textproduct: Chicago

KEY MESSAGES

- Winter weather advisory is in effect through noon today for areas along and north of I-80 for additional light snow with wind gusts 30-35 mph potentially causing blowing snow.

- Accumulating snow to impact the Monday afternoon and evening commute and result in hazardous travel conditions.

- Well below normal temperatures will persist through next weekend with wind chills -5 to -15 possible Thursday and Friday mornings.

DISCUSSION

Issued at 255 AM CST Sun Nov 30 2025

Short term challenge is how to handle headlines. Periods of light snow will continue across northern IL and into northwest IN through late morning and as temperatures cool, the snow will become lighter/fluffy. Westerly winds will be gusting into the 30-35 mph range with some higher gusts possible this morning. These conditions will result in some travel impacts but no longer expecting warning level impacts and opted to replace the winter storm warning with a winter weather advisory until noon today for roughly areas along and north of I-80. Additional/new snowfall from this point until it ends this morning will likely be no more than one inch, with some areas possibly only seeing a dusting of new snow accumulation. There remains uncertainty for how long any lake effect snow may persist into Porter County and the advisory may need to be extended there, but for now opted to maintain the same expiration time of noon/18z. There will remain a chance of flurries this afternoon.

With the new snow pack and light winds tonight, low temps could really tank but there remains uncertainty for cloud cover with both slowly eroding lower clouds and then increasing high/mid clouds by daybreak Monday morning. Lows in the single digits across northwest IL to lower/mid teens elsewhere look ok for now, but changes may be needed based on cloud trends.

Attention then turns to the next accumulating snow that continues to speed up, now arriving during early/mid Monday afternoon. Ensemble support/agreement has steadily increased over the past 24-48 hours and blended pops have steadily climbed. Made additional upward changes to pops for Monday afternoon/evening with this snow now looking to start just before the Monday afternoon commute begins. With expected cloudy skies on Monday, high temps may only climb into the 20s allowing the snow to begin to stick when it begins falling. Qpf amounts in the 0.2 inch to maybe 0.25 inch range with snow ratios perhaps averaging 15:1 would yield 2-4 inches. While this is on the low side of an advisory, with it falling during rush hour, an advisory will need to be considered with later forecasts for this time period. The snow will be ending from west to east early Tuesday morning but with temperatures falling back into the teens, any untreated surfaces will likely still be slippery with at least some travel concerns for the Tuesday morning rush hour.

A cold front is expected to move across the region Wednesday with a chance of snow along/ahead of this cold front. Its possible the snow may develop right over the cwa and timing could also be for the Wednesday afternoon/evening commute. Still quite a bit of uncertainty for this time period. High pressure would then move across the area Thursday with the potential for some very cold temps both Thursday and Friday mornings, possibly subzero for at least parts of the area. Winds might still be in the 5-10 mph range both mornings with the lowest winds during the day Thursday, resulting in morning wind chills both mornings possibly in the -5 to -15 range.

Still several days away, but will need to continue to monitor another possible accumulating snow for Friday afternoon/evening as there is growing ensemble support for this time period. cms

AVIATION /12Z TAFS THROUGH 18Z MONDAY/

Issued at 546 AM CST Sun Nov 30 2025

Key Aviation Forecast Messages:

- Lingering light snow this morning, with intermittent IFR conditions. Period of slightly more intense light snow and solid IFR potential 12-16Z, with some minor accumulation potential.

- MVFR stratus lingers through this afternoon, but may persist overnight especially south/west of terminals.

- Strong W-WNW winds gusting near 30 kts this morning, gradually easing this afternoon.

Surface low pressure associated with our winter storm was over central lower MI early this morning, pulling away from the area to the northeast. A secondary cold front trails across far southern WI however, and will push southeast across the terminals this morning. This will be accompanied by a band of somewhat more intense snow for a few hour period roughly between 12-16Z, with associated IFR vis/cigs (potentially brief LIFR vis) and some additional minor accumulations of up to 1 inch. Light snow should then end late this morning though can't rule out a few stray flakes/flurries from the stratus deck with no vis impacts or accumulation into this afternoon. MVFR stratus will linger through the afternoon and should scatter out by evening, though may persist not too far tot the south and west of the terminals.

Surface high pressure builds across the area late tonight, with a period of light/variable winds after midnight turning light southwest Monday morning. Some guidance develops fog predawn within the surface ridge, though high/mid clouds quickly build back into the area early Monday morning, making for lower confidence in any fog development at this time. Mid clouds thicken Monday in advance of the next weather system which will bring snow back to the terminals by Monday afternoon, just beyond the end of the current 30 hour ORD/MDW forecasts.

Ratzer

LOT WATCHES/WARNINGS/ADVISORIES

IL...Winter Weather Advisory until noon CST today for ILZ003-ILZ004- ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ020- ILZ103-ILZ104-ILZ105-ILZ106-ILZ108.

IN...Winter Weather Advisory until noon CST today for INZ001-INZ002.

LM...Small Craft Advisory until 10 PM CST this evening for the IL nearshore waters.

Small Craft Advisory until 7 AM CST Monday for the IN nearshore waters.