textproduct: Chicago

KEY MESSAGES

- Cold Weather Advisory in effect this morning for wind chills around 20 below.

- Slight chance for light snow northeast of about I-90 tonight. Turning blustery Tuesday with a small chance for a few snow showers.

- Cold conditions continue through the week with mainly dry conditions. Monitoring another potential for lake effect snow during the Thursday night - Saturday timeframe.

DISCUSSION

Issued at 213 AM CST Mon Jan 26 2026

A sprawling 1040-ish mb arctic high building across the Great Plains has brought an end to our accumulating snowfall and at the same time is ushering in a renewed push of cold air. Temperatures at this hour are wandering down below zero across interior northern Illinois and into the single digits above zero elsewhere. While low-level cold advection is ongoing, a persistent region of stratus across far northeast Illinois and northwest Indiana is muting the temperature fall a bit. Based on latest satellite and guidance trends, it does look like we'll largely lose this area of cloud cover through daybreak or so, but the delayed scattering may result in slightly "warmer" temperatures in spots. Regardless, a steady northwesterly breeze around 15 mph will result in morning wind chills in the 20 to 25 below range northwest of about I-55 and in the 15 to 20 below range elsewhere (NW Indiana in particular). No changes planned to the current Cold Weather Advisory.

Quiet but cold conditions are expected today as shortwave ridging briefly builds in overhead. A fast-moving and intense clipper system will push across the Upper Great Lakes tonight and Tuesday morning. Mid-level heights falls on the order of 120 meters/12 hours are forecast to spread across parts of northern Wisconsin and lower Michigan, highlighting the robust nature of large scale forcing accompanying this system. A significant layer of dry air is forecast to be in place across the local region, however, which should generally limit the snowfall threat across our area. That said, forecast soundings reveal effective saturation occurring down to around or under 850 mb late tonight during a brief window across the northeast half of the CWA, and the latest GFS is now cranking out a little QPF north and east of I-90. Given the intense forcing, have elected to introduce a slight chance for snow late tonight/early Tuesday morning in this region. The window for any snow will likely be brief (2-3 hours or less), and it's still possible dry air wins out, but did not feel comfortable with a completely precip-free forecast given the dynamics at play.

Increasing warm advection in advance of this system will facilitate a gradual uptick in southwesterly winds this evening and overnight. This in turn will eventually result in steady to slowly-rising temperatures overnight. Prior to this, air temperatures could briefly fall back into the negative single digits in spots this evening, particularly across our far southeast locales closer to the deeper snow pack which, when combined with the increasing winds, may result in wind chills briefly as cold as 20 below. Given the currently-expected brief nature of these wind chills, did not issue another cold headline given the anticipated "warming" overnight and through daybreak Tuesday. With the increasing winds, some patchy blowing snow may occur in open/rural areas within the deeper snowpack. It's possible that things have started to crust over a bit by tonight, but did add some patchy blowing snow (probably will be more like low drifting) wording to the grids for areas south of the Kankakee River where reports of 3 to 4 inches were commonplace from yesterday's system.

A reinforcing cold front will sweep through the area during the morning on Tuesday. Increasing cold advection may mute the diurnal temperature rise, and it's possible our current highs are a smidge too warm depending on the magnitude of cold advection. Increasing 0-1 km lapse rates should result in an expansion of low stratus through the morning and into the afternoon. Did contemplate adding some chances for snow showers, but have held off for now given the still marginal-looking nature to progged boundary layer moisture, which looks better across southern Wisconsin. Noting that the recent ECMWF is depicting some NW-SE oriented streaks of light QPF into the region during this timeframe, so something to consider in future forecast issuances given significant DCVA overhead.

On Wednesday, the next disturbance is slated to press across the region. The trend over the last few model cycles has been towards a bit of a drier and farther south outcome, with less modeled precip. Still somewhat skeptical of a completely dry outcome given the upper jet forcing and degree of mid-level saturation, but given the very limited signal across the ensemble suite, have left the NBM-delivered dry conditions as is.

Beyond this, the signal for an expansive upper trough cutting south and westward across the Great Lakes continues to grow in the guidance suite towards the end of the week. With this occurring as another 1050s mb arctic high builds southward across the north-central CONUS, the potential for another round of lake effect snow is evident from about Thursday night through Saturday. With ice cover likely to expand with time, it's a bit unclear how this might impact surface fluxes, although latest GLERL ice forecasts indicate ice coverage likely won't extend beyond 15-20 miles, with a wide open fetch available along the long axis of the lake. With the colder lake temperatures, thermodynamics are not off the charts, but certainly more than sufficient for intense lake effect with surface-850 delta Ts near 20 C and lake-induced ELs just under 9-10 kft. Way too much uncertainty at this time range to make any adjustments to the blended slight chance PoPs, but this will be a period to keep a close eye on.

Carlaw

AVIATION /06Z TAFS THROUGH 12Z TUESDAY/

Issued at 1059 PM CST Sun Jan 25 2026

Various VFR stratus decks based near 5kft and 8kft will ebb and flow over the airspace through the overnight hours, perhaps lasting longest at Lake Michigan-adjascent terminals. An occasional flurry or two may occur beneath either deck as well, particularly near ORD/MDW. Winds will remain out of the northwest through the overnight hours with a gust up to 20 kt or so from time to time.

As a surface high pressure system slides southeastward from the northern Plains to the Lower Mississippi River Valley today, the low-level pressure field across the Lower Great Lakes will gradually reorient to enforce winds shifting toward the west and eventually southwest. A gust or two to 20kt may occur during the afternoon hours. Largely sunny skies are expected during daylight hours, though a few stratocu clouds based near 1.5kft may develop over the new snowpack near ORD/MDW/GYY.

After sunset, southwesterly winds will increase in magnitude as the pressure gradient tightens ahead of a clipper system racing into the Upper Great Lakes. A period of LLWS is expected between 03- 09Z as southwesterly flow at 2kft increases to 50-55kt. A cold front with an associated west/northwesterly wind shift will race across the airspace during the early morning hours of Tuesday, perhaps accompanied by a snowflake or two.

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 until noon CST today for ILZ003-ILZ004- ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ019- ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ103-ILZ104- ILZ105-ILZ106-ILZ107-ILZ108.

IN...Cold Weather Advisory until noon CST /1 PM EST/ today for INZ001-INZ002-INZ010-INZ011-INZ019.

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