textproduct: Chicago

KEY MESSAGES

- Strong southwest winds become west and then northwest this morning with gusts to 35-40 mph through early afternoon.

- A period of wind-whipped snow may lead to hazardous travel during the commute this morning.

- More fast-moving clipper systems will likely result in some additional periods of accumulating snow in or near our area late this week into the weekend.

- Bitterly cold temperatures and potentially dangerously cold wind chills are expected this weekend.

DISCUSSION

Issued at 330 AM CST Wed Dec 10 2025

Through Thursday:

Quite the difference in model guidance compared to 24 hours ago for this morning's snow potential. The earlier concerns of a potentially robust snow squall tracking across the area have instead trended toward a broader area of snow with more muted snowfall rates over a slightly longer duration. This is associated with the trailing western portion of the elongated mid-level wave/vort, currently drifting southeast over southeast Minnesota toward the area. In addition to the snow, winds will remain rather gusty through the morning as we transition back to a cold advective regime, turning northwest to 35-40 mph behind the associated cold front. Regardless, the anticipated impacts for the Wednesday AM commute have remained largely the same with wind whipped snow and accumulations of up to 0.5-1" leading to hazardous winter driving conditions. Plan on extra travel time and take it slow on the roads this morning!

Hi-res guidance also continues to suggest a narrow lake effect band develops toward mid-morning into northeast Illinois that quickly pivots southeast into northwest Indiana and then east of the area by mid afternoon. Given the short duration over any given location, impacts may be more muted, but it could lead to locally higher totals near the lake of up to 1-1.5", highest in northwest Indiana near the lake.

Temperatures will steadily fall back below freezing in the wake of the front through the afternoon from northwest to southeast. Any lingering wet pavement will have the potential to become slick as well, particularly on untreated elevated surfaces which will cool more quickly than the ground. The breezy conditions may help dry things off somewhat, but recent rains may have also washed off the residual road treatments as well. Scattered snow showers and flurries could linger at times through the afternoon and particularly in the evening. This is associated with a subtle trailing low-amplitude mid-level wave moving overhead providing some weak lift within the stratus layer situated within part of the DGZ. Have held onto 20% chances through this time when an additional streaky dusting of snow will be possible. Temperatures continue to drop overnight into the upper single digits toward the WI/IL state and teens across the rest of the area. Minimum wind wind chills likely drop into the 0 to 10 degree range.

Our next clipper system will be approaching the area during the day on Thursday as temperatures warm into the 20s. While some light snow could begin prior to sunset over portions of northwest Illinois, the better potential exists for onset during the evening. More details on that are included in the long term discussion below.

Petr

Thursday Night through Tuesday:

The stubborn northwest flow pattern will persist over much the CONUS through the latter half of the week and into the upcoming weekend. With the energetic jet stream and associated baroclinic zone lining up directly over Illinois and Indiana, the barrage of clipper-type systems getting sent into the Midwest/Great Lakes will continue through at least this weekend with accompanying chances for additional snow accumulations to occur somewhere in or very near our forecast area.

The first of these late-week clippers is still slated to dive through the region late Thursday through early Friday, with Thursday night being the main time frame of concern for potential snow accumulations in our area. This clipper's surface low will track southeastward from South Dakota into the Lower Midwest with frontogenesis on its eastern flank expected to play a key role in inducing an elongated snow band within a northwest-southeast oriented low-/mid-level baroclinic zone. 00Z global deterministic and ensemble guidance generally depicted an overall southwestward shift in both the track of the clipper's surface low center and the associated QPF/snowfall footprint. It should be said, though, that there's still a non- trivial spread in the track of the surface low across all global ensemble suites, and this more southwesterly low track is not yet depicted in some of the higher-resolution guidance whose time ranges have only recently started to include the late Thursday/early Friday time frame. Thus, there's still room for additional shifts to occur in guidance over the next 24-36 hours.

If this more southwesterly track to the surface low were to verify, then that would favor any Winter Weather Advisory-worthy snow accumulations remaining confined to our southwestern counties, or even to areas farther southwest and primarily within the DVN and ILX CWAs. Some lesser snow totals would still be observed farther northeast, but the frontogenetically-driven nature of the snowfall suggests that there will likely be a fairly sharp snowfall gradient somewhere -- one that can't reasonably be depicted in our forecast grids at this range. Either way, with surface temperatures expected to fall into the low-mid 20s and teens Thursday night, even relatively "minor" snow accumulations could lead to a slick Friday morning commute for many.

