textproduct: Chicago

KEY MESSAGES

- Blustery and cold weather will continue through Thanksgiving Day.

- Impactful snow is likely Saturday into Saturday night. It remains too early for highly specific snowfall amounts and locations, but there is a distinct potential for 6"+ amounts (and higher end travel impacts) in portions of the area.

- Well below normal temperatures will persist into or through next week, perhaps with additional chances for snow (Monday night).

DISCUSSION

Issued at 256 PM CST Wed Nov 26 2025

Through Thanksgiving Day:

A stout 993 mb surface low continues to traverse across the UP of MI this afternoon which has generated a very pronounced pressure gradient across much of the Great Lakes and Upper Midwest regions. As a result, westerly winds continue to regularly gust in the 45-50 mph range in northern IL and northwest IN. While a localized gust up to 60 mph still cannot be ruled out (mainly near the IL-WI line), it seems the higher concentration of these gusts should remain in WI. Therefore, we have opted to maintain the strongly worded Wind Advisory wind gusts up to 55 mph through 9 PM this evening. Outside of the wind, the associated upper trough has generated some isolated to widely scattered snow showers and flurries in WI with of few of these oozing into northern IL at times. Given the modest moisture noted in forecast soundings, expect these snow showers/flurries to be very hit and miss through early evening before the better moisture and trough pushes east into Lower MI. Regardless, little to no snow accumulation is expected.

Winds will gradually diminish through tonight as the surface low continues its eastward propagation. However, gusts in the 30-40 mph range still look to remain through the night and into Thursday morning. Otherwise, expect cloud cover to also diminish which will allow temperatures to dip into the lower to mid-20s overnight. The weather on Thanksgiving will again be on the chilly side with highs only expected to top out in the lower 30s. Though with continued breezy west-northwest winds gusting around 30-35 mph temperatures will feel more like the upper teens and lower 20s despite the partly cloudy skies.

Yack

Thursday Night through Wednesday:

A weak wave shifting SSE across Lake Michigan Thursday evening will sufficiently lift inversion heights to foster scattered lake effect snow showers across northern Porter County, with some flurries from stratus residing in the DGZ across northern Illinois and the remainder of northwest Indiana in the evening.

The main focus then turns to an increasing potential for a winter storm with several inches of accumulating snow across the region Friday night through Saturday. A strong trough currently approaching the WA/OR coast is progged to dig into the central Great Plains by early Saturday while phasing with a weak sub- tropical wave currently over the northern Baja of California. The combination of modest Pacific moisture from both systems as well as strong low-level moisture transport through the mid/lower Mississippi River Valley will yield a sizable shield of precipitation across the central CONUS. As the phased wave amplifies Friday night into Saturday morning, robust low-level WAA/isentropic ascent is expected to bring waves of accumulating snow across much of the forecast area. While accumulating snow is expected to continue over the area Saturday afternoon and night, solutions diverge with the ultimate track of the surface low as a result in differences in timing of the phasing and amplification. A somewhat bimodal solution exists in guidance:

1) The wave quickly amplifies and becomes slightly negatively tilted west of the area, bringing the surface low (and 925hPa) low well north into the forecast area (northern MO to Chicago track). This would support lower snow totals for part of the area as rain possibly mixes with the snow east of I-55 and along the immediate Illinois shore.

2) The wave strengthens gradually and tracks in a more ENE direction, producing a surface low that tracks from north of St. Louis to northern Indiana. This has become a more favored scenario is guidance over the past 24 hours and suggests precip will remain primarily all snow for much of the forecast area.

