textproduct: Chicago

KEY MESSAGES

- Winter Storm Warning now in effect for all but Ford, Iroquois, Newton, Jasper and Benton Counties, where a winter storm watch remains in effect.

- 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).

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 /12Z TAFS THROUGH 18Z SATURDAY/

Issued at 536 AM CST Fri Nov 28 2025

Widespread snow is expected to move into the terminals late tonight, with conditions likely deteriorating to LIFR/VLIFR in accumulating snow Saturday morning/midday.

Quiet VFR weather conditions will remain in place across the forecast area through this evening. Breezy west-northwest winds will persist this morning with a few sporadic gusts near 20 kt possible, though winds will generally be decreasing through the day as surface high pressure builds in from the west. Winds should become light/variable by evening and light southeast overnight.

A mid-level disturbance currently moving ashore across the Pacific Northwest is forecast to lead to surface low pressure development across the Plains later today/tonight. This low is then expected to track northeast into the western Great Lakes region through Saturday night. Widespread light snow is expected to develop in advance of this system tonight, then intensify across the area Saturday morning and persist through Saturday night before tapering off early Sunday. Confidence is somewhat low on exact start time tonight, as there will be some low-level dry air to overcome, but the expectation is that snow will develop near/after midnight and become moderate to heavy by mid-late Saturday morning. Current TAFs thus depict a deterioration in conditions with vsbys 1-2SM by daybreak and eventually less than 1SM by late morning/midday Saturday. LIFR/VLIFR conditions will most likely persist beyond the end of the current ORD/MDW 30 hour TAF period Saturday afternoon/evening. Southeast winds will increase into the 10-15 kt range Saturday morning, with some gusts 20-25 kts possible toward and beyond midday.

Ratzer

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 Watch from late tonight through late Saturday night for ILZ033-ILZ039.

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

Winter Storm Watch from late tonight through late Saturday night for INZ010-INZ011-INZ019.

LM...Small Craft Advisory until 9 AM CST this morning for the IL nearshore waters.

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