textproduct: Chicago

KEY MESSAGES

- Another clipper system will move through the region centered on daybreak tomorrow with a threat for a wintry mix. 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.

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 /00Z TAFS THROUGH 06Z SATURDAY/

Issued at 555 PM CST Thu Feb 5 2026

Key Messages for the 00Z TAFs:

- Gradually lowering MVFR ceilings this evening, with MVFR likely to prevail through the remainder of the period.

- Period of wintry precipitation expected late tonight/early Friday morning. Mainly snow expected farther east into the Chicago area sites, while a mix of snow/sleet/freezing rain is more likely with westward extent (toward KRFD). Brief IFR/LIFR possible early Friday during precip along with some snow accums.

- West-southwest winds turn blustery north-northwest behind a strong cold front Friday morning. Gusts 30-35 kts likely during the day/early evening.

A weak surface trough will move east across the forecast area this evening, with the main impacts being a gradually lowering MVFR cloud deck and southwest winds diminishing and turning west- southwest.

Attention then turns quickly to a stout upper-level disturbance currently tracking quickly south-southeast out of southern Manitoba. This disturbance is forecast to track across the terminals Friday morning, resulting in the development of mix of wintry precipitation predawn with a burst of moderate snow through 8-9 am. Thermal profiles are warmer than we've seen in a while, setting up the potential for a mix of snow/sleet into the Chicago metro sites, and a mix of freeing rain/sleet snow farther west toward KRFD along the western periphery of the precipitation band. Current high-res model forecast soundings indicate Chicago terminals would see primarily snow, with visibility potentially dropping to less than a mile with accumulations of 1-2", but can't rule out some sleet at times. Slightly warmer temps aloft farther to the west would result in more sleet/freezing rain/freezing drizzle and an associated light glaze on untreated surfaces at RFD. Strong mid-level drying develops in the wake of the disturbance by mid-late morning which should quickly end the main precipitation threat, though there remains a low (10% chance) of some spotty freezing drizzle lingering for all sites during the morning.

A sharp cold front is then expected to push south across the terminals by mid-morning, turning winds north-northwest with increasing speeds/gusts. Sustained speeds near 20 kts and gusts frequently 30-35 kts are expected through the remainder of the day. A period of convective snow showers appear likely for a few hours in the mid-late afternoon, potentially with some brief MVFR/IFR visibilities. Otherwise, a few scattered flurries may linger into early evening from a gradually rising MVFR deck.

Ratzer

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory from 10 AM Friday to 3 AM CST Saturday for the IL nearshore waters.

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