textproduct: Chicago

KEY MESSAGES

- A light coating to half inch of snow is likely (70%+ chance) tonight into early Monday morning.

DISCUSSION

Issued at 212 PM CST Sun Feb 1 2026

Mid and high-level cloud cover continues to increase from west- to-east in association with our next weather system shifting eastward across the Mississippi Valley early this afternoon. An area of light snow has also developed west of the area through the morning within a region of deeper moisture and isentropic upglide. While this area of light snow is attempting to shift eastward into western IL at this time, it is also fighting against drier air below 10,000 feet across northern IL. Accordingly, it is going to take time for the snow to make eastward extent into the Chicago metro area this evening, likely not onsetting here until sometime after 8 or 9 this evening. Even after it starts snowing this evening, rates are expected to remain light, owing to rather poor forced ascent and only modest moisture in the DGZ. So, why the potential for snow tonight is high (70%+), the poor snow quality (small flake sizes) and light rates is not going to amount to much (only a light coating to as much as one half inch). The light snow is expected to end prior to daybreak Monday morning for most.

Forecast soundings overnight indicate poor moisture in the DGZ for a period, which suggests there to be a low, but non-zero, chance for some light freezing drizzle. While the possibility for this cannot be total ruled out, cloud temperatures may remain just cold enough (~-10C) to keep any lingering light precipitation in the form of low quality snow flakes overnight. Also, the window for this possibility also looks limited to only a couple hours at any given location. For these reasons, we have opted to keep the mention out of the forecast at this time.

Aside from the chance of a few occasional flurries from a lingering strato cu deck on Monday, conditions will remain quiet, with highs in the mid to upper 20s.

Late Monday night through early Tuesday morning, eyes will be on the next mid-level impulse expected to drop southeastward along the lower-level baroclinic zone draped from the Dakota's into the Midwest. As it does, we could experience another coating of snow sometime late Monday night into to early Tuesday morning. The NBM did not offer up any POPs for this period, but in collaboration with neighboring offices, we opted to add a slight (20%) chance for some light snow late Monday night. At the present time, we have only added this chance to northwestern parts of IL. Admittedly, however, we could see the need for these chances to be expanded into much of northern IL with future forecast updates. Otherwise, the main chances for snow later Tuesday with this wave are expected to quickly transition to our southeast across the Ohio Valley.

A rather marginal lake-effect snow set-up into northwest Indiana and along the Illinois shore will then be the next focus for precip Tuesday night into Wednesday morning. Low inversion heights and borderline thermo profiles indicate the precip will be limited to isolated to scattered light showers. We have maintained the going chance PoPs with little accumulation during this window.

Broader northwest flow will persist midweek through next weekend. Temps will moderate to above freezing on Thursday, and Friday, which would be the first time in around three weeks for much of the area. This would also come with a potential for more active weather in the region late in the week, with chances of accumulating snow and perhaps mixed precip. Another period of colder conditions then appears to be in store for next weekend.

KJB

AVIATION /00Z TAFS THROUGH 06Z TUESDAY/

Issued at 540 PM CST Sun Feb 1 2026

Forecast concerns for the terminals...

- Period of snow tonight resulting in reduced visibilities and some accumulation.

- MVFR ceilings to persist into Monday morning before improving to VFR Monday afternoon.

A shortwave trough continues to pivot out of the Upper Midwest towards northern IL which has developed an area of snow across eastern IA and southern MN. While the light radar echoes over northern IL have resulted in some occasional flurries, the true accumulating snow with reduced visibilities is still near the Mississippi River and won't reach the terminals until 03-05z, earliest at RFD. Once the snow arrives expect a few hour period of MVFR to IFR visibilities (2-3SM) before snow starts to push east and transitions more to light snow and flurries for the rest of the overnight hours. Given progressive nature and modest snow rates, accumulations look to generally be less than 0.5 inches for this event.

Heading into Monday, the light snow/flurries will gradually come to a close by mid-morning. However, MVFR ceilings are expected to prevail through the late morning hours before attempting to lift back to a 3000-4000 deck. How quickly ceilings returns to VFR remains a bit uncertain but didn't see any reason to alter the prevailing time in the TAFs at this point. Regardless, ceilings should continue to lift through Monday afternoon so VFR conditions are expected by the end of the TAF period. Otherwise, expect south-southwest winds tonight to become more west- northwest Monday morning with speeds remaining around 10-12 kts.

Yack

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...None.