textproduct: Chicago

KEY MESSAGES

- A period of light snow accumulations are likely (60%+ chance) tonight into early Monday morning, followed by less cold conditions by midweek.

DISCUSSION

Issued at 245 AM CST Sun Feb 1 2026

A much quieter start to the day compared to the last two with a surface ridge shifting across Illinois. A mid-lake convergent axis from Saturday has persisted this morning owing to a modest land breeze off Lower Michigan and northern Indiana. An associated narrow corridor of stratus extending southward along the Illinois shore and across northwest Indiana may be able to squeeze out a few flurries, but observed cloud depths appear too shallow to support anything more.

A pair of well-defined mid-level waves over the eastern Dakotas this morning will track southeastward through tonight, with the southern wave becoming increasingly sheared over southern Illinois this afternoon and the northern wave weakening over Wisconsin this evening. Another wave currently over Saskatchewan will phase into the northern wave overnight. Meanwhile, a 110 knot upper-level jet will pass southwest of the area. Given sufficient mid-level moisture observed upstream but weak ascent from the lack of formidable forcing, expectations are for an axis of very light snow to drift across the CWA from west to east early this evening through sunrise Monday. Accumulations up to one half inch are possible areawide, though would not be surprised to see an area with little to no accumulation where (most likely the southwest CWA) the weak forcing is split by the jet to the south and wave to the north.

Mid-level moisture will quickly exit Monday morning, but lingering low-level moisture and diurnal processes may result in some flurries across the area midday.

A conglomeration of several waves loosely phasing across the central and southern Great Plains on Tuesday will induce an elongated surface trough across the lower half of the Mississippi River Valley. As the northernmost wave digs southeastward from the Dakotas to southern Illinois Monday night into Tuesday, a narrow frontogenesis/deformation axis pivoting on the north side of the wave has a <20% chance for accumulating snow to brush the far southern CWA. Have maintained a dry forecast as trends in ensemble guidance have been toward a drier and more southern solution with time.

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. Have included chance PoPs with little accumulation during this window.

Broader northwest flow will persist midweek through next weekend. Temps may moderate to above freezing by Thursday or 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. A return to colder conditions should then prevail next weekend.

Kluber

AVIATION /18Z TAFS THROUGH 00Z TUESDAY/

Issued at 1134 AM CST Sun Feb 1 2026

Forecast concerns include...

Period of light snow expected tonight. Mvfr cigs tonight into Monday morning.

Light snow currently over eastern IA and far western IL is expected to dissipate as it slowly moves southeast and remain southwest of the terminals. Some flurries are possible at RFD by late this afternoon. An additional area of snow across eastern MN will move southeast into the area this evening bringing a period of light snow to all the terminals. This snow is expected to be rather light and there remains uncertainty for how low the visibility may drop. Maintained tempo 2sm at RFD and 3sm at the rest of the tafs for now, but as trends emerge later this evening, these may need to be adjusted and its possible a 2-3 hour period of prevailing light snow may be needed. This snow is expected to move east of the terminals before daybreak Monday morning though flurries will be possible through midday.

Mvfr cigs are expected once the snow begins later this evening. Brief ifr cigs are also possible, depending on how widespread the snow becomes. Low mvfr cigs are likely to continue through mid morning Monday, scattering out from west to east, though only medium confidence for cig trends Monday.

South/southwest winds may periodically gust into the 15-20kt range this afternoon and then diminish this evening, turn southwesterly overnight and west/northwest Monday morning. cms

HYDROLOGY

Issued at 245 AM CST Sun Feb 1 2026

River gauges, reports from local officials, and reports from trained ice spotters continue to indicate a few ice jams across the area. Additional ice formation should slow with daytime temperatures mainly in the 20s to low 30s through the upcoming week. While no widespread flooding is expected, localized ice jams may still develop.

- NWS Chicago

LOT WATCHES/WARNINGS/ADVISORIES

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