textproduct: Chicago

KEY MESSAGES

- A wintry mix with snow and freezing drizzle overnight into early Friday morning. Locally hazardous travel may result.

- A sharp cold front will race through the region Friday afternoon. Snow showers, including squall-like behavior, may accompany the front.

- A period of nuisance lake effect snow will occur in northwestern Indiana Friday night through Saturday.

- A pattern shift will occur next week toward warmer, and potentially wetter, conditions.

UPDATE

Issued at 903 PM CST Thu Feb 5 2026

Precipitation is developing/spreading across northwest WI currently and this will move across the local area overnight into early Friday morning. The current forecast remains mainly on track though there continues to be minor shifts in the cam guidance, mainly wobbles to the northeast with the main area of precip. If a slightly northeast shift continues, this would likely allow the far western/southwest cwa to remain dry, while bringing the chance of freezing drizzle further east into the Chicago metro area. Some of the precipitation may also be partially convective, thus pockets of freezing rain will be possible, but perhaps not widespread. Opted to maintain the freezing drizzle mention (vs. adding freezing rain) but did bring the freezing drizzle across much of the area earlier then previously forecast. Confidence remains low for a winter weather advisory and opted to maintain the SPS at this time.

One other change was to increase the northwest winds much faster Friday morning. The precipitation duration will be short and as it ends Friday morning, northwest winds will rapidly increase with a period of gusts into the 35 mph range possible. cms

DISCUSSION

Issued at 257 PM CST Thu Feb 5 2026

A robust upper level jet-streak (140+ kt) currently overtopping the western CONUS ridge axis will carve out a reinforcing upper trough/low across the eastern Great Lakes into Saturday. As it does, an active northwesterly flow pattern will remain the dominant feature across our region. Of particular interest with this pattern is our next clipper-type impulse currently noted over the Prairie Providences of Canada. This feature will quickly dive southeast into the Arrowhead region of MN this evening, then right into our area by daybreak Friday morning. The main concern with this feature continues to be short, but ill-timed period of wintry precipitation early Friday morning.

The window for wintry precipitation from this weather system will remain rather short (~3-5 hours) late tonight through early Friday morning. Precipitation type will be problematic, particularly west-southwest of the Chicago metro area. In this region, low-level warm air advection is expected to drive the nose of a melting layer off the surface northeastward into northwestern and central IL. Also, the system track will favor more mid-level drying and potential lose of cloud ice west- southwest of the Chicago metro area. Accordingly, P-Types west- southwest of the metro will favor light freezing rain or drizzle and the potential for a light glazing of ice on untreated surfaces late tonight.

Across most of the northeastern IL into northwestern IN (including much of the Chicago metro area) the precipitation type late tonight into early Friday morning looks to be primarily snow. While the window for this snow will again only be 3 to 5 hours, there is concern that a "thump" of convective heavy snow may occur just before daybreak as mid-level lapse rates steepen (7C + per KM) considerably as strong dynamic forcing along the low-level baroclinic zone sets up within the exit region of the aforementioned upper level jet streak. If this materializes, we could envision a quick 1-2 inch snowfall across parts of the metro area in the 3 to 6 am timeframe.

With the increasing potential of this period of wintry precipitation into the early Friday morning commute we have opted to increase the messaging of this event with an SPS and through our afternoon forecast graphic push. At this time, we cannot rule out the need for a short fused Winter Weather Advisory, but will let the evening shift get another look.

The wintry precipitation will come to a quick end from northwest to southeast around and just after daybreak Friday morning. Surface temperatures will warm into 30s late in the morning, but attention then turns to the period of strong north- northwesterly winds (gusts 35 to 40 mph) expected in the afternoon following a cold frontal passage. Steepening low-level lapse rates may also support the development of some afternoon snow showers.

KJB

Friday night onward:

Falling temperatures behind the cold front (850mb values dropping toward -15C or so) and persistent north to northwesterly winds will support the development of persistent lake effect snow showers across northwestern Indiana Friday night through early Saturday. Considering the inner upper-level cyclonic shear axis will be well east of our area by then and a surface high will be building into the Great Lakes, inversion heights will struggle to climb beyond 5kft. Accordingly, the lake effect snow looks more like a nuisance than an impact, with perhaps a few inches of snow east of Gary by the time snow ends Saturday afternoon. Elsewhere, Saturday will be a brief chilly interlude with highs in the 20s. Thankfully, the arrival of the surface high should lead to somewhat light winds.

Looking toward next week, a powerful 200kt+ jet streak originating from the Kamchatka Peninsula of Russia will spur the development of aggregate troughing along the Pacific Coast of the US. As this occurs, a cut-off low pressure system will develop along the southwestern US/northwestern Mexico border. The net effect will be a substantial push of mid-level warm air advection across the central United States, allowing for the development of composite large-scale ridging through the Great Lakes. Confidence hence remains high in a period of above average temperatures next week.

Ensemble model guidance continues to exhibit a signal for the development of a synoptic-scale cyclone somewhere in the central US in the February 11-14 timeframe, though exactly how and where will likely depend on the evolution of the leading cut-off low pressure system and any ejecting shortwaves from the aggregate troughing along the Pacific Coast.

Borchardt

AVIATION /06Z TAFS THROUGH 12Z SATURDAY/

Issued at 1055 PM CST Thu Feb 5 2026

Key Messages for the 06Z TAFs:

- Period of wintry precipitation expected early Friday morning. Mainly snow expected for ORD/MDW/GYY, though can't rule out some sleet mixing in. More sleet may mix at DPA, with FZRA/PL more likely farther west toward RFD. IFR vis/cigs possible.

- Wind shift to strong NNW by mid-morning, with gusts 30-35 kt. Strongest push of winds may focus west of Chicago terminals. Winds only gradually diminish afternoon/night. - Scattered afternoon flurries and snow showers possible for Chicago terminals, with brief MVFR/IFR vis possible.

A strong upper level disturbance will dig southeast across the area into Friday morning, and is expected to produce a 3-5 hour period of wintry precipitation across northeast IL and northwest IN. Thermal profiles are warm enough farther west toward RFD that a mix of FZRA/PL is likely, while a slightly colder column farther east into the Chicago metro TAF sites should support primarily snow, though can't rule out some mixing with sleet. Precipitation may be somewhat showery, with varying intensity. Brief IFR/LIFR vis possible in periods of moderate snow, with accumulations up to 1-2" possible. Precipitation ends quickly toward mid-morning, as a sharp cold front pushes south across the area. Cooling of the column behind the front will likely support scattered convective snow showers during the afternoon, with brief MVFR/IFR vsby reductions, especially near the lake and for GYY. Otherwise, MVFR ceilings will gradually lift through the afternoon and early evening hours before scattering out. A few non-impactful flurries may squeeze out of this deck at times into the evening.

Surface winds are expected to turn north-northwest behind the cold front Friday morning, and become strong and gusty. Wind gusts in the 30-35 kt range are likely during the morning and early afternoon, with a few higher gusts possible especially at RFD as the axis of strongest winds appears to focus west of the Chicago metro. Winds will only gradually ease Friday afternoon/night.

Ratzer

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory from 8 AM Friday to 3 AM CST Saturday for the IL nearshore waters.

Gale Warning from 10 AM Friday to midnight CST Friday night for the IN nearshore waters.