textproduct: Chicago

KEY MESSAGES

- Another Arctic frontal passage later today will usher in an extended period of dangerous cold temperatures late tonight into the upcoming weekend.

- An Extreme Cold Warning is now in effect late tonight through Friday morning for areas near and north of I-55 where wind chills are expected to drop between -30 to -40F. A Cold Weather Advisory in effect for remaining areas where wind chills may drop between -20 to -30F.

- Fluffy accumulating snow paired with cold temperatures may cause hazardous travel conditions late Saturday into Sunday.

UPDATE

Issued at 1115 AM CST Thu Jan 22 2026

No big changes to the forecast this morning, but extended the Cold Weather Advisory for our SE CWA through 15z Saturday and tacked on a Cold Weather Advisory to the end of the Extreme Cold Warning and also ran that advisory through 15z Saturday.

Small patch of some stratocu over NW IL has had a few flurries with it, so certainly plausible that there would be a few flurries at times this afternoon, mainly near the WI border. This stratocu deck has some horizontal convective rolls in the strong cold air advection tonight will remain prone to occasional flurries as clouds are in cold enough layer for ice nuclei to be present. Very common for flakes to leak from stratocumulus in bitter cold air masses like the one that comes in tonight.

We're taking a close look at incoming model data and will have an update on snow chances this weekend this afternoon.

- Izzi

DISCUSSION

Issued at 330 AM CST Thu Jan 22 2026

Through Friday Night:

Focus through the end of the workweek remains the potential for dangerous cold returning late tonight as surface high pressure expands across the region in the wake of another Arctic front.

Snow showers have shifted east of the area early this morning with mostly clear skies and cold air advection allowing temperatures to steadily drop into the teens. Winds will remain breezy through the remainder of the daytime hours with gusts in the 25 to 35 mph range making for a cold and blustery Thursday. Sporadic gusts up to 40 mph can't be ruled out during the afternoon and early evening.

The second of two Arctic fronts is currently moving into Minnesota and will usher in our next round of bitterly cold temperatures and dangerous wind chills as it moves across the area later today. There are patches of stratus across portions of IA, WI, and MN ahead of and behind the front that are producing flurries and even a few snow showers given the cold airmass in place. As these clouds shift southeast over the area can't rule out isolated snow showers and flurries here locally during the late morning through the early evening timeframe. Still not expecting notable accumulations from this, perhaps at most a very localized light dusting and brief reductions in visibility when paired with the gusty winds.

While winds are expected to ease slightly this evening they will remain breezy through the night into early Friday morning. This paired with steadily dropping temperatures will lead to wind chills dropping into the -20 to -40F degree range across the area, coldest across interior northern Illinois. Have upgraded the Extreme Cold Watch to a Warning with this update and issued a Cold Weather Advisory for remaining portions of east central Illinois and northwest Indiana. Given how sensitive wind chill values are to wind speed and air temperature once it gets this cold, some uncertainty on the degree of cold exists due to continued model spread on how cold the air temperatures end up. Have maintained a blended approach for now since it properly captures the message that dangerous cold will occur late tonight through Friday morning. In fact, wind chills may remain near and below 20F through Saturday morning for areas north of I-55 where a follow-up Cold Weather Advisory will likely be needed once the warning expires.

Lake effect snow showers likely develop across portions of northwest Indiana into Friday as the colder airmass paired with north northwesterly fetch sets up across Lake Michigan. Given a signal for weak convergence developing amidst expansive surface high pressure, have increased snow shower chances accordingly for northeast Porter County where accumulating snow will be possible. The band may shift west into Lake County late Friday night through confidence in this distance is on the lower side.

Petr

Saturday through Wednesday:

The primary concern and challenge is the potential for accumulating snow Saturday through Sunday night along with the chance for lake enhancement across far northeast IL.

High pressure will be slowly weakening as it moves across the Great Lakes region Saturday into Saturday night. With the warmer waters of Lake Michigan, the models try to develop a lake effect snow band Friday night as convergence develops that may persist into Saturday morning. Low confidence for how much may actually develop as well as low confidence for it reaching land but blended slight chance pops for northeast IL Saturday morning seem reasonable for now for this potential.

