textproduct: Chicago

KEY MESSAGES

- Snow, falling heavily at times with rates up to around an inch per hour, will affect areas near the lake through this evening. Lake effect will shift east from IL into IN by early evening and east of Porter County by around midnight.

- Snow will end away from lake Michigan by early evening.

- Dangerously cold wind chills expected late tonight and Monday morning.

UPDATE

Issued at 527 PM CST Sun Jan 25 2026

Have upgraded Lake County Indiana to a Winter Storm Warning through 8pm. Ongoing heavier LES combined with upstream trends with the dominant LES band over western Lake Michigan suggest that consolidation of the LES is ongoing into a more formidable band early this evening. While this was expected, trends toward a longer residence time of the band (up to two hours), locally higher winds in the heart of the band, and a highly traveled corridor support the upgrade to a warning. Snowfall rates in the main band will likely exceed 2"/hr as much of the convective layer and associated ascent reside in the DGZ. Area webcams also show that efficient snowflake generation is ongoing with aggregation also present.

Kluber

DISCUSSION

Issued at 232 PM CST Sun Jan 25 2026

Back edge of the synoptic snow is moving east across the area this afternoon and should continue eastward with snow ending from east to west through early evening. Lake enhanced snow will transition to pure lake effect snow by early evening as the synoptic snows move off to the east.

Recent ACARs soundings out of MDW depict a sharp inversion around 5kft, so lake induced instability is shallow, but very strong. Aided by the synoptic snows, the lake enhanced snow this morning has been fallen heavily at times with snowfall rates up to an inch per hour. Lake enhanced snow has penetrated as far inland as Kankakee County, though anticipate the inland penetration and probably the intensity of the snow will decrease a bit as the seeder-feeder process ends as synoptic snows shift east.

Any potential decrease in intensity of the lake effect looks to be short lived early this evening as mid-upper level trough approaches this evening. Height falls in advance of the trough are progged to result in rising inversion heights and deepening lake induced convective layer. In addition to the rising inversion height, the nocturnal strengthening of the land breeze convergence zone should lead to the development of an intense narrow band of heavy lake effect snow as the focus shifts east into Porter County.

Lake effect parameters are forecast to become exceptionally favorable for a very intense lake effect snow band, with the main question for our CWA being how quickly it organizes and intensifies. By late evening and especially after midnight, it wouldn't be at all surprising to see 2-3"+ per hour snowfall rates with the band. The potential ramp up in intensity of the lake effect band looks to occur far enough west to justify the earlier upgrade of Porter County to a winter storm warning and bumping up snowfall totals there. The ceiling is high with this event, should the band intensify on the earlier end of the spectrum and particularly if it were to slow its progression across Porter County, then double digit additional snowfall totals would be possible. On the other end of the spectrum, if the band were to remain more progressive and the intensity were to not take off until it is east of Porter County, then the additional snowfall amounts in northern Porter County could end up more in the 2-4" range.

In the wake of the snow, skies will clear out and with many areas now covered in a fresh blanket of fluffy new snow, would anticipate temps to respond nicely to the cold air advection. Made no significant changes to temps tonight, but did nudge high temps down a bit for Monday. Northwest winds 10-15 mph should send wind chills down 15 to 25 below zero late tonight into Monday morning, so Cold Weather Advisory looks to be in good shape with no changes planned.

- Izzi

Monday night through Saturday: Issued at 340 AM CST Sun Jan 25 2026

The next robust clipper system will descend out of Saskatchewan on Monday and then across the Upper Great Lakes region Monday night into Tuesday morning. Seeing generally good agreement on the handling of this feature, with guidance taking the core of the most robust mid-level height falls to our north. That said, the magnitude of large scale forcing is quite robust.