Another shortwave trough embedded within the northwest flow aloft will track over the Upper Midwest on Friday. A majority of individual ensemble members favor the accumulating snow associated with this wave to largely remain to our north. However, there is still enough support overall for light snow getting into at least our northern counties to warrant maintaining some lower-end PoPs (20-40%) as output by the NBM for the Friday afternoon and evening time frame.

Then, a third shortwave trough is still expected to zip into the region on Saturday. The EPS, GEFS, and CMCE have all gradually jogged southward towards central Illinois and Indiana with this shortwave's associated QPF footprint over the past 24 hours, but there's still enough of an overlap with our CWA that the higher-end chance and lower-end likely PoPs from the NBM for Saturday still look fine for now. With much colder and drier air expected to be in place over the region at this time, any snow that does fall here will likely have a high snow-to-liquid ratio and, thus, a fluffy (and quite possibly even dust-like) character to it. One more shortwave trough may dive into the Great Lakes on Monday before the synoptic flow pattern finally starts to exhibit some changes, but the latest ensemble consensus favors its associated precipitation remaining north of our forecast area at this time.

The other weather concern for the long term portion of our forecast remains the likelihood of bitterly cold temperatures this weekend. Successive shots of cold air brought in by the aforementioned disturbances will likely culminate in single digit and sub-zero lows and possibly even single digit highs in many areas over the weekend. Confidence in our overnight/morning wind magnitudes still isn't particularly high at this point in time, but until a Canadian surface high settles over the region sometime Sunday into Monday, suspect that there's a good chance that northwesterly winds will remain high enough for minimum wind chills to reach (or at least get close to) our -20F threshold for Cold Weather advisories in some locations on at least one morning this coming weekend.

Ogorek

AVIATION /12Z TAFS THROUGH 18Z THURSDAY/

Issued at 615 AM CST Wed Dec 10 2025

Key Messages:

- Wind-whipped snow showers will produce sharply reduced visibilities this morning.

- A northwesterly wind shift will occur behind a cold front this morning with 30+ kt gusts likely after the frontal passage.

- MVFR/IFR ceilings will be observed this morning, and MVFR ceilings may then continue to be observed for several hours after the precipitation has ended this morning.

A deep low pressure system tracking through the Lower Peninsula of Michigan this morning will send a cold front through northern Illinois and northwest Indiana in the next few hours. Winds will shift northwesterly behind it, and 30+ kt gusts should start to be observed behind its passage as well. A period of wind-whipped snow will also be observed as the front moves through the area, which may result in temporary visibility reductions to 1SM or less and a quick dusting or coating of snow (primarily on colder surfaces). Prior to the arrival of the snow, a brief period of rain showers and/or drizzle will also be observed.

The snow should end by around midday, while the magnitude of the northwesterly wind gusts should steadily diminish thereafter through the afternoon. Another period of (more scattered/less widespread) light snow showers or flurries may then occur during the late afternoon and evening. Couldn't rule out some sub-VFR visibility reductions with this activity, but the larger concentration of steadier snow showers later today should remain west of the terminals.

Lastly, IFR/MVFR ceilings will occur this morning as the cold front and its associated precipitation move through the area. There is a chance that ceilings could lift/scatter to VFR by as early as this afternoon, but the more likely scenario is that MVFR conditions will persist through tonight before some scattering/clearing of the lower clouds starts to occur.

Ogorek

MARINE

Issued at 330 AM CST Wed Dec 10 2025

A Gale Warning remains in effect through this afternoon. Southwest gales become westerly early this morning then turn northwest after daybreak. The highest speeds, likely around 40kt with perhaps a few higher gusts, are expected when the winds shift northwesterly later this morning. Speeds will gradually diminish later this afternoon with gales expected to end by early evening.

Petr

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Gale Warning until 3 PM CST this afternoon for Winthrop Harbor IL to Gary IN.

Gale Warning until 6 PM CST this evening for Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.