The local area will then be on the northern edge of a winter storm affecting much of the eastern half of the country this weekend. Over the past 24-48 hours the models and their ensembles have made a decisive shift north with the precip shield, which will be all snow here. While confidence is slowly increasing, there still remains uncertainty for specifics. The ECMWF and its ensembles remain in very good agreement with snow spreading across the area during the day Saturday and then continuing into Sunday for a long duration snow event. The GFS is further south with its ensembles about 50/50 for snow for the local area. Canadian is roughly in between the ECMWF/GFS. How much precip that can make it this far north is still in question given the large swath of heavy qpf expected further south. An upper level trough will also be digging across the Plains Sunday and shifting east Sunday night. The speed of this trough could play a large role in how far north the snow is able to spread. If the snow does spread across the entire area, there would then be the potential for lake enhanced snow across far northeast IL, possibly shifting east into northwest IN Sunday night as it ends.

With all of the above in mind, the blended pops have increased into the likely range for Saturday night/early Sunday morning, mainly southeast of I-55 and this seems reasonable at this time. Too early for any amounts but snow ratios will be high and likely dependent on forcing. Made no changes to the blended ratios of 20 to 1 which also match WPC. But should a ECMWF solution pan out, with more qpf and better forcing, then higher snow ratios may materialize.

The pattern will continue to favor cold/very cold temps through the middle of next week with a re-enforcing blast of cold air on Monday with wind chills in the 10 below to 20 below zero range Monday morning. Highs may try to get into the 20s Tuesday with another possible blast of cold air midweek. cms

AVIATION /18Z TAFS THROUGH 00Z SATURDAY/

Issued at 1132 AM CST Thu Jan 22 2026

Aviation forecast concerns for the 18Z TAFs:

- Strong west-northwest winds with gusts around 30 kts into tonight.

- Chance of flurries/snow showers mainly this evening.

A surface trough will move east across the terminals early this afternoon, producing a subtle wind shift to the west-northwest with gusts approaching 30 kts. A few flurries may squeeze out of a VFR stratocu deck along/ahead of the front, though these are expected to be inconsequential and rather spotty per upstream observations.

A stronger arctic cold front will push east across the terminals this evening, accompanied by a mid-level disturbance. This will further shift winds to the northwest, with a period of 30-35 kt gusts behind the front into the overnight hours. A slightly deeper layer of low-level moisture along/ahead of this front may support scattered flurries/snow showers, some of which could produce brief MVFR visibilities and perhaps a dusting of snow accumulation. More shallow high-end MVFR/low-end VFR strato cu may produce additional inconsequential flurries overnight.

Northwest winds will gradually ease late tonight into Friday, with decreasing coverage of low-level cloud cover as a very cold arctic high pressure system builds into the area.

Ratzer

HYDROLOGY

Issued at 258 PM CST Mon Jan 19 2026

Area hydrographs and ice spotter reports confirm that ice continues to develop and spread across areal rivers. Localized ice jams are already present along the Rock, Des Plaines, and Fox Rivers. Continued cold temperatures tonight and Tuesday will cause ice to continue expanding and thickening.

After a brief warm-up in temperatures to above 20 degrees on Tuesday-Wednesday, another push of bitterly cold temperatures will arrive Thursday night. As a result, the threat for ice jams including localized flooding will increase further toward the end of the week and through the weekend.

- NWS Chicago

LOT WATCHES/WARNINGS/ADVISORIES

IL...Extreme Cold Warning from 3 AM to noon CST Friday for ILZ003- ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013- ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ103-ILZ104-ILZ105- ILZ106-ILZ107-ILZ108.

Cold Weather Advisory from noon Friday to 9 AM CST Saturday for ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011- ILZ012-ILZ013-ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ103- ILZ105-ILZ106-ILZ107-ILZ108.

Cold Weather Advisory from 3 AM Friday to 9 AM CST Saturday for ILZ033-ILZ039.

Cold Weather Advisory from noon to 1 PM CST Friday for ILZ104.

IN...Cold Weather Advisory from 3 AM CST /4 AM EST/ Friday to 9 AM CST /10 AM EST/ Saturday for INZ001-INZ002-INZ010-INZ011- INZ019.

LM...Gale Warning until 3 AM CST Friday for the IL and IN nearshore waters.

Small Craft Advisory from 3 AM to 3 PM CST Friday for Winthrop Harbor IL to Gary IN.

Heavy Freezing Spray Warning from 9 PM this evening to 3 PM CST Friday for Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.

Small Craft Advisory from 3 AM Friday to 3 AM CST Saturday for Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.