textproduct: Chicago

KEY MESSAGES

- Very low chance (<20%) for freezing drizzle north of I-88 late tonight into early Tuesday morning.

- A period of blustery winds and rain followed by snow showers is likely Tuesday night into Wednesday.

- After a brief warm-up Tuesday through early Wednesday, temperatures will turn sharply colder during the latter half of the week and into the weekend.

DISCUSSION

Issued at 353 AM CST Mon Dec 8 2025

Through Tuesday:

While lingering lake effect clouds have slowed cooling over portions of the metro and areas north of I-88, it will be a chilly start to the work week with temperatures early this morning in the single digits outside of the Chicago metro, teens in the suburbs, and upper teens to mid 20s in Chicago (warmest along the lake front).

A weak mid-level disturbance currently moving through Iowa will continue its eastward progress into Illinois this morning. While this feature has been producing some (mainly light) snow over central Iowa it will be encountering increasingly dry low to mid-level air amidst an expansive surface high. Nevertheless, the lighter echoes out ahead of the main band could still lead to isolated seeder-feeder generated flurries near and west of I-39 early this morning (~20% chance). Admittedly guidance has not been handling this feature all that well and it has remained rather persistent. While the dry conditions are still expected today, a slower erosion of the lower-level clouds here locally could perhaps support an additional brief bout of flurries in the afternoon.

As the center of the surface high shifts to the east through the day winds will return to a southerly direction. The warm advective influence will still be less pronounced initially, with the residual snow pack and mostly cloudy skies holding high temperatures in the low to mid 20s.

The next clipper system will approach the region tonight and move across Wisconsin into early Tuesday morning. This will help further increase the low level warm and moist advection out ahead of it here locally. Any precipitation associated with this system looks to remain mainly north of the local area, though some light wintry precipitation/flurries could graze far northern/northeast Illinois overnight into early Tuesday morning. The main concern during this time is whether freezing drizzle could develop instead of flurries. However, there remains notable variability among guidance as to whether we saturate sufficiently this far south for precipitation to occur. This will be monitored closely for possible addition to the official forecast if confidence increases as temperatures will still be below freezing during this timeframe and breezy winds would be supportive of more efficient ice accretion. Stay tuned.

Temperatures then warm above freezing by late morning/early afternoon with the possibility for lingering low clouds and patchy fog/mist making for a dreary day overall. Precipitation with yet another (likely stronger) system looks to mainly hold off until after sunset Tuesday. More details on that are included in the discussion below.

Petr

Tuesday night through Sunday:

The stubborn northwest flow pattern will persist over the western 2/3rds of the CONUS through this week and into the upcoming weekend. The energetic jet stream in place over the country will thus continue to send a barrage of clipper-type systems into the Midwest over the next several days, resulting in regular opportunities for (mostly wintry) precipitation and mostly below normal temperatures during this time frame.

What will likely be the strongest of this series of systems will pass through the region Tuesday night into Wednesday. Ensemble guidance is in relatively good agreement on a sub-990 mb surface low swinging across central or southern Wisconsin, though a minority of individual ensemble members have this surface low taking a track that brings it just south of the Illinois-Wisconsin state line. Robust warm air advection ahead of this deepening system will have pushed temperatures above the freezing mark during the daytime on Tuesday, and southwesterly surface winds strengthening further after sunset will keep temperatures propped up in the mid 30s to possibly even the low 40s through the night as the system's precipitation spreads into the area. Thus, while snowflakes could still be seen in some of our northern locales, the majority of precipitation that we'll see Tuesday night should come in the form of a cold rain.

Just how strong winds will get Tuesday night is still something that will need to be ironed out over the next couple of forecast cycles. Some guidance favors gusts exceeding 40 mph during this time frame when low-level pressure gradients will be most compressed, while other guidance is much more reserved, believing that precipitation and the deep snowpack in place over much of the area will stunt mixing into the stronger flow aloft. The precise strength and track of the surface low will also play a role in the magnitude of the winds that we'll see Tuesday night. For now, the NBM-delivered peak 25-30 kt gusts appear to be a good compromise between everything, but modifications to these gusts may need to be made as the event draws closer.

As the low pressure system makes it east of our longitude, cooler temperatures will work their way into the area on Wednesday behind a cold front. Precipitation on the backside of the low will thus be expected to change over to snow, though just how widespread the snow will be is another point of uncertainty with our forecast that is tied to the precise strength and track of the surface low, among other things. Regardless, any locations where gusty snow showers materialize will see sharply reduced visibilities and will have a chance to pick up a coating of snow if diminishing column moisture doesn't end up being too big of a negating factor.

Between Thursday and Sunday, 2-3 additional upper-level disturbances will ride the northwesterly flow train into the region. Each disturbance will come with a chance of producing additional snow accumulations here or somewhere nearby. However, there still isn't much consistency in ensemble guidance in the exact tracks, timing, and strength of each of these disturbances, which leads to continued low confidence in the finer-scale details of our precipitation forecast for the end of this week and this upcoming weekend.

Confidence is much higher that temperatures will turn sharply colder for the latter half of the week and into the weekend. The ensemble signal for single digit lows remains quite strong for this late week/weekend time frame, and there is a good amount of support for a sizable chunk of our forecast area seeing sub-zero low temperatures too. A period of blustery northwesterly winds behind an arctic cold front appears probable as well, which may allow wind chills to make a run at -20F at some point this coming weekend.

Ogorek

AVIATION /12Z TAFS THROUGH 18Z TUESDAY/

Issued at 614 AM CST Mon Dec 8 2025

Key Messages:

- MVFR ceilings are likely tonight, with some potential for IFR ceilings as well.

- There is about a 15-20% chance for freezing drizzle and/or a brief snow shower late tonight.

- Gusty southwesterly winds are expected tonight into tomorrow.

Early this morning, a stratus deck with 3000-3500 ft bases is sitting over RFD, DPA, ORD, and MDW. A few of these sites may barely meet MVFR criteria this morning before the stratus erodes and/or is pushed northward, leading to prevailing VFR conditions for this afternoon.

Tonight, a low pressure system will track eastward across northern Minnesota and Lake Superior, causing winds to turn southwesterly and become breezy here with gusts in excess of 20 kts. The bulk of this system's precipitation should remain north of the Illinois-Wisconsin state line. However, there is still about a 15-20% chance that a few snow showers or flurries make it far enough south to be observed at one or more of our TAF sites overnight. Furthermore, a few models suggest that the stratus deck could grow deep enough for freezing drizzle to be a possibility late tonight as well. Confidence in precipitation actually occurring was too low to warrant a formal mention of such a possibility in the TAFs at this time, though.

MVFR stratus is also expected to spread into the area after sunset. IFR ceilings could be observed as well, but like the potential precipitation, confidence in IFR ceilings occurring at any one TAF site through the end of the current 24-30 hour TAF period was fairly low at TAF issuance time.

Ogorek

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory from 9 PM this evening to noon CST Tuesday for Winthrop Harbor IL to Gary IN.

Small Craft Advisory from 9 PM this evening to 3 PM CST Tuesday for Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.