While guidance doesn't appear to formally produce snow accums in our area, forecast soundings from various guidance would support flurries or light snow with saturation down under 850-900 mb, particularly late Monday night through Tuesday morning across roughly the northeastern half of the CWA and especially across far northeast Illinois. Thereafter, steepening 0-1 km lapse rates in the wake of the associated surface front look to drive increasing saturation into the base of a fairly deep dendritic growth zone late Tuesday morning and afternoon. Low-level f-gen is generally transient or non- existent, suggesting the threat for bonafide squalls is low, but seeing a signal of NW-SE oriented streaks of QPF in some of the guidance which is likely indicative of isolated-scattered gusty snow showers through Tuesday morning and early afternoon. At this time, have not formally added a snow shower mention to the grids, but if trends continue, will need to consider a weather mention during this time frame. Can't totally rule out some disorganized LES meandering into far NE Porter County Tuesday afternoon given slightly more NW oriented boundary layer flow, but the bulk of any lake effect looks to remain decidedly to our east.

A reinforcing shot of cold air will send low temperatures Tuesday night back to either side of 0 degrees with colder wind chills given a steady westerly breeze.

The next robust disturbance arrives late Tuesday night into Wednesday. Guidance appears to be settling in on a slightly farther south track at this point, although there's generally low confidence this far out with these types of systems. Will be a period to watch as this would be another instance of light snow accumulations falling into a very cold airmass where road treatments would likely be mostly ineffective. Strongest signal for light snow accumulations into Wednesday afternoon are roughly south (to well south) of I-80.

Lots of spread in the handling of the general large scale synoptic pattern by the end of the week. Still seeing a signal (ephemeral as it may be from run-to-run) of a potentially interesting set up towards Thursday night - Friday involving an intense shortwave trough pushing southwestward across the Great Lakes which would turn the lake effect snow machine back on in the general region.

Otherwise, continued cold is the message through next week. Could be some periods where we're flirting with Cold Weather headline criteria at times, but nothing to the level of what we experienced this past Friday/Saturday.

Carlaw

AVIATION /00Z TAFS THROUGH 06Z TUESDAY/

Issued at 538 PM CST Sun Jan 25 2026

The lake effect snow will continue to push eastward with time this evening, ending at GYY within the next few hours. Otherwise, a flurry or two may fall through the overnight hours as a stratus deck meanders through the region. Based on the current back edge of the stratus over southeastern Wisconsin, would expect clearing to take place sometime before daybreak Monday in line with the passage of the cyclonic shear axis of the departing upper-level trough. Winds will remain northwesterly through the night.

There may be an opportunity for clear skies during daylight hours tomorrow as winds gradually back westerly and eventually southwesterly through the afternoon. Upper-level clouds will thicken during the evening in advance of a clipper system tracking through the Upper Great Lakes. In fact, a period of LLWS may materialize tomorrow night as flow at 2000 feet increases to 50-55kt.

Borchardt

HYDROLOGY

Issued at 230 PM CST Fri Jan 23 2026

River gauges, reports from local officials, and reports from trained ice spotters continue to indicate a few ice jams across the area due to the significant increase in river ice over recent days. With continued cold weather into next week, conditions will remain favorable for river ice formation. While no widespread flooding is expected, localized ice jams may occur.

- NWS Chicago

LOT WATCHES/WARNINGS/ADVISORIES

IL...Cold Weather Advisory from midnight tonight to noon CST Monday for ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011- ILZ012-ILZ013-ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033- ILZ039-ILZ103-ILZ104-ILZ105-ILZ106-ILZ107-ILZ108.

Winter Storm Warning until 6 PM CST this evening for ILZ104- ILZ105.

Winter Weather Advisory until 6 PM CST this evening for ILZ023- ILZ108.

IN...Cold Weather Advisory from midnight CST /1 AM EST/ tonight to noon CST /1 PM EST/ Monday for INZ001-INZ002-INZ010- INZ011-INZ019.

Winter Storm Warning until 8 PM CST this evening for INZ001.

Winter Storm Warning until midnight CST tonight for INZ002.

Winter Weather Advisory until 9 PM CST /10 PM EST/ this evening for INZ010-INZ011-INZ019.

LM...Small Craft Advisory until 6 PM CST Tuesday for the IL and IN nearshore waters.