As can be expected, assessing snowfall amounts remains a challenge with this system owing to the magnitude of QPF (i.e. rate of amplification of the wave) and variability in snow ratios (exact track of the low). Focusing solely on QPF, ensemble systems overwhelmingly depict storm total values in the 0.5-0.75 inch range for nearly the entire CWA. Outlying members, specifically several within the EPS, indicate QPF over 1". Snow ratios continue to favor around the typical 10:1 values given the lack of substantial ascent within a shallower DGZ as well as robust low-level WAA. Putting all this together, it is feasible that warning criteria snowfall of 6"+ could be met for much of northern Illinois, particularly northwest of a Chicago to Mendota line where slightly colder thermo profiles support modestly higher snow ratios. However, if the southward trend in guidance persists, higher snow totals may focus south and include the entire Chicago metro. Given the potential impacts for travel over the holiday weekend, continue to monitor for forecast updates and, if necessary, consider adjusting travel plans.

The main snow shield should quickly exit to the east Sunday morning, leaving a period of strong CAA and flurries from shallow stratocumulus. Conditional on the presence of the fresh snowpack over the weekend, clearing skies and diminishing winds with an approaching surface ridge will promote a rather chilly Sunday night with lows potentially at or below zero across interior northern Illinois. Very cold conditions will persist through Tuesday as a reinforcing shot of colder air arrives on Monday. A mid-level wave crossing the Ohio River Valley late Monday afternoon and Monday night may brush southern portions of the forecast area with light snow. Sub-zero low will again be possible Monday night if the aforementioned system remains solidly south of the area.

Kluber

AVIATION /00Z TAFS THROUGH 06Z FRIDAY/

Issued at 559 PM CST Wed Nov 26 2025

- Strong WNW winds to continue through this evening (30-35 kt), remaining breezy through the period.

- Flurries may develop again Thursday evening (30% chance).

Winds will very gradually ease through this evening with prevailing gusts mainly in the 30-35 kt range, with any higher (40+ kt) gusts becoming more sporadic with each passing hour. While a brief bout of flurries can't be fully ruled out over the next few hours, earlier snow showers that resulted in visibility reductions have since moved out over Lake Michigan.

Winds will remain breezy overnight and through the day on Thanksgiving with gusts in the 25-30 kt range through the afternoon.

Ceilings will prevail mainly low-end VFR through the period. There is a low chance they dip back to high-end MVFR briefly overnight (~2500 ft), mainly outside of Chicago but confidence remains too low to include with this update. After thinning during the daytime hours (maybe even briefly scattering out?), the cloud layer is expected to deepen enough to support renewed flurry development after sunset tomorrow. Opted to introduce a PROB30 group for -SHSN (23-4Z) to account for this given the signal but do not expect any pavement accumulations or notable visibility reductions if they develop.

Petr

MARINE

Issued at 245 PM CST Wed Nov 26 2025

Key Marine Messages include:

- Storm Warning continues for the IL and IN nearshores through this evening. Gale Warning then continues tonight through Thursday evening.

A stout 993 mb surface low continues to traverse across the Upper Peninsula of MI which has generated a strong pressure gradient over Lake Michigan. These features have resulted in frequent 50 kt storm force winds over the lake this afternoon. While the storm force gusts will gradually subside this evening, 35-40 kt gales are expected to persist through Thursday afternoon and possibly into the evening hours. Regardless of wind magnitude, the west-northwest wind directions will continue to generate dangerous waves up to 10 to 14 ft with occasional waves up to 18 ft through Thursday especially on the eastern shores of the lake.

All that said, no changes have been made to the ongoing Storm Warning which remains in effect until 9 PM this evening and the Gale Warning that remains in effect until 10 PM Thursday evening.

Yack

LOT WATCHES/WARNINGS/ADVISORIES

IL...Wind Advisory until 9 PM CST this evening for ILZ003-ILZ004- ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ019- ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ103-ILZ104- ILZ105-ILZ106-ILZ107-ILZ108.

IN...Wind Advisory until 9 PM CST /10 PM EST/ this evening for INZ001-INZ002-INZ010-INZ011-INZ019.

LM...Storm Warning until 9 PM CST this evening for the IL and IN nearshore waters.

Gale Warning from 9 PM this evening to 10 PM CST Thursday for the IL and IN nearshore waters.