textproduct: Chicago

KEY MESSAGES

- Accumulating snow will continue to result in hazardous travel conditions today, mainly near Lake Michigan and south/east of the I-80/I-55 corridors.

- Locally heavier snowfall rates of 1+"/hour are possible with the lake enhanced/lake effect snow.

- Another period of very cold conditions will occur late tonight/early Monday morning with wind chills between 20 and 25 below zero.

DISCUSSION

Issued at 340 AM CST Sun Jan 25 2026

Through Monday:

The national radar mosaic this morning is a sight to behold with a massive swath of precipitation extending from near the Mexican border and Gulf Coast up through the Mid-Atlantic. The northern periphery of the gargantuan precipitation shield extends into our forecast area, with roughly the southeastern half of our CWA observing steady, accumulating snowfall at this time.

Snowfall rates across our southeastern CWA should pick up a bit over the next few hours as an approaching southern stream trough and an increasingly coupled jet structure enhance lift through an exceptionally deep dendritic growth zone. However, with the strongest forcing focused primarily above the DGZ, rates here should still only peak at maybe a little more than 0.5"/hour. With the synoptic snow shield still slated to peel away from west to east this afternoon, our forecast of 4-7" dry/fluffy storm total snow accumulations for our southeastern counties with a sharp gradient farther to the northeast thus still appears to be on track. Therefore, not planning to make any changes to the going Winter Weather Advisory there with the main message still being a period of continued hazardous travel conditions.

Meanwhile, the Arctic air mass in place over a Lake Michigan with water temperatures in the 30s has allowed for lake enhancement to occur into Cook County, with a more bona fide lake effect snow band with embedded mesovortices extending northward from Lake County, IL up a long ways along the southeast Wisconsin lakeshore at press time. Earlier last evening, snowfall rates to around 1"/hour were observed within the heart of this lake effect band, and would suspect that similar rates may continue to be observed while the band sits near the Illinois lakeshore. However, the band has been struggling to penetrate much more than a few miles inland (possibly due to the extensive ice coverage in our nearshore waters), and as such, widely varying snowfall totals will likely be observed over the span of just a few miles with lower totals occurring farther away from the lake.

The overall trend for this band should be for it to remain along or just offshore the southwestern Lake Michigan shoreline for several more hours this morning before its primary convergence axis eventually drifts back southward towards Cook County and then shifts into northwest Indiana, with the band's momentum at this point allowing it to penetrate farther inland after it reaches Lake and Porter counties in northwest Indiana. For the time that the band stays parallel to the shoreline, its precise evolution will be difficult to predict beyond 1-2 hours. However, if it manages to sit over the same location for several hours, then would not be surprised to see some highly localized 6+" totals be observed. Though, with this still being an item of lower confidence (and since the spatial footprint of these higher totals should be quite small and confined to within a few miles of the lakeshore), will continue to hold off on issuing a Winter Storm Warning for Lake and Cook counties in Illinois.

Did give stronger consideration to upgrading Porter County to a Winter Storm Warning as it looks like there could be a pretty good 1-3 hour long or so thump of lake effect snow there this evening with strong omega progged beneath the 7000 ft AGL inversion as the band shuffles eastward across the county. Snowfall rates may peak in excess of 1"/hour during this time, which could add a quick few inches on top of the earlier system snow accumulation, in addition to making travel more difficult. Didn't quite have enough confidence in snowfall totals there getting much higher than elsewhere to pull the trigger on a warning upgrade at this time, but will pass my concerns along to the day shift.

Lastly, northerly winds will strengthen during the day today, then turn northwesterly this evening, ushering in another period of cold air advection. With clouds likely to largely clear out in most spots for tonight as well, temperatures are likely to fall back below 0F across most of the area once again into Monday morning. The blustery northwest winds will help yield minimum wind chills of -20 to -25F across most of the area late tonight into Monday morning, so have issued another area-wide Cold Weather Advisory to highlight this.

Ogorek

Monday Night through Saturday:

Monday morning will start out cold and brisk with a steady WNW/NW breeze which, when combined with air temperatures in the single digits, will lead to wind chills in the 15 to 25 below range through the bulk of the morning. See the short term section above for specifics on the cold weather headlines. With a robust shortwave directly overhead to start the day, can't rule out a few flurries through the morning and possibly in the afternoon depending on the expansiveness of any lingering stratus. The signal for flurries isn't particularly robust, however, so have not added a mention to the grids at this point.

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 /12Z TAFS THROUGH 18Z MONDAY/

Issued at 542 AM CST Sun Jan 25 2026

Snow will continue at the Chicago-area terminals today. Generally prevailing IFR vsbys are expected at ORD, MDW, and GYY, with more intermittent IFR conditions at DPA. Currently, lake enhancement is somewhat disorganized, but may become a bit better organized through the morning. Potential exists for vsbys to briefly drop under 1 mile at times at ORD, MDW this morning and early afternoon before activity ends from NW to SE. Continue to show period of LIFR conditions at GYY where the signal for heavier lake effect exists this afternoon. At RFD, flurries will be possible this morning, and perhaps persisting into the early afternoon.

Winds at ORD/MDW are expected to largely remain N to NNW today, but at MDW may occasionally flip NE at times. Winds at GYY will be easterly and will slowly turn northerly through the day. Gusts will increase this afternoon and snow comes to an end, and will likely persist into the evening and Monday morning.

Carlaw

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 Weather Advisory until 6 PM CST this evening for ILZ006- ILZ013-ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039- ILZ103-ILZ104-ILZ105-ILZ106-ILZ107-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 Weather Advisory until midnight CST tonight for INZ001- INZ002.

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

LM...Small Craft Advisory from 9 AM this morning to 6 PM CST Tuesday for Winthrop Harbor IL to Gary IN.

Small Craft Advisory from noon today to 6 PM CST Tuesday for Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.