Area Forecast Discussion

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 /18Z TAFS THROUGH 00Z TUESDAY/

Issued at 112 PM CDT Sun Apr 19 2026

Key Messages:

- Scattered showers this afternoon along with gusty west to northwest winds.

- Low confidence in the wind direction forecast for ORD and MDW tomorrow.

Scattered rain showers are ongoing in the area at the beginning of the TAF period, though the greater coverage of shower activity should diminish by 21Z. Isolated instances of graupel and a rogue lightning strike or two may also occur with this activity.

Winds will remain gusty and out of the west to northwest through this afternoon with occasional gusts as high as 30 kts or so possible. A northeasterly wind shift may occur this evening as a surface trough pushes inland off of Lake Michigan, but surface winds at this time may already be quite light. There also remains a lower-end chance for MVFR ceilings to be observed tonight after this wind shift occurs, but have maintained VFR conditions in the TAFs for now.

Tomorrow, a lake breeze is expected to develop and is more likely than not to stall in close proximity to ORD and MDW. Thus, confidence in precise wind direction trends at both of these TAF sites remains low at this time, but wind speeds do look like they'll remain at or below 10 kts for the most part tomorrow.

Ogorek

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.