at 633 PM CDT Sun Apr 19 2026

Forecast concerns include...

Wind shift to northeast this evening. Wind directions Monday. Chance of showers early this evening.

A lake breeze boundary is currently moving west through ORD/MDW, shifting winds to the northeast. Speeds 10-12kt will be possible for the next hour or so. Northwesterly winds will continue west of this boundary through sunset and then speeds will diminish through the evening, becoming light and variable or calm overnight. Wind directions are challenging on Monday and may eventually favor south/southwest from late morning through mid afternoon and then slowly turn back south/southeast by early evening. A lake breeze is expected but its uncertain how far inland it will move. If it were to make it to ORD/MDW, a more easterly direction would be expected by early Monday evening.

There remains a low chance for a few showers early this evening, mainly over Lake Michigan and into northwest IN. Expected coverage is too low for any mention with this forecast. cms

LOT WATCHES/WARNINGS/ADVISORIES

IL...Freeze Warning from midnight tonight to 9 AM CDT Monday for ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012- ILZ013-ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039- ILZ103-ILZ105-ILZ106-ILZ107-ILZ108.

Frost Advisory from 2 AM to 9 AM CDT Monday for ILZ104.

IN...Freeze Warning from midnight CDT /1 AM EDT/ tonight to 9 AM CDT /10 AM EDT/ Monday for INZ001-INZ002-INZ010-INZ011- INZ019.

LM...Small Craft Advisory until 7 PM CDT this evening for the IL and IN nearshore waters.