textproduct: Chicago

KEY MESSAGES

- Lake effect snow will return to parts of far northeastern Illinois and far northwest Indiana today, with the potential for several inches of new accumulations and travel impacts along the Lake Michigan shore.

- There may be a period of light snow accumulations Sunday night into Monday, followed by less cold conditions by midweek.

DISCUSSION

Issued at 331 AM CST Sat Jan 31 2026

Our reprieve from lake effect snow (LES) has been short-lived, as another prominent LES band on a low-level trough axis is working southwestward toward the Illinois and Indiana shores early this morning. This surface trough is expected to sharpen a low-level convergence axis along the Illinois shore and into far northwest Indiana this morning before drifting east and weakening this afternoon and early evening.

Unlike on Friday, the low-level flow should become more steady- state and allow and LES to remain more-or-less in the same vicinity for several hours. There remains only medium confidence on exactly where this band sets up, with the growing amount of lakeshore ice becoming a major wildcard. While some CAMs favor placing the main band solidly in Cook County, the amount of shore ice suggests that the band will anchor on or possibly slightly east of the shore.

Though inversion heights have lowered to around 5-6kft, much of the convective cloud depths remain in the DGZ. This should push SLR values at or above 20:1 within any focused band. So when all is said and done this morning into the afternoon, snowfall amounts of 2 to 4 inches appear likely under the band, with localized higher amounts of 6 inches. Whether those highest totals are realized over land (including downtown Chicago) or just offshore remains unclear. Much of the snow should fall through early afternoon, with snowfall rates over 1 inch per hour or higher under then main band this morning.

Headlines: The only minor change to the Cook and eastern Will County Winter Weather Advisories was to move up the start time to 5am for the earlier arrival of the initial lake band. As for northwest Indiana, opted to end the Winter Storm Warning in favor of an advisory given the lower totals and observed break from earlier heavy snow last evening.

Otherwise away from the LES, subtle ascent within the entrance of a weak mid-level speed max is allowing for an area of higher low-level moisture with the DGZ to produce light snow. Expectations are for periods of light snow showers or flurries to persist over much of the area through the morning.

Backing low-level flow and lowering inversion heights will end any remaining LES in northwest Indiana by late evening. A clipper like system will pass north of the area late Sunday into Monday morning, with an increasing chance of low-level WAA- induced light snow with accumulations under an inch Sunday night.

Overall northwest flow will persist through the upcoming week, though the coldest airmasses should stay well northeast of the area. Ensemble guidance continues to keep a stronger storm system to the south (over the Ohio and Tennessee Valleys) while another, albeit weaker, period of LES is possible into northwest Indiana and northeast Illinois Tuesday night into Wednesday morning.

Kluber

AVIATION /12Z TAFS THROUGH 18Z SUNDAY/

Issued at 539 AM CST Sat Jan 31 2026

A band of lake effect snow tied to a remnant inverted surface pressure trough and land breeze-enhanced convergence axis will continue to drift westward toward northeastern Illinois through the next few hours and eventually stall by mid morning. Exactly how far west and inland the lake effect snow penetrates and stalls remains an item of lower than average confidence, due to the weakening of the parent inverted trough/mesolow (currently located due west of the KIWX WSR-88D) and lowering inversion heights (to weaken the intensity of the convective processes). Indeed, have been noting a gradual decline in echo top heights from 10-11kft earlier this morning over central Lake Michgian to 7-8kft just offshore of northeastern Illinois at press time, as well as a decline in overall composite reflectivity values within the band.

At this point, an ensemble of CAM guidance remains insistent that the convergence axis will make it into and stall right along the shoreline, bringing lake effect snow showers close to or directly over MDW and GYY. So, will advertise prevailing MVFR and targeted IFR vsbys in TEMPO groups at both terminals, with the latter tied to maximized low-level convergence and omega profiles. Should the axis stall directly over MDW or GYY, a prolonged period (>6 hours) of reduced visibility below 3 miles may become realized, perhaps lasting into the early afternoon hours. With that said, a continued lowering of inversion heights should render snow more of a visibility issue than accumulation issue with time, especially by the afternoon. Meanwhile, at ORD, currently favor the convergence axis to remain just toward the east, allowing for a cautious removal of the inherited PROB30 group. Ultimately, today will be a day where AMDs will be needed as trends in the axis of lake effect snow evolve.

Outside the lake effect snow, the forecast is more or less straight forward today. Stratocumulus clouds located within the DGZ will support intermittent flurries and perhaps a few bonafide snow showers through daylight hours (RFD, DPA, ORD). Northwest winds will gradually turn westerly after sunset and settle on a southwesterly direction by the end of the TAF period. An approaching clipper system will warrant attention for an introduction of -SN in later TAF cycles.

Borchardt

HYDROLOGY

Issued at 230 PM CST Wed Jan 28 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...Winter Weather Advisory until 4 PM CST this afternoon for ILZ103-ILZ104-ILZ105-ILZ108.

IN...Winter Weather Advisory until 6 PM CST this evening for INZ001.

Winter Weather Advisory until noon CST today for INZ002.

LM...Small Craft Advisory until 2 PM CST this afternoon for the IL and IN nearshore waters.