textproduct: Chicago

KEY MESSAGES

- A period of light snow with accumulations up to around one half inch through may result in locally slippery travel through mid-evening.

- Accumulating snow is expected Sunday afternoon into the evening, with slippery travel conditions expected. Strong west to northwest winds with gusts to 40 mph with an cold front will follow shortly behind the snow.

- Bitterly cold conditions are expected Sunday night through Tuesday morning with wind chills 15 below to 25 below zero possible Monday morning.

DISCUSSION

Issued at 257 PM CST Sat Jan 17 2026

An increasingly sheared mid-level trough axis above a sharpening low- level baroclinic zone has been able to wring out steady snow across southern Wisconsin through the day. The resultant axis of light snow with embedded transient bands of heavier snow has shifted into the northern tier of counties as the entire airmass pivots southeast. Where the synoptic snow is occurring, impacts have been fairly low per recent travel webcams. The band of light snow should continue its southeastward trek across northern Illinois through mid-evening before the remaining forcing from the trough and accelerating baroclinic/f-gen axis weaken and exit the area by late evening. With the loss of daytime heating and temps remaining steady in the mid teens, slippery conditions are expected to develop for areas north of I-80. Total accumulations around a half inch are possible, with localized swaths of around an inch north of I-88.

Meanwhile ahead of the main band of snow this afternoon and early evening, scattered light snow showers have been common with diurnal support. Dry low-levels have limited precip at the surface, with stratocumulus bases generally 3-4kft.

Behind the exiting synoptic snow this evening, shallow stratus firmly in the DGZ should persist through much of the night while producing on and off flurries.

Partly to mostly cloudy skies are expected Sunday morning as modest low-level WAA ensues. A low-amplitude trough currently over northern Alberta will strengthen while tracking toward the western Great Lakes through Sunday. Notable mid-level diffluence somewhat collocated with the left-exit of a 120 knot upper-jet will provide ample ascent for precip generation over the area mid-afternoon through mid-evening. Full top-down saturation will be the primary limiting factor for a more appreciable snow event, with questions how much of the robust snow aloft reaches the surface. Latest guidance supports totals around an inch over northern Illinois and northwest Indiana, though given the forcing noted above, would not be surprised to see the system overperform with higher totals if saturation is prevalent.

An arctic cold front will quickly cross the area Sunday evening, ushering in rapidly falling temps with WNW/NW gusts to 40-45mph. Some gusty snow showers will also be possible with the front. By daybreak Monday, the combination of temps around or slightly above zero combined with the strong winds will result in wind chill readings ranging from -15 to -25, lowest west of the Fox River Valley where a Cold Weather Advisory may be needed. Highs Monday will struggle to reach 10 degrees, with maximum wind chills remaining solidly below zero. Winds will begin to diminish Monday night as a surface high passes south of the area, but wind chills as low as -15 degrees can be expected Tuesday morning.

Kluber

Rather good consistency in the models and their ensembles for a brief moderation of temps Tuesday into Wednesday ahead of a clipper system moving across the Great Lakes region. High temps on Tuesday back in the 20s and possibly upper 20s/lower 30s on Wednesday. Still some uncertainty for precip chances across the local area Tuesday night into Wednesday morning with this clipper. Blended guidance now has chance pops for the northern half or so of the area and that seems reasonable for now.

There remains quite a bit of uncertainty for the end of next week into next weekend with the potential for an active pattern for or near the local area. While the ensembles still show a decent spread in possibilities, this time period has looked active for the past week. Regardless of whether precip develops for the local area, current trends favor a continued cold/very cold pattern. cms

AVIATION /00Z TAFS THROUGH 06Z MONDAY/

Issued at 603 PM CST Sat Jan 17 2026

Key Messages:

- A period of snow with IFR/MVFR visibilities will occur this evening.

- Another round of snow with IFR/MVFR visibilities is expected tomorrow afternoon and evening.

- MVFR ceilings will be observed through a large chunk of the TAF period.

- Winds will turn west-northwesterly and gust to around 30 kts behind an arctic cold front tomorrow night.

Steady, light snow will occur at the terminals this evening. MVFR to IFR visibilities will be observed, and around half an inch to locally near an inch of fluffy snow accumulation is expected before the steadier snowfall ends prior to midnight. Flurries may then continue through the night while MVFR/low-end VFR stratus remains overhead.

While the lower clouds should largely clear out by mid-morning tomorrow, another clipper-type weather system will dive into the region tomorrow afternoon, bringing another period of snow with IFR/MVFR visibilities and MVFR ceilings. Another half inch to an inch or so of dry/fluffy snow accumulation is expected with this round, with a lower-end chance for a localized 2" somewhere as well. This next round of steadier snowfall should conclude prior to midnight tomorrow night, but again, flurries may persist for several hours after the main wave of snow has ended.

Sustained westerly to southwesterly winds between 10 and 15 kts with gusts in the 20-25 kt range are expected through most of the TAF period. Winds will then shift more west-northwesterly late tomorrow evening behind an arctic cold front. Gusts near and in excess of 30 kt are likely to be observed for several hours after the frontal passage.

Ogorek

MARINE

Issued at 330 AM CST Sat Jan 17 2026

A gale watch remains in effect late Sunday night through Monday afternoon for the IL and IN nearshore waters.

An arctic cold front will move across the area Sunday night bringing much colder temperatures and strong winds to the region, with a period of gales expected late Sunday night through at least midday Monday. Freezing spray is also expected, especially for the IN nearshore waters. cms

HYDROLOGY

Issued at 253 PM CST Fri Jan 16 2026

The upcoming extended period of very cold temperatures will likely result in the rapid development of ice on area rivers and streams which may increase the chance of localized ice jam flooding. Last week's heavy rainfall has resulted in increased streamflow in several basins, including the Fox, Des Plains, and Illinois River basins. This higher streamflow will result in a greater potential for freeze up ice jam flooding.

- Izzi

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory until 9 PM CST this evening for Winthrop Harbor IL to Gary IN.

Gale Watch from late Sunday night through Monday morning for Winthrop Harbor IL to Gary IN.

Small Craft Advisory until 3 AM CST Sunday for Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.

Gale Watch from late Sunday night through Monday afternoon for Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.