textproduct: Chicago

KEY MESSAGES

- Strong winds will gradually ease today.

- Wind driven light snow will end this morning, though flurries may linger into the afternoon.

- Some light snow or flurries are possible Tuesday, with a slightly better chance of light snow Wed afternoon and evening.

DISCUSSION

Issued at 333 AM CST Mon Dec 29 2025

Powerful cyclone responsible for the active weather over the last 24 hours has moved to Lake Huron and deepened to around 980 mb as of 09z. Water vapor imagery early this morning shows a well defined vort max over Wisconsin, embedded within the broader large mid-upper level cyclone. Ascent associated with this WI vort has been resulting in fairly widespread light snow across WI into northern IL early this morning. Light snow of varying intensity is likely to continue early this morning, ending from the northwest after sunrise. Guidance has this light snow ending between 12-15z this morning as the shortwave over WI shifts southeastward, with the associated synoptic ascent moving east of the area. Rough extrapolation of the back edge of the snow matches the timing in guidance pretty closely, adding some confidence to the snow ending this morning. Earlier QPF guidance appears to have been running a bit high, it appears as though accumulations should generally end up in the inch or less range, highest north of I-88/I-290. Despite the expected meager snowfall amounts, road impacts are likely this morning, so plan to continue the advisory through early this morning.

Surface low is progged to continue deepening to below 980mb this morning, but as it moves farther northeast into Quebec, the pressure gradient is expected to ease today. The frequency of 45+ mph gusts is likely to begin waning by mid morning with gusts expected to be generally below advisory criteria by 18z, if not earlier, so will be pushing the ending time of the wind advisory up to 18z.

Expansive stratus deck blankets the upper Mississippi Valley and Midwest and should stick around today and likely into much of tonight as well. Temperatures within the stratus deck should generally be at or below -12C, so ice nuclei will be present and could allow for a few flurries at times today and perhaps into tonight. Have maintained the chance of flurries in the wake of the light snow today. Day shift to reassess and determine if flurries chances are needed for tonight as well.

Winds are progged to veer more northwesterly this morning in the wake of the aforementioned shortwave trough, which could allow for lake effect snow showers to back into northeast Porter County. At this point, it looks like 1-3" of snow would be the most likely worst case scenario for far northeast Porter County.

Guidance does bring a quick moving northwest flow shortwave zipping through the region Tuesday afternoon. It does look like this could result in some light snow or flurries. Didn't adjust NBM pops at this time, but plausible that snow chances may need to be increased for a potential coating of snow Tuesday for mainly northeast portions of our CWA.

A somewhat more formidable shortwave will move across the region Wednesday afternoon and evening. ECMWF has been the most consistent in bringing some light snow to the region in association with this disturbance, but the GEFS guidance has been trending higher in measurable precip chances. A thermally indirect circulation in the left region of a 140 kt jet diving into the Midwest could lead to some enhanced low-mid level frontogenesis helping support some slightly better snow chances. NBM PoPs seemed too low given the increasing model agreement and EPS and GEFS measurable precip chances, so did adjust NBM PoPs up 10-15%. If models remain consistent, then additional increases in PoPs can be expected in the coming days. It generally isn't looking like a big snow event, but it doesn't take a lot of snow to cause travel issues and these f-gen enhanced snow bands can be sneaky and overproduce at times, so something to keep an eye on for New Year's Eve day and evening. Brief shot of cold air is expected in the wake of that system, followed by a bit of moderating trend for temperatures over the weekend and into next week.

- Izzi

AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 1159 AM CST Mon Dec 29 2025

MVFR stratus with periods of MVFR/VFR SHSN over the area has exhibited decent erosion over the past few hours, but any gaps should fill in in response to daytime mixing this afternoon. Another area of stratus with some developing holes upstream over Wisconsin indicates the stratus is rather thin and prone to eroding as drier advects in from the northwest tonight. As a subsidence inversion gradually lowers to or below 2kft tonight, any remaining flurries should end early this evening and stratus should begin to SCT or clear out sometime later this evening and especially overnight from northwest to southeast.

Mid-level cloud cover will spread over the area by sunrise Tuesday, then gradually descend to low-end VFR levels by late afternoon. An associated shield of SN to the northeast is likely to brush far northeast Illinois prior to 00Z Wednesday, and may affect the Chicago terminals as early as 22Z Tuesday. Have included PROB30 -SN during this period, with the potential forecast updates to require a TEMPO with IFR visibility late afternoon into early evening.

NW/WNW winds will continue to gust to 30 knots through the daytime hours before gradually diminishing and backing W through the night. Expect WSW winds around 10 knots Tuesday morning to gust up to 20 knots in the afternoon.

Kluber

MARINE

Issued at 505 AM CST Mon Dec 29 2025

No changes made to marine headlines this morning. Michgian City is getting sustained winds near storm force with peak measured gusts so far to 57kt the Harrison-Dever Crib has storm force gusts to to 51kt. Storm force winds/gusts will likely continue for early this morning, especially over the open lake and Indiana nearshore waters. Winds should begin to gradually ease later this morning and this afternoon.

- Izzi

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...Wind Advisory until 3 PM CST this afternoon for INZ002.

LM...Gale Warning until 6 PM CST this evening for the IL nearshore waters.

Storm Warning until 3 PM CST this afternoon for the IN nearshore waters.