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 /12Z TAFS THROUGH 18Z MONDAY/

Issued at 517 AM CST Sun Feb 1 2026

Outside of a band of MVFR stratus ebbing and flowing over GYY this morning, the TAF period will start with clear skies. Calm winds will become southwesterly after sunrise and increase to 10-12kt by mid-morning.

Attention then turns toward a clipper system moving southeastward toward the Lower Great Lakes. While upstream radar returns across southeastern Minnesota and northern Iowa look menacing, dry low-level air across northern Illinois should prove resilient through at least late afternoon with an outside chance (20 to 30%) that a few snowflakes survive to the ground at RFD by 21Z. Upper-level clouds will otherwise increase through the day from west to east.

Focus is instead on the area of snow crossing the Red River of the North at press time, which is tied to the 500mb shortwave axis of the clipper system. Since the shortwave will be shearing out as it approaches the region this evening, large- scale forcing will be rather weak if not nebulous. As a result, am not particularly confident that the area of snow will maintain complete intregity as it reaches and moves across the region this evening. Nevertheless, will maintain prevailing snow reaching RFD by 00Z and the Chicago terminals in the 03-04Z time window. Small snowflakes may prove effective at reducing visibility in spite of meager accumulation rates, so will maintain the inherited TEMPO groups, albeit shifted a hair later and with 3SM visibility. Snow should taper toward daybreak Monday. Total snow accumulations are not expected to exceed a few tenths of an inch at any given terminal.

Outside of snow, MVFR cigs should shift over the terminals this evening and continue through the early morning hours of Monday. Some attempts at clearing should take place from west to east after daybreak behind the cyclonic shear axis of the remnant shortwave. Finally, winds should remain southwesterly this evening and turn westerly toward the end of the TAF period.

Borchardt

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.