textproduct: Chicago

KEY MESSAGES

- A brief break in the pattern is expected later today through the day on Friday before another storm system and potential severe weather arrives Friday late afternoon and evening.

- Cooler air arrives into early next week and may bring frost/freeze concerns early Sunday and Monday mornings.

DISCUSSION

Issued at 257 PM CDT Wed Apr 15 2026

Through Thursday...

The primary weather focus in the near continues to revolve around the expectation for additional rounds of showers and thunderstorms, particularly this evening.

A recent surface analysis indicates that an area of low pressure resides across southeastern NE, with an associated surface cold front extending south-southwestward into the TX Panhandle. While our area has remained cloudy, increased insolation west of the area in the vicinity of the surface low and frontal boundary continues to destabilize the very moist (dew points in the low to mid 60s) low-level prefrontal airmass across MO into south central IA. This will set the stage for additional thunderstorm development mid to late this afternoon west of our area as increased forcing for ascent associated with the mid-level impulse ejecting into the Mid-Missouri Valley overspreads the frontal boundary. After storms onset, a gradual upward growth into an MCS is anticipated this evening as they shift eastward across the Mississippi river. It appears the primary severe weather threat with these storms will be west of our area, with storms likely to be on a weakening trend as they progress eastward across northern IL during the mid to late evening hours. Nevertheless, a continued favorable kinematic environment overhead may continue to support a threat for localized strong wind gusts with the weakening line of storms.

Heavy rainfall is expected to accompany these storms through the evening, and this does continue to add concerns for possible hydro concerns tonight. However, it appears the heaviest rain rates may remain more progressive with the moving line of storms tonight. Accordingly, it appears the threat for significant flash flooding is lower than previously thought. Nevertheless, areas across far northern IL that received heavy rainfall last night will be most at risk for additional flooding concerns., With this in mind, we have opted to hold onto the going flash flood watch for this evening.

Shower and thunderstorm coverage is expected to become more widely scattered overnight tonight into Thursday as the main mid-level impulse shifts overhead. As an afternoon lake breeze develops and pushes inland across northeastern IL and northwestern IN Thursday afternoon in the wake of the surface low, this may act as a focus for additional isolated shower activity for a few hours Thursday afternoon. Outside of this, conditions will be drying out Thursday afternoon and evening.

KJB

Friday - Saturday:

Strong southerly warm and moist convection will return into the day on Friday ahead of an approaching cold front. This boundary is expected to progress across the area sometime late Friday into early Saturday morning paired with a line of thunderstorms, some of which could be severe. Suspect that less favorable diurnal timing of any lingering storms into the morning on Saturday may limit the overall severe threat here locally before storms reintensify east of the area into the rest of the day. Stay tuned!

Saturday night onward:

In the wake of the early Saturday cold front, a much colder airmass (relative to what we have had over the past several days) will settle into the region over the weekend. Overnight low temperatures may drop into the 30s, with some near to sub- freezing temperatures possible across interior northern Illinois. Lighter winds in place Sunday night may allow for frost development outside of Chicago and will be something for those with agricultural interests to monitor over the next few days.

The cooler conditions will be rather short-lived with extended guidance favoring a return toward high amplitude ridging across the central CONUS and unseasonably warm temperatures returning to the region by midweek next week.

Petr

AVIATION /06Z TAFS THROUGH 12Z FRIDAY/

Issued at 1233 AM CDT Thu Apr 16 2026

Forecast concerns include...

- Wind directions during the early overnight hours. - Wind shift to northeast Thursday afternoon. - Mvfr cigs overnight into Thursday. - Periodic shower chances.

A line of showers with embedded thunderstorms will continue moving away from the terminals through the early overnight. There will be continued chances for showers through Thursday afternoon with quite a bit of uncertainty for timing and have included prolonged periods of vicinity shower mention. It appears the best chance for additional showers will be from late morning through early afternoon but timing will need to be adjusted as trends emerge. An isolated thunderstorm is possible, but no mention with expected low coverage.

Prevailing winds are shifting to the east southeast across northwest IL in the wake of the showers and this southeast shift is expected across the Chicago terminals, at least for a short time, before winds turn back to the southwest early this morning. Confidence is low for specific directions and changes may be needed. Winds may begin to gust into the 20kt range by daybreak as directions slowly turn more westerly Thursday morning. Confidence is also low for winds Thursday afternoon. Directions will likely continue turning to the northwest Thursday afternoon and then a lake breeze boundary is expected to move inland during the mid/late afternoon. Timing confidence has decreased and will need to be refined with later forecasts. Winds will turn southeasterly Thursday evening.

Prevailing mvfr cigs are expected to develop overnight, continue Thursday morning then lift to vfr Thursday afternoon. However, low cigs are possible with the lake breeze boundary. In addition, there will likely be fog over Lake Michigan and some of the model guidance is spreading this fog inland Thursday evening and across the Chicago terminals early Friday morning. Confidence is too low to include any lower cigs or fog for ORD/MDW in their new 30 hour tafs and trends will need to be monitored. cms

LOT WATCHES/WARNINGS/ADVISORIES

IL...Flood Watch until 1 AM CDT Thursday for ILZ003-ILZ004-ILZ005- ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ019-ILZ020- ILZ021-ILZ023-ILZ032-ILZ103-ILZ104-ILZ105-ILZ106-ILZ107- ILZ108.

IN...Flood Watch until 1 AM CDT Thursday for INZ001-INZ002-INZ010- INZ011.

LM...None.