textproduct: Chicago

KEY MESSAGES

- Untreated surfaces such as sidewalks, parking lots, and roadways across interior northwestern Illinois may be slick after patchy freezing drizzle early this morning.

- Another clipper system will move through the area tonight with a 20% chance for a quick coating of snow at any given location (most areas should stay dry).

- Lake effect snow showers may meander across the northeastern Illinois and northwestern Indiana shores of Lake Michgian Tuesday night into Wednesday morning (currently a 20% chance for a dusting of snow).

- Temperatures will make a run for the freezing mark toward the end of the week, marking the end of a prolonged stretch of daily highs below 32 degrees. (Could be close to tying 15th longest stretch below freezing at both Chicago and Rockford). - A pattern change toward warmer temperature (highs and lows both above freezing) may materialize by the middle of next week.

DISCUSSION

Issued at 238 AM CST Mon Feb 2 2026

Through Tonight:

The central axis of a sheared-out upper-level shortwave is passing over northern Illinois and northwestern Indiana at press time. While snow with the system largely underperformed (a consequence of nebulous forcing for ascent offset from a narrow DGZ), a ribbon of freezing drizzle and fine mist apparently tied to modest WAA within the low-level stratus layer ahead of a weak cold front has proved resliliant while moving across north-central Illinois early this morning. Observations of ceilings and visibilities, as well as areal webcams, depict the most persistent freezing drizzle along and north of Interstate 88 and especially toward the Wisconsin state line. Will go ahead and issue a Special Weather Statement for Winnebago, Ogle, Lee, DeKalb, Boone, McHenry, and Kane counties to highlight the threat for untreated surfaces (such as roadways, parking lots, and sidewalks) to become icy this morning. With radar returns gradually decreasing as the shear axis shifts east of our area, the intensity of the freezing drizzle/mist should weaken toward Lake Michigan. All precipitation should cease by daybreak.

The next forecast items of concern are cloud and temperature trends today. Recent nighttime microphysics imagery depicts quite an expansive bank of low-level stratus extending back toward the Minnesota and South/North Dakota borders. Positive mid-level height tendencies atop a broad surface high pressure system moving across the northern Great Lakes point toward lowering inversion heights today, which would typically suggest that stratus will eventually scatter out. Of course, the speed at which this process takes place during the cool season is often wrought with uncertainty, as low-level stratus decks have a way of overstaying their welcome. In spite of a few holes in stratus starting to emerge across central Minnesota, will go the pessimistic route and advertise mostly cloudy across our area today. When combined with modest cold air advection, will advertise a relatively muted influence of the diurnal cycle on temperatures today with highs in the mid to upper 20s (just 5 to 7 degrees warmer than where temperatures are now).

Tonight, The clipper system currently meandering along the Montana/Canadian border will slip southeastward and pass through the Lower Great Lakes. In the absence of meaningful low-level moisture advection ahead of the wave (and in fact, northerly surface flow will be transporting low-level dry air into the Lower Great Lakes), chances for widespread snow with the clipper locally look pretty slim (<20%). With that said, forecast soundings and omega profiles from an ensemble of short-term model guidance depict lift and relatively steep lapse rates centralized in the DGZ as the system passes through, raising concern for a sneaky threat for a narrow band or two of snow with localized accumulations of up to an inch or so. Like forecasting convection in the summertime, it's difficult to pinpoint exactly where any streaky snow elements may develop 24 hours out. So, will offer broad-brushed low (20%) PoPs across the entire area tonight keeping in mind most areas probably won't see a snowflake.

Tuesday through the upcoming weekend:

A surface high pressure system will build into the Great Lakes on Tuesday, helping clear any remaining clouds. Another push of modest cold air advection will hold afternoon high temperatures in the mid to upper 20s.

Tuesday night into Wednesday, somewhat disorganized aggregate upper-level troughing will redevelop across the Midwest/Great Lakes region anchored by several embedded shortwaves. One of the more dominant shortwaves appears poised to spur the development of a low pressure system somewhere in the lower Ohio River Valley, which in concert with the surface high pressure system centered in the Upper Great Lakes will set the stage for developing low- level convergence and lake effect snow across the southern shore of Lake Michigan. Depending on the eventual flow configuration that materializes between the surface high and low pressure systems as well as any augmentation by land breezes originating offshore of Lower Michigan, the lake effect snow could sneak into northeastern Illinois including into Chicago. With none of the upper-level shortwaves embedded in the cyclonic flow aloft currently expected to pass directly over Lake Michigan, inversion heights will remain pretty stunted and near or even below 5kft. As a result, the lake effect snow that develops will be more of a nuisance than anything else (certainly nowhere close to as intense as the past few lake effect snow events), with a few tenths of an inch to locally half an inch of snow expected generally within a 12 to 18 hour period. So, will continue to manually add low PoPs (20-25%) centered on the southwestern shore of Lake Michigan for the Tuesday night into Wednesday timeframe. Notwithstanding the lake effect snow showers, Wednesday looks pretty quiet otherwise with highs in the 20s.

Ensemble model guidance is in growing agreement that a clipper system will dive southward from central Canada and into the Great Lakes toward the end of the week. Aggressive warm air advection ahead of the clipper may allow for temperatures locally to reach the freezing mark Thursday or Friday, which would be the first time in 21 or 22 days (tying somewhere around the 15th longest stretch of temperatures below freezing at both Rockford or Chicago). Conceptually, would expect a quick hit of snow (or rain) with the clipper system, but exactly where will come down to the eventual track. A pool of seasonably cool air will anchor the clipper system, setting the stage for temperatures to fall by this weekend. Will note there is a signal for another clipper system sometime in the next Sunday/Monday timeframe in the general region, too.

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 /18Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 1202 PM CST Mon Feb 2 2026

Key Messages:

- MVFR ceilings will continue to be observed this afternoon before scattering out.

- There is roughly a 25-35% chance for a period of snow to be observed overnight tonight.

MVFR stratus continues to blanket the area early this afternoon. Some flurries have been leaking out of this cloud deck as well, and this may continue to be the case while the stratus remains in place. Between the back edge of the stratus approaching the terminals and the stratus thinning/eroding, a return to VFR conditions is likely this evening. However, lake-induced MVFR stratocumulus will make an inland surge sometime tomorrow morning, bringing a renewed period of MVFR ceilings to GYY, MDW, and possibly ORD tomorrow.

There also remains about a 25-35% chance for snow at the terminals overnight tonight as a mid/upper-level shortwave disturbance dives into the region. There is an increasing likelihood that there will be a narrow corridor somewhere in the area where the snow comes down at a fairly decent clip -- enough to reduce visibility lower than presently advertised in the going TAFs. However, the greatest likelihood for this appears to be south and southwest of the terminals, so only have visibility reductions down to MVFR in the going PROB30 groups at this time.

Ogorek

LOT WATCHES/WARNINGS/ADVISORIES

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