textproduct: Chicago

KEY MESSAGES

- Periods of moderate to heavy snow will continue into this evening producing hazardous travel conditions. The worst conditions are ongoing and will persist into this evening, but snowfall rates will ease sharply after 8 PM.

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

- Well below normal temperatures will persist through next week.

DISCUSSION

Issued at 219 PM CST Sat Nov 29 2025

Through Monday:

Large scale ascent is peaking across the region with our storm system in full swing at this hour. Persistent, broad UVVs on the order of 10-15 ubar/second through a 4-6 kft thick DGZ near and north of I-80 has really helped improve snowflake quality and resultant SLRs since noon, and this will continue through the rest of the day, supporting snowfall rates around one half to, intermittently, one inch per hour.

A notably more convective look to the satellite and radar has recently taken place across central Illinois where 500-600 mb lapse rates are steepening ahead of the northward-advancing dryslot. This has allowed for the development of some embedded lightning strikes where large scale forcing and the steepest lapse rates intersect. As a result, wouldn't be totally surprised to see a flash near our far south (southern Ford to Benton counties) during the 3pm-6pm timeframe, along with a period of briefly very heavy snowfall rates into the 1-2 inch/hour range in that same time window. Latest trends and guidance suggest the main potential area for these higher rates will set up in the vicinity of a Gibson City to Paxton line, but this will be a short window.

The system dryslot will impinge quickly on our locales south of the Kankakee River Valley through this evening. This will gradually result in the loss of cloud ice and will transition lingering precipitation to very poor-quality snow, if not even flipping things entirely to drizzle late this evening and into the early overnight. Temperatures will be slowly warming to at to just above freezing as this occurs, limiting the potential for any icing impacts. Some additional light snow will be possible as the low departs very early Sunday morning.

Farther to the north, it looks like we should hold onto just enough saturation colder than about -10 C that things should stay all snow north of about I-80. Here, snowfall rates will diminish through the evening, with just another 2-3 inches of snow expected overnight.

West to northwesterly winds will steadily increase overnight as the surface low pulls away, and some gusts could possibly push 40 mph south of I-80. With the warming temperatures, not sure this will be enough to worsen any blowing snow threat, so continued to leave this out of the gridded forecast but do continue a mention west of the Fox Valley Sunday.

Continue to see a signal for one last batch of snow Sunday morning in association with a trough axis that will push south out of Wisconsin after 5-6 AM. This feature looks to be pretty progressive, so will limit residence time, but this could end up squeezing another quick inch or two of snow near and north of about I-90 before precip shuts off by mid-late morning. Some modest lake effect could persist across parts of NE Porter county through mid afternoon, but the flow largely looks to shift westerly enough to push the main focus east of our region. Will continue to keep an eye on this, but at this time, no plans for headline extensions.

Carlaw

Monday Night through Saturday:

Focus will be on a quick hitting snow event for Monday afternoon and evening. This system is still developing off the Pacific NW and dig into the Great Basin and then to the central Rockies by early Monday. Model guidance depicts additional shortwave forcing emanating out of the Canadian prairies in a largely positive to neutrally tilted trough. The degree to which this northern energy strengthens will play a role to the degree of impacts from the snow in this event, particularly for areas north of I-80. The left exit region of an increasing upper jet will promote a decent area of lift, which will allow an area of snow to expand across most of the area Monday afternoon. Any strengthening frontogenetical circulation, albeit transient, could also translate to higher impacts away from the currently favored region for elevated snowfall totals which is along and southeast of I-55, where the low level mass response will be focused.

Probability matched mean QPF is consistent with the ensemble envelope of 0.1 to 0.2 inches of QPF, highest southeast, with less than 0.1" northwest of the Chicago area. This would translate to a light snowfall toward Rockford to 3" along and southeast of I-57. While forcing is modest, an increasing dendritic growth zone could promote a bit fluffier snow than this past weekend. There are certainly some details to be worked out here, but a quick hitting impactful snowfall seems on tap for the Monday afternoon and evening commute where many will be back at work following the holiday.

KMD

AVIATION /18Z TAFS THROUGH 00Z MONDAY/

Issued at 1144 AM CST Sat Nov 29 2025

18z TAF Forecast concerns:

-Moderate to occasionally heavy snow this afternoon into the early evening - we are entering the period of peak impacts.

-LIFR visibility with occasional VLIFR (temporary 1/4SM at times) in heavier bands

-Increasingly gusty southeast winds mid to late afternoon

Snowfall will hit its peak intensity this afternoon, thus expect prevailing LIFR conditions with visibilities in the 3/4SM to 1/2SM range in many locations. 1/4SM visibility will mix in from time to time as snowfall rates ramp up to near 1" per hour this afternoon. There is a little hole on radar well southwest of the terminals, but expect that to rapidly fill back in, and we will need to consider prevailing 1/2SM visibility for all the terminals. Winds have been slow to respond but will gusts into the lower 20s (or even mid 20s) later this afternoon and early evening.

There will be a secondary surge of snowfall, with some rain mixing in from southwest to northeast through the evening. We will hold snow at most of the terminals, maybe with the rain/drizzle mixing in at KGYY. Even as visibility may inch up mid to late evening, ceilings will fall as low pressure will move overhead.

Winds will quickly turn around to the WNW overnight into early Sunday. Expect another batch of snow showers tomorrow morning before turning to flurries and ending. Gusty WNW winds will continue (to 25 kt) through the day with MVFR ceilings returning.

KMD

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 until 10 PM CST Sunday for the IL nearshore waters.

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