textproduct: Chicago

KEY MESSAGES

- Areas of freezing fog early this morning.

- Possible (40-60%) period of light snow Wednesday afternoon with any snow accumulations less than one inch.

- Well below normal temperatures through the weekend with wind chills -10 to -20 expected Thursday and Friday mornings.

DISCUSSION

Issued at 216 AM CST Tue Dec 2 2025

Clouds scattered quickly as the snow ended and areas of freezing fog quickly developed, most concentrated along the I-80 corridor/ Fox Valley in IL, currently. Visibility has improved quite a bit here at LOT recently as stratus clouds moved back through. Forecast soundings also suggest low level winds will increase into the 10-12kt range over the next few hours and this may help mix the low levels enough to limit any widespread dense fog. Issued an SPS earlier for the entire area which expires at 10z, with fog mention in the grids/forecast until 12z. Will take another look for refinement before sending products this morning. Another SPS may be needed for at least patchy freezing fog through mid morning.

Any remaining light snow will end over the next few hours and plan to let the rest of the winter weather advisory expire at 09z. However, untreated surfaces may still be partially snow cover and slippery this morning.

A ridge of high pressure will quickly move across the area today with winds turning southerly by this evening and then gradually increasing in speed overnight with some gusts into the 20-25 mph range possible by daybreak Wednesday morning. Low temps will likely occur this evening, generally in the upper teens and then temps will level off an begin to slowly rise overnight.

A strong cold front will move across the area Wednesday afternoon into early Wednesday evening. Precip chances along and ahead of this front remain uncertain with guidance about equally split between just some flurries or a brief period of light snow. Blended guidance pops have jumped to likely for much of the central cwa Wednesday afternoon. If snow occurs, it will likely be a high pop, low qpf event and opted to make no changes. Snow amounts will be light, less than one inch and many areas may see just a dusting/trace.

The cold air surges into the area Wednesday night on gusty northwest winds into the mid 20 mph range, which will diminish to 10 to 15 mph by daybreak Thursday morning. Low temps will likely be in the subzero single digits across northwest IL and in the low single digits for the rest of the area, perhaps a little warmer downwind of Lake Michigan in northwest IN. This temp/wind combination will likely produce wind chills in the -10 to -15 range for most areas.

High pressure will quickly move across the area Thursday and is a bit faster in the latest guidance. This allows for some weak warm air advection by late afternoon and then pretty decent warming aloft Thursday night into Friday morning. Blended high temps in the lower/mid teens may be a touch too cold, but made no changes. However, did warm low temps Thursday night, as they will tank Thursday evening and then level off and may slowly warm by daybreak Friday. This still yields subzero single digit low temps. Even if temps level off and slowly warm overnight, southerly winds will slowly increase Thursday night into Friday morning, keeping wind chills in the -10 to -20 range for much of the area.

There remains quite a bit of uncertainty for a possible system this weekend and then perhaps another system for early next week, both of which could produce at least some accumulating snow for parts of the area. Blended guidance low chance pops seem fine for now. cms

AVIATION /12Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 541 AM CST Tue Dec 2 2025

Key Messages:

- Period of LIFR conditions likely early this morning in low stratus/fog.

- Confidence remains low on IFR/MVFR ceiling trends today and tonight. Also lower confidence in improvement to VFR late this evening/overnight as winds turn southwest and become breezy.

- Potential for light snow by Wednesday afternoon. Some spread in onset time, but have included a PROB30 at the end of the ORD/MDW TAFs for this.

Mid-level disturbance is moving east of the area early this morning, with light snow having ended across the terminals. Partial clearing overnight has lead to development of IFR/LIFR and VLIFR stratus and fog upstream across IA/western IL, which is now spreading eastward across the terminals at TAF issuance time. Expectation is that there will be a several hour period of IFR through midday, with a few hour period of LIFR/patchy VLIFR as the stratus/fog arrives. Several obs of 200-400 foot cigs across northern IL support this currently. Sub-1SM vis has been more localized, though there are a few <1/4SM to 3/4SM obs and can't rule out brief lower vsbys over the next 1-2 hours.

Model guidance continues to struggle with trends of the shallow stratus deck later this morning into this evening. Have maintained a slightly pessimistic stance with IFR cigs lingering through midday/early afternoon before improvement to MVFR. Satellite extrapolation of trailing edge of MVFR deck across central IA would suggest this not clearing out until later tonight, which is supported by some guidance. Improvement to VFR appears possible after midnight as southwest flow strengthens, though lingering low-level moisture could support continued or redevelopment of low stratus.

Speaking of winds, light westerly flow is anticipated to eventually turn more southwest late this afternoon/evening. Speeds then increase late evening/overnight as the gradient tightens up ahead of a cold front which will move across the area Wednesday. Gusts in the 20-25 kt range are possible from after midnight into Wednesday morning.

Light snow is expected to develop ahead of the approaching front by midday Wednesday. Higher chances appear to be beyond 18Z, but have included a PROB30 at the end of the ORD/MDW 30-hour forecasts.

Ratzer

CLIMATE

Issued at 225 PM CST Mon Dec 1 2025

Chicago Cold High Low Thursday 12/4 13 (1991) 0 (1893) Friday 12/5 4 (2005)

Rockford Cold High Low Thursday 12/4 7 (1991) -4 (1991) Friday 12/5 -5 (2005)

- Izzi

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory from midnight tonight to 9 AM CST Thursday for the IL nearshore waters.

Small Craft Advisory from midnight tonight to 3 PM CST Thursday for the IN nearshore waters.