textproduct: Chicago

KEY MESSAGES

- Winter Storm Warning in effect for all of our Illinois and Indiana counties for late tonight into Saturday night.

- Impactful snow is expected late Friday night through Saturday night. There is a >90% chance for 6"+ amounts and higher end travel impacts along and north of I-80.

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

UPDATE

Issued at 1116 AM CST Fri Nov 28 2025

While no substantial forecast changes have been made at this time, there is enough 12Z model support to warrant upgrading the remainder of the Winter Storm Watch across the southeast CWA to a Winter Storm Warning. There continues to be some concern that a surging mid-level dry slot and warming low-level profile will quickly end most accumulating snowfall chances in the original watch area. However, given a relatively short period (9 hours or less) of higher snowfall rates, increasing southeast winds gusting to 30 mph, and associated impacts with holiday travel, it was determined that a Winter Storm Warning is warranted for this area.

Kluber

DISCUSSION

Issued at 259 AM CST Fri Nov 28 2025

Through Saturday Night...

Upgraded the winter storm watch to a winter storm warning for most of the area with increasing confidence for 6+ inches of snow. Maintained the winter storm watch for the far southeast cwa where snowfall amounts are expected to be less and there is some potential for a mix/change to light rain/drizzle late Saturday afternoon into Saturday evening.

Overall forecast reasoning remains on track with no significant changes to the forecast this morning. Light snow is expected to spread across northern IL late tonight/early Saturday morning with light snow falling across much of northern IL, north of I-80 by the predawn hours. The snow will then increase in intensity Saturday morning with the heaviest snow falling during the afternoon and then slowly tapering off in intensity from southwest to northeast Saturday evening. The snow will likely end completely early Sunday morning with perhaps some lingering flurries of snow showers later Sunday morning. The blended pops are in the high chance range and this seems a bit high, but did not make any changes. Lake effect snow showers may continue across far northwest IN, especially Porter County with additional snow accumulation possible and the winter storm warning may need to be extended for Porter County for these lake effect snow showers.

QPF amounts remain fairly steady from the models, generally ranging from 0.9 inches in the northwest and western cwa, to perhaps as low as 0.6 inches across the southeast cwa. Have generally maintained the snow ratios from the previous forecast, which for the bulk of the area may only be in the 11:1 or 10:1 range, perhaps a bit higher across the northwest cwa and a bit lower across the far southeast cwa. Combining these brings storm total amounts for much of the warning areas into the 6-10 inch range. Its possible areas where the watch remains in effect could reach 6 inches, but confidence is too low to upgrade those areas at this time. For areas northwest of an Ottawa to Aurora to Waukegan line, snow totals may be more in the 10 to possibly 12 inch range and a separate segment may eventually be needed but for now have just highlighted locally higher amounts for those areas. The track of the low will also need to be watched closely. Any north shift to the low track could have some large impacts on snow amounts.

Snowfall rates will likely be in the one inch range for several hours Saturday afternoon with some potential for a few hours of rates of 1-2 inches an hour, especially across northwest IL. cms

Sunday through Thursday: Issued at 301 PM CST Thu Nov 27 2025

A 1035-1040 hPa high building into the Great Plains impinging on the low over Lake Huron and Georgian Bay on Sunday will induce strong gradient winds and a modest 3-5mb/3hr pressure rise over much of the area. Some shallow blowing and drifting snow will likely persist for open areas conditional on a drier character of the expected snow pack. Will include patchy blowing snow in the forecast for now, with the greatest concerns on N/S-oriented roadways in open areas west of the Fox River Valley. Additionally, ongoing strong CAA with shallow stratus under a steadily lowering subsidence will support some lingering light snow showers or flurries well into the day Sunday. The lower inversion will also limit lake effect snow intensity near the lake in northwest Indiana, but additional minor accumulations are probable for northeast Porter County.

The inversion should lower enough to erode remaining stratus Sunday night as the surface ridge edges toward the area. As long as stratus does not persist well into the night, diminishing winds with a fresh snow pack 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 is now exhibiting decent phasing with a sub-tropical system over the Lower Mississippi River Valley, which supports increasing chances for light accumulating snow to affect at least the southern CWA during this time. Resultant higher cloud cover would ultimately tamper very cold conditions Monday night, but if there is any clearing, sub-zero lows will again be possible.

Deep troughing now anchored over eastern Canada will lead to colder conditions through the remainder of the week, with some energy from a Pacific NW trough bringing another period of potential snow to the western Great Lakes Wednesday into Thursday.

Kluber

AVIATION /18Z TAFS THROUGH 00Z SUNDAY/

Issued at 1126 AM CST Fri Nov 28 2025

- Snow overspreads the region late tonight/early Saturday morning.

- Cigs/vsbys will steadily deteriorate through the morning. Periodic dips to LIFR/VLIFR anticipated, particularly midday Saturday onward.

- Snowfall rates generally around one half inch per hour, but expected to peak near 1 inch/hour Saturday afternoon. Bulk of snow accumulations expected from about 1 pm to 8 pm.

Northwesterly winds will turn southerly this evening and eventually southeasterly tonight. Generally VFR conditions are expected today, with some patches of high-MVFR strato-cu developing.

Snow will overspread the terminals late tonight into early Saturday morning. Some uncertainty regarding the exact start time of light snow remains, but snow will gradually fill in and become steady through the morning hours with widespread IFR vsbys expected. Snowfall intensity is expected to peak Saturday afternoon, and this is the period most likely to result in LIFR/VLIFR conditions--at least on a temporary basis. The bulk of snowfall accumulations are expected during the roughly 12pm-8pm timeframe, with snowfall rates intermittently nearing 1 inch per hour during this period.

Southeasterly winds will also gradually increase through the day, with gusts increasing towards 25 kts during the afternoon.

Finally, just beyond the end of the current TAF periods: a mid- level dryslot is expected to quickly work its way northward Saturday evening. Temperatures will also begin to slowly warm, and this combination may result in snow mixing with or even changing to drizzle Saturday evening. This appears to be a lower potential at RFD, and locally greater potential at GYY and MDW.

Carlaw

LOT WATCHES/WARNINGS/ADVISORIES

IL...Winter Storm Warning from 3 AM Saturday to 6 AM CST Sunday for ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012- ILZ013-ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ103-ILZ104- ILZ105-ILZ106-ILZ107-ILZ108.

Winter Storm Warning from 3 AM Saturday to midnight CST Saturday night for ILZ033-ILZ039.

IN...Winter Storm Warning from 3 AM Saturday to 6 AM CST Sunday for INZ001-INZ002.

Winter Storm Warning from 3 AM CST /4 AM EST/ Saturday to midnight CST /1 AM EST/ Saturday night for INZ010-INZ011- INZ019.

LM...Small Craft Advisory until 3 PM CST this afternoon for the IN nearshore waters.