textproduct: Chicago

KEY MESSAGES

- Severe thunderstorms Tuesday afternoon and evening, with the potential for very large hail, damaging winds and tornadoes.

- Potential for heavy rain and localized flash flooding Tuesday afternoon into Wednesday morning.

- Possible very strong winds (40+ mph) Thursday night/Friday.

DISCUSSION

Issued at 220 AM CDT Mon Mar 9 2026

The primary forecast concern is the severe weather potential Tuesday afternoon into Tuesday evening.

For today, high temps are expected to warm well into the lower 70s which if these materialize will be new records for today for much of the area. Southwest winds will remain breezy, gusting into the 25 to 30 mph range at times. The models continue to show a weak disturbance lifting northeast across the Ohio Valley this evening with a chance for a few showers/sprinkles across the far southeast cwa. There has been fair agreement with this for several model runs and added slight chance pops for this evening for the far southeast cwa.

A cold front will be moving south across the western Great Lakes this evening and the models are now showing this front entering northern IL after midnight tonight, possibly as far south as the I-88 corridor by daybreak Tuesday morning. Most of the cams along with the NAM/GFS have this front continuing south to the I-80 corridor by Tuesday afternoon. There will be a large temp gradient along this boundary with temps falling through the 50s and possibly into the 40s behind the front, while temps south of the boundary will be in the 70s. Have trended colder with temps for Tuesday with this further south progression of the front. However, temps will likely needed to be lowered further if these trends with the cold front continue.

As low level moisture slowly increases later today into tonight, the models are showing fog developing over Lake Michigan and have added patchy fog overnight into Tuesday. This fog will likely become dense over the water and some of this fog may move inland or develop along/ahead of the front as it moves south on Tuesday, with fog mention possibly being needed over land with later forecasts.

Low pressure will develop over the Plains Tuesday and move northeast across the local area Tuesday night. As it does, scattered thunderstorms will develop during the mid/late afternoon and continue through Tuesday evening, slowly moving east southeast Tuesday night. The SPC Day 2 outlook has expanded the enhanced (level 3) severe risk northeast through roughly the I-88 corridor. All modes of severe weather will be possible along and south of the boundary. North of the boundary, very large hail will still be possible with elevated thunderstorms. The end time of the severe thunderstorm threat is somewhat uncertain but may continue through late evening for much of the area and into the early overnight hours (early Wednesday morning) for the far southeast cwa. With this enhanced severe risk, have included severe mention in the grids/zfp for late Tuesday afternoon and then all of Tuesday evening.

Heavy rain is also expected with these thunderstorms and there is the potential for training thunderstorms, especially across the southern half or so of the area Tuesday night into Wednesday morning. Wherever this materializes, there will be the potential for localized flash flooding. Rain will likely be ongoing Wednesday morning and may continue through early afternoon as it ends from northwest to southeast across the area. Colder air will be spreading across the region and there may be a mix with or change to light snow, but not expecting any accumulation at this time.

Another strong storm system is expected to move across the northern Plains and upper Midwest Thursday night and across the northern Great Lakes region Friday. Strong southerly winds will develop across the area Thursday evening ahead of a trailing cold front from this storm system which will move across the area Friday morning. Winds will shift west/northwest behind the front and continue to be strong on Friday. Still several days away but given the track and strength of this system, wind gusts 40+ mph are possible. The local area appears to be on the south edge of the precipitation, which could end as a rain/snow mix Friday morning.

No significant changes to the model trends for this weekend into early next week. It still appears active with a system moving across the area this weekend with the potential for a rain/snow mix then a pattern shift to colder early next week with perhaps additional snow chances. cms

AVIATION /12Z TAFS THROUGH 18Z TUESDAY/

Issued at 607 AM CDT Mon Mar 9 2026

Marginal LLWS will linger at the outlying TAF sites early this morning. Otherwise, south-southwesterly breezes will continue today with periodic gusts around 25 kts. Gusts will ease this evening.

Low-level moisture will surge northward across the region tonight into early Tuesday morning. With this moisture will come the potential for MVFR/IFR cigs and vsbys. At this time, it remains a bit unclear just how far west any low cigs will develop. Have introduced a TEMPO group for near-IFR cigs at GYY but have withheld a lower mention at the other TAF sites through 12z Tuesday due to low confidence. At DPA, ORD, and MDW, have added a mention of some BR, with some potential that lower conditions may be needed in future issuances.

Eventually, a shallow cold front will push off the lake Tuesday morning resulting in a N/NNE wind shift. Some variability in the specific timing remains, but have added a wind shift at ORD at 12z and an hour later at MDW. IFR cigs should develop in the wake of the front, along with the potential for IFR vsbys.

Carlaw

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory until 10 AM CDT this morning for the IL and IN nearshore waters.