textproduct: Chicago

KEY MESSAGES

- There is a chance (40%) for a very narrow band (or bands) of accumulating snow late tonight, currently favoring areas south of a Rockford to Chicago to Valparaiso line.

- Lake effect snow showers may meander near the Indiana and Illinois shores of Lake Michgian Tuesday into early Wednesday morning (30% chance).

- Temperatures may warm above freezing Thursday and more likely Friday then cool again heading into the weekend. - A pattern change toward warmer temperature (highs and lows both above freezing) may materialize by the middle of next week.

DISCUSSION

Issued at 315 PM CST Mon Feb 2 2026

Much of the area has been blanketed in low-level stratus all day paired with intermittent flurries thanks to the cloud layer being situated near/into the DGZ. As a result, temperatures have only warmed a few degrees today in the mid-upper 20s. However, some areas west of I-39 have managed to clear out this afternoon allowing temperatures to warm into the lower 30s in spots. It is possible further erosion of the edge of the cloud layer may occur prior to sunset. Expect the flurries to also gradually wane heading into the evening hours as the cloud layer continues to thin.

Looking ahead to the overnight hours, a clipper system currently pushing through the Dakotas into Minnesota is expected to move toward and across northern Illinois into Indiana late tonight into early Tuesday morning (~11 PM - 6 AM CST). The majority of hi-res guidance shows hints of this feature holding together into the area but only show streaky dustings of snow. Suspect they are struggling to resolve this smaller scale feature amidst limited moisture advection into the area. However, forecast vertical profiles within this potential band appear supportive of a brief window when sufficient saturation within the DGZ paired with steep lapse rates could result in a quick burst of snow and a axis of 0.5-1" of accumulations (maybe even locally higher) within a narrow band. Low to mid- level frontogenesis appears somewhat ephemeral and could be indicative of one or more very narrow bands occurring rather than one lone band, and confidence in where remains low overall. Based on the trajectory of snow upstream, it currently favors areas along a line from Sterling to Kankakee to Rensselaer. Have kept snow chances a bit more broad brushed than what will likely end up occurring for now.

As the clipper departs to the east Tuesday morning, northerly low-level flow sets up over the area. This will allow low-level convergence to set up over southern Lake Michigan which could set the stage for an extended period of (mainly light) lake effect snow showers into northwest Indiana (at times meandering into northeast Illinois) Tuesday through early Wednesday morning. Inversion heights are not especially high, but with sufficient lift within the DGZ could support accumulations up to 0.5-1" to locally higher. Dry conditions are expected across the rest of the area away from the lake. Temperatures Tuesday and Wednesday will remain cooler, with highs only in the 20s amidst weak northwesterly cold air advection.

Northwest flow will remain in place aloft late week with multiple waves expected to dive across the region which could lead to occasional periods of snow. Confidence in the timing and strength of these features remains on the lower side, but keeping an eye on Thursday morning, again Thursday night Another wave dives through Thursday. As confidence increases in the timing of these features, higher snow chances may become warranted than the current blended guidance.

Temperatures will gradually warm through the end of the work week with highs potentially in the mid 30s to around 40 by Friday, though there remain differences with respect to just how warm we end up. Stay tuned. This "warmth" will be rather short lived with a strong cold front expected to push through late Friday with high temperatures back into the 20s to around 30 over the weekend.

Petr

Next week:

Looking toward next week, ensemble model guidance exhibits a strengthening signal that the exceptionally persistent northwesterly upper-level flow pattern that has thus far defined winter across the central/eastern United States may temporarily break. As a result, ensemble mean temperatures trend notably upward by the middle of next week and beyond, with both high and lows above the freezing mark. Indeed, the CPC temperature outlooks for the middle of February favor the above average category across much of the central US.

Also have to point out a growing signal for a southwest-flow synoptic scale cyclone somewhere east of the Rocky Mountains in the February 11-14 timeframe, with both the GEFS/EPS already favoring our area being on the warm side. Should a cyclone actually develop and we end up on the warm side, could easily envision forecast focus trending toward hydrology concerns considering the frost depth of just deeper than 13 inches at our office isn't going to vanish anytime soon.

Borchardt

AVIATION /00Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 559 PM CST Mon Feb 2 2026

Forecast concerns for the terminals...

- Band(s) of snow showers tonight could result in a period of reduced visibility and some accumulation at the terminals.

- Lake effect MVFR ceilings to develop Tuesday afternoon.

- Lake effect snow showers will also develop Tuesday afternoon/evening mainly in northwest IN.

Lingering MVFR ceilings continue to slowly meander eastward across northeast IL and northwest IN this evening and should be exiting the Chicago area terminals by 02-03z. Once these MVFR clouds clear VFR conditions should largely prevail through the rest of the period.

Currently there is a cluster of snow showers in southern MN and northern IA associated with a shortwave trough that is expected to pivot into portions of northern IL and northwest IN tonight. Initially it looked as if the bulk of any snow showers would remain south of the terminals, but since the snow showers are further east and north than guidance suggested the concern is growing that snow may be seen at the terminals. That said, there is still a fair bit of dry air over northern IL and northwest IN that will need to overcome so confidence on snow occurring is still somewhat low hence the reason for maintaining PROB30s at the Chicago area sites. However, confidence in snow is a bit higher at RFD so have opted to prevail flurries starting at 04z with a TEMPO for the aforementioned snow showers through 08z. Where this snow does occur, expect a period of 2-4 mile visibilities and MVFR ceilings. Accumulations with this snow will generally be under 0.5 inches but with some instability aloft a narrow swath of 1-2 inch amounts is not out of the question. Confidence is just low on where these higher amounts may materialize.

This snow will taper by early Tuesday morning and allow VFR conditions to return. However, a band of lake effect snow is expected to develop Tuesday afternoon and meander over northwest IN. With lake effect parameters being more marginal it seems visibilities should remain in the 3-6 mile range and mainly stay near and east of GYY. Though, some MVFR lake effect clouds are expected to ooze westward into ORD and MDW and persist through Tuesday evening.

Otherwise, expect northwest winds tonight to become more northerly Tuesday with speeds remaining around 5-10 kts. Wind directions may become east of north at ORD and MDW for a period of time Tuesday afternoon before turning back northwest Tuesday evening.

Yack

LOT WATCHES/WARNINGS/ADVISORIES

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