textproduct: Chicago

KEY MESSAGES

- A Winter Storm Warning remains in effect for the entire area through early Sunday morning.

- Periods of moderate to heavy snow will spread across the area this morning and continue into this evening producing hazardous travel conditions. The highest snowfall rates and worst conditions are expected this afternoon into early this evening.

- Accumulating light snow (70-80% chance) late Monday afternoon into Monday night.

- Well below normal temperatures will persist through next week.

DISCUSSION

Issued at 226 AM CST Sat Nov 29 2025

Through Sunday Night:

No significant changes to the going forecast or reasoning.

Light snow continues to slowly spread into the area, saturating the low levels. Once it begins, light snow will continue into the morning hours and then increasing in intensity with periods of moderate to heavy snow expected areawide through the afternoon and into the early evening hours. Snowfall rates during this time may approach 1 inch per hour. Southeast winds will steadily increase through the morning hours with gusts into the 30 mph range possible this afternoon. This will likely lead to some blowing/drifting snow and expanded that mention across the entire cwa. As the surface low pressure moves across the northern part of the cwa this evening, warmer air will spread in allowing temps to warm to near or just above freezing along and southeast of I-55, allowing the snow to mix with or change to some light rain or drizzle. By this time however, remaining qpf amounts look rather light and while this may cut down on the snowfall amounts, it may not make much difference for the snow amounts. These warmer temps and possible mix should also end the blowing/drifting snow potential.

As for qpf/snowfall amounts and snow ratios, no changes. Areas southeast of a Pontiac to Valparaiso line will see the lowest amounts, likely in the 5-9 inch range with areas northwest of an Ottawa to Waukegan line seeing the highest amounts, with perhaps a few areas reaching one foot across northwest IL.

After the low moves northeast of the area tonight, winds will be shifting westerly, then northwesterly with cooler air spreading back into the area. There will likely still be light snow or snow showers falling overnight into Sunday morning and this snow will be drier with some blowing/drifting snow possible again, mainly across northwest IL. Though there may be a period of wind gusts into the 30-35 mph range Sunday morning and blowing snow may be possible wherever falling snow persists. It appears that light snow will be ending from northwest to southeast across the area Sunday morning with perhaps some flurries Sunday afternoon.

Lake effect snow may continue across Porter County Sunday afternoon into early Sunday evening. Low confidence for how long it may persist and for additional snowfall amounts and while some headline extension may be needed for Porter County, confidence is too low to make changes this morning. cms

Monday through Friday: Issued at 255 PM CST Fri Nov 28 2025

The primary forecast focus beyond this weekend's winter storm is the increasing potential for another round of accumulating snowfall during the Monday afternoon-Monday night. The multi- model consensus this morning continues to advertise a secondary shortwave dropping south through the Great Basin Sunday night and eventually ejecting across the Central Plains on Monday as a positively-tilted trough. This orientation would result in a fairly progressive system overall, but intensifying mid-level frontogenesis is forecast to result in an expanding region of generally light snow across parts of our forecast area. A significant north-south spread exists persists in the guidance and ensemble output today, but in general, the favored location for fgen-enhanced snowfall appears to be setting up somewhere across the southeastern two-thirds of the forecast area.

Main concern during this period is that snow would be falling into a cold airmass with surface temperatures in the upper teens to mid 20s which would easily result in slick/hazardous travel even with modest snowfall amounts. The other aspect that has our attention is some degree of near-upright/convective instability in recent model guidance above the main frontogenetic circulations which could end up locally-enhancing precip rates. At this time, liquid amounts are generally a quarter inch or less which would support perhaps 2-4 inches of snowfall given generally modest ascent through the DGZ and and cold surface temperatures. Too much uncertainty at this point to pinpoint the main threat area, but something we'll be keeping a close eye on over the coming days.

Increased cloud cover may end up tempering overnight lows/wind chills a bit more than the currently-advertised NBM grids, but cold conditions will nonetheless prevail next week. A reinforcing shot of cold air is generally forecast to arrive midweek as a roughly 1040 mb arctic high slides southward across the central CONUS, perhaps with an additional round of snow or at least flurries as the boundary layer saturates into the base of a very deep dendritic growth zone.

Carlaw

AVIATION /12Z TAFS THROUGH 18Z SUNDAY/

Issued at 538 AM CST Sat Nov 29 2025

Aviation forecast concerns for the 12Z TAFs:

- Deteriorating cig/vis conditions this morning as snow gradually intensifies across the terminals. Periods of LIFR VSBYs are expected, particularly this afternoon and early evening (localized VLIFR possible).

- Snowfall rates will average around 0.5"/hr but will peak around 1"/hr this afternoon/early evening.

- Southeast winds become gusty near 25 kts by afternoon. May be a period of variable directions later this evening as surface low pressure center tracks across northern IL. Winds become gusty from the west-northwest late tonight/Sunday.

Well-advertised winter storm is taking shape across the region early this morning, with surface low pressure along the KS/OK border at 11Z. A broad area of light snow has already spread into the forecast area predawn, and will gradually intensify this morning as the system continues to lift northeast into the region. Already seeing IFR vsbys at several of the TAF sites, and expect vsbys to continue to gradually deteriorate to LIFR through mid-late morning. A prolonged period of 1/2SM-3/4SM vsbys appear likely this afternoon into early this evening in periods of moderate snow, and some brief VLIFR can't be ruled out. Snow may mix with/change to drizzle later this evening, possibly as far north as KMDW/KORD, but most likely at KGYY. Snow intensity should taper off late this evening/overnight, with gradual improvement to MVFR conditions expected by Sunday morning though some light snow will likely persist.

As the pressure gradient tightens today ahead of the approaching surface low, southeast winds will gradually increase with gusts into the 25 kt range likely later this afternoon and early evening. Most model guidance has the center of the low tracking near/just north of KORD, which would support winds veering from southeast to southwest around/after midnight, then becoming west-northwest and becoming gusty again late tonight into Sunday. The exact track of the low and details of the winds late this evening are of somewhat low confidence prior to the shift to west-northwest. Gusty winds may produce some blowing and drifting of snow at times this afternoon/early evening as well as on Sunday.

Ratzer

LOT WATCHES/WARNINGS/ADVISORIES

IL...Winter Storm Warning until 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 until midnight CST tonight for ILZ033- ILZ039.

IN...Winter Storm Warning until 6 AM CST Sunday for INZ001-INZ002.

Winter Storm Warning until midnight CST /1 AM EST/ tonight for INZ010-INZ011-INZ019.

LM...Small Craft Advisory from 9 AM this morning to 10 PM CST Sunday for the IL nearshore waters.

Small Craft Advisory from 9 AM this morning to 7 AM CST Monday for the IN nearshore waters.