textproduct: Chicago

KEY MESSAGES

- A clipper system will move through the region today and bring chances (30 to 50%) for snow showers.

- Pockets of freezing mist and drizzle may develop after midnight tonight. In addition, relatively moist air moving over the cold ground may cause condensation and subsequent freezing on roadways. Confidence in either scenario is low (<25% chance for both).

- 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 evening. 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 315 AM CST Thu Feb 5 2026

There are a lot of subtleties to the forecast through the next 48 hours, so apologies for the length of the AFD.

Early morning GOES-19 water vapor imagery depicts an upper- level shortwave diving southward from southwestern Ontario toward western lake Superior and northeastern Minnesota. Ensemble model guidance remains in agreement that the shortwave will track generally just east of the Mississippi River today, reaching northern Illinois and northwestern Indiana by mid- morning. While the past few cycles of most model guidance has trended toward dry low-level air eroding all precipitation by the time the system reaches our area, the ECMWF has remained steadfast that showery activity tied to a plume of steep mid- level lapse rates in the core of the vorticity maxima will survive and sweep across our area. Accordingly, will cautiously advertise scattered showers in our forecast for much of the area, generally in a 2 to 4 hour window from late morning to early afternoon. Precipitation type should favor snow with the clipper, though would not be surprised to see a few reports of sleet due to the convective processes involved. While temperatures will still be below freezing as the showery activity races overhead, generally limited precipitation amounts (<0.05" liquid equivalent) should mitigate impacts on roadways where the precipitation does reach the ground. When also considering temperatures will rise toward freezing in most locations by early afternoon, the clipper today does not have the hallmarks of being too big of an issue.

Behind the wave this evening, low-level stratus may attempt to redevelop/lower in cloud base as low-level warm air advection gradually increases in advance of a secondary clipper system diving into the Great Lakes. While forecast soundings depict generally shallow depths to the stratus layer (around 2000ft deep), am growing increasingly concerned that pockets of freezing mist or drizzle may emerge by midnight, especially if cloud bases are able to lower below 1000 ft. The HRRR/RAP appear most aggressive in showing such a scenario, actually depicting a gradual decline in surface visibilities overnight, though never to values below 6SM.

Making matters more complicated is the threat for the ground, including parking lots and ground-based roadways, to "sweat" tonight. According to the University of Illinois WARM network, current 2-inch soil temperatures across the area are generally in the upper 20s. The frost depth at our office remains 13 inches. As surface dew points climb into the upper 20s tonight, the cold ground may start to condensate (much like a car windows will fog up when driving through cold/dry conditions). And, with temperatures remaining below freezing tonight, any ground sweat may be prone to freezing. Confidence in this process occurring is naturally pretty darn low especially since dew points may warm to, but not well above, ground/soil temperatures. Nevertheless, this sneaky phenomena has caught us off guard in past winter seasons.

The aforementioned second clipper will race across the area centered on daybreak tomorrow morning taking a similar track to the first. Compared to 24 hours ago, am noting a modest southwestward adjustment in the path of the system which would place more of our area in line to see precipitation. So, will gently increase PoPs to range from around 30% along a line from Mendota to Paxton to 70% near the Lake Michigan shoreline. Precipitation type with the second clipper looks problematic, as the combination of robust low-level warm air advection to warm the low-level temperature profile, mid-level drying to erode cloud ice, and surface temperatures remaining below freezing, may support snow transitioning to freezing rain. When also considering the system will be rooted to a plume of steep mid- level lapse rates, convective processes may lead to intermittent sleet, as well. So, parts of the area (highest PoPs near the Lake Michigan shoreline) may experience a true wintry mix tomorrow morning centered on the morning commute.

Put altogether, do think the Friday morning commute could be hazardous owing to a myriad of methods to make roads slippery, including preceding freezing mist/drizzle, overnight "ground" sweat, and an incoming wintry mix. If confidence in any of the three mechanisms for slippery travel increases, could easily envision the need for a Winter Weather Advisory across parts of the area. Will let the day shift take another look given the inherent low confidence. It does look like temperatures will warm above freezing by mid morning, so any roadway icing should melt by early afternoon.

If that's not enough, am noting HRRR/RAP guidance depicting quite a wind response behind the second clipper by mid Friday morning, as rapid pressure rises (6mb/3hr, 10mb/6 hr) push into the area. Forecast BUFKIT mixing profiles from either model would support north to northwesterly gusts pushing 40 mph at times, well above all other guidance that is more in line with gusts in the 20 to 30 mph range. Have seen HRRR/RAP guidance verify as too strong with winds 24 hours out beforehand, so hard to say if they are onto something. Regardless, if the winds do pan out, will have to watch for a legitimate snow squall set-up Friday evening as a sharp cold front dives southward through the Great Lakes. Such a threat would probably be highest near and especially downwind of Lake Michigan into northwestern Indiana, as building lake instability contributes to several hundred J/kg of instability along the front and temperatures tumble below freezing. Will introduce 20 to 30% PoPs across the Chicago metropolitan area and across northwestern Indiana for this potential for now, and let later shifts assess the threat further.

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 /12Z TAFS THROUGH 18Z FRIDAY/

Issued at 533 AM CST Thu Feb 5 2026

A pair of mid/upper-level waves will quickly track southeast over the western Great Lakes this morning. The first wave currently bringing SN at the surface in eastern Wisconsin should pass just northeast of the Chicago terminals through mid- morning as very dry low-level air erodes SN aloft. A second wave farther to the northwest with steeper lapse rates aloft will cross northeast Illinois mid to late morning. The associated heavier SN aloft should reach the surface in at least isolated pockets. Have therefore maintained TEMPO MVFR visibility 16-19Z, though cannot rule out IFR visibility briefly to 2SM or less. Otherwise, MVFR ceilings currently over northwest Illinois (e.g. RFD) will expand eastward over the Chicago terminals this morning, then lift and/or scatter for a period behind the precip this afternoon. SW winds around 10 knots at TAF issuance will gust up to around 20 knots this afternoon.

MVFR stratus should build back over the area this evening, then slowly lower through the remainder of the night. There is a low (<30%) chance that the stratus lowers into IFR levels and yields a deep enough layer to generate FZDZ overnight (06-10Z window) in response to low-level warm-air advection. After 10Z, another wave will track over and northeast of the area and bring a wintry mix of SNPL into mid-morning Friday. The SNPL may briefly change to FZDZ/DZ (temps rising to or above freezing) as the precip ends and a cold front crosses the area mid to late morning.

Kluber

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Gale Watch from Friday afternoon through Friday evening for the IN nearshore waters.