textproduct: Chicago

KEY MESSAGES

- Southwest winds turning northwest this morning with gusts around 30 to 35 mph. Some blowing and drifting snow possible.

- Isolated to scattered gusty snow showers this morning, mainly north and east of a Rochelle to Rensselaer line. Flurries then possible through the afternoon area-wide.

- Cold conditions will continue into the weekend with mainly subzero wind chills through Saturday morning.

- Threat for impactful lake effect snow for northeast IL and northwest IN Thursday night through Saturday night.

DISCUSSION

Issued at 241 AM CST Tue Jan 27 2026

Early-morning objective analysis places a roughly 1004 mb surface low just northeast of Lake Superior with an attendant cold front slicing across Wisconsin and just about to cross into northwest Illinois. A concentrated area of gusty snow showers continues to track steadily south and east out of southwest Wisconsin immediately along and just behind the aforementioned frontal boundary. Latest guidance is generally doing a poor job handling the degree of boundary layer moistening which is obviously receiving a boost from the notable large scale dynamics associated with the parent upper-level wave. Have introduced chances for snow showers mainly north and east of a Rochelle to Rensselaer line through about mid morning.

Timing out the salient upstream features brings initial snow showers south of the WI state line in the 4-6 AM window, and then south and eastward across the region through mid morning. These initial snow showers, which are aligned within NW-SE horizontal convective rolls do not look particularly robust and organized at this time. This matches the environmental parameter space, with generally limited low-level instability and relatively thin and scattered-looking cloud cover. A somewhat more organized cluster of snow showers with reflectivities nearing 25-30 dBZ at times from the La Crosse, WI radar along the main frontal boundary may persist into the region this morning. Latest timing brings this to the state line just after 6 AM, into the Chicago area through 7 to 8 AM, and then across parts of NW Indiana through 8 to 10 AM. With the snow squall parameter space not particularly robust, fast forward motions limiting residence and accumulation time, and visibilities generally remaining above one mile upstream, not terribly concerned with a true snow squall issue this morning as this activity tracks overhead, but will message the potential for gustier snow showers which could lay down a quick dusting/light coating in spots through the morning rush hour.

As the main front sweeps through, northwesterly winds will increase with gusts briefly around 35 mph before easing into the 25-30 mph range this afternoon. Intermittent flurries will be possible within any lingering scattered to broken stratus layer, but guidance indicates we should steadily lose the bulk of the BL moisture through late afternoon and evening, which should bring any lingering flurry/snow shower potential to an end. The one exception will be near the lake as colder air spills into the region this afternoon. As this occurs, the main lake effect snow shield will build westward a bit. While the vast majority of LES will remain east of our region given the largely WNW/NW boundary layer flow, it's possible that some flurries or light snow develops as far west as parts of northeast Porter County this afternoon and evening.

Conditions look quiet tonight. Depending on temperature trends, it's possible some spots could flirt with the 20 below advisory criteria, but this currently does not appear long-lived and widespread enough to warrant the issuance of another Cold Weather Advisory into Wednesday morning at this time.

On Wednesday, the next shortwave trough will sweep across the Great Lakes. The trend towards a generally drier outcome persists tonight, with no indications of an accumulating snow threat in our area into Wednesday night, with the main axis of deeper saturation pushed well to our south.

The main focus during the end of the week and into the upcoming weekend remains on the potential for another round of accumulating lake effect snow (potentially a long-duration event) as another sprawling ~1050 mb arctic high descends out of Saskatchewan and Manitoba late Thursday night into Friday. As this occurs, 850 mb temperatures are forecast to drop to around minus 20 C, which in turn will result in building inversion heights over the lake. LES parameters certainly look sufficient to support periods of more intense lake effect snow, with lake- induced ELs nearing 9-10 kft at times, especially through Friday with 850 mb temps forecast to warm through Saturday.

Initial LES looks to develop late Thursday night into early Friday morning. It's possible that this initial activity has a somewhat difficult time organizing given some degree of wind shear in the boundary layer as a synoptic scale trough pivots southwest out of the Upper Great Lakes. By later Friday night and Saturday, however, guidance depicts generally lessening shear as the bulk of the atmospheric flow shifts northeasterly. Guidance then depicts LES organizing into a single dominant band during this time as low-level convergence maximizes down the long axis of the lake. During this time, ELs are forecast to fall a bit as 850 mb temps warm, which may have a bit of a modulating effect on LES intensity. That said, given the progged increasing convergence, even 6-7 kft ELs will be more than sufficient to support periods of heavier snowfall.

At this point, it remains too early to hone in on specifics, but guidance trends continue towards an impactful period of lake effect snow in our area, including Chicago, parts of NE and east-central Illinois, and NW Indiana from late Thursday night through Saturday night, and possibly even through Sunday. Guidance at this time does indicate the potential for quite a bit of band wobbling, which in turn could limit residence times and overall totals, but a more quasistationary north-south oriented band is also advertised (CMC, UKMET for example). Temperatures in the teens and single digits will have the potential to exacerbate impacts due to a very light/fluffy snow and lessened effectiveness of road treatments.

Beyond this weekend, there's another signal for another period of light accumulating snowfall early next week.

Carlaw

AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 1100 PM CST Mon Jan 26 2026

Breezy southwest winds with gusts occasionally exceeding 30 kt will continue through the overnight hours in advance of an approaching cold front. Isolated patches of drifting and blowing snow may occur at ORD/MDW/GYY through the overnight hours, particularly on west to east oriented runways.

Toward daybreak, a cold front will sweep across the terminals with a west to northwesterly wind shift. A few snow showers are present along the front across southeastern Minnesota at press time. Forecast model guidance is not handling the activity well, leveraging lower than average confidence in evolution going forward. Should the snow showers hold together into northern Illinois, a brief drop in visibility to 2-3SM may occur (looking at the 11-14Z timeframe from northwest to southeast across the airspace). Did consider introducing PROB30 groups at the terminals for this activity, but opted to hold off for now in favor of watching trends. Snow showers or not, MVFR stratocu will spread over the terminals behind the front as northwest winds routinely gust around 30kt. A flurry or two may fall out of the MVFR deck from time to time, as well.

Wind magnitudes will quickly drop off after sunset and back modestly toward the west or even southwest. MVFR cigs are expected to gradually scatter after sunset, as well, but may hold on as late as 03-05Z until the back edge of the upper-level cyclonic shear axis spreads overhead.

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...None. IN...None. LM...Small Craft Advisory until 6 PM CST this evening for the IL and IN nearshore waters.