textproduct: Chicago

KEY MESSAGES

- Areas of drizzle and fog this morning, with at least patchy dense fog for areas west of I-57 and I-355, and west of the Fox Valley in far northern Illinois.

- Very windy (gusts up to 50 mph or stronger) and much colder on Wednesday with snow showers and flurries possible for some.

- Blustery and cold weather will continue through the evening hours on Thanksgiving Day.

- The signal for widespread accumulating snow (and associated post-Thanksgiving travel impacts) this weekend continues to increase (~70% chance), starting late Friday night, and possibly lingering all the way into Sunday morning.

- Below to well below normal temperatures will persist into next week, along with the potential for additional rounds of wintry precipitation.

UPDATE

Issued at 701 AM CST Tue Nov 25 2025

A Dense Fog Advisory is in effect until 10 AM CST for areas primarily west of I-57 and I-355 (and west of the Fox Valley across far northern IL). Gradually deteriorating visibility has been noted at automated observation sites, including more spots with 1/4 to 1/2 mile visibility across interior northern Illinois and parts of central Illinois as of this writing. This is backed up by webcam imagery in these areas. It's a little unclear how widespread the dense fog will become in closer to the Chicago metro, though opted to err on the side of caution and include all of Will County (but not yet DuPage County) in the advisory. We'll continue to keep a close eye on trends for any possible expansion of the advisory.

Castro

DISCUSSION

Issued at 305 AM CST Tue Nov 25 2025

Our next wave of rain continues to shift northeastward into northern IL early this morning in association with the main approaching mid-level impulse. This area of rain will shift across the area through daybreak, then likely transition over to a period of drizzle and fog through most of the morning. The main concern that we will be monitoring is the threat of dense fog around and after daybreak this morning. Dense fog has recently developed across much of southern IA and into northern MO early this morning, and there is some concern that this area of dense fog will try to expand eastward into at least western portions of our area this morning. Confidence on the extent of any dense fog remains on the lower side, so we will continue to monitor observational trends this morning.

Regardless of the threat and extent of dense fog, very low clouds, fog and drizzle will make for a rather "soupy" morning for the area. While we should see conditions improve some through this afternoon, lower cloud cover is likely to persist into tonight. Temperatures today are thus expected to hold fairly steady, with readings only warming a few degrees into the low 50s.

Forecast attention then quickly turns to a northern stream impulse digging into the northern High Plains early this morning. This feature will strengthen considerably today into tonight as it digs over the Upper Midwest and ultimately becomes negatively tilted late tonight over the western Great Lakes. As this occurs, surface low pressure will rapidly consolidate and deepen to sub 995 mb near the Straits of Mackinac by early Wednesday morning. This will send an associated strong eastward surging cold front across our area this evening.

As has been advertised for the past several days, the main story with the passage of this front will be the turn towards very windy and much colder (winter-like) temperatures. This thinking has not changed, and with the increasing confidence for strong and frequent gusty winds of 50+ mph, we have opted to go ahead and hoist a wind advisory for the entire area from late tonight through Wednesday evening. There is even some concern that a period of near warning level criteria wind gusts (damaging winds of 58+ mph) could materialize during the period of strongest pressure rises (~6 mb/3hr) on the back side of the deepening surface low Wednesday morning. Currently, it appears the best chance for such gusts would be across southern WI and perhaps into portions of far northern IL (north of I-88). We will have to continue to monitor this potential.

Aside from the strong winds, we should also have a fast eastward moving line of showers accompanying the frontal passage this evening. Thereafter, wrap around moisture looks to result in snow showers and flurries developing into the area on Wednesday. It appears the best chance for this will be across far northern IL (north of I-80 and into southern WI), where some minor accumulations could materialize. Otherwise, expect very windy conditions through the day on Wednesday, with temperatures falling into the lower 30s and wind chills into the teens.

KJB

Wednesday Night through Monday:

The main forecast focus is on the increasingly likely (and possibly long duration as well) widespread accumulating snow event this weekend. While it's still too early to start mentioning specific amounts, there was much better agreement on the overnight guidance suites in potential for several inches of snow (ie. a plowable snowfall) for at least portions of the area. Our biggest impediment to higher confidence is that the prospective event is still 4+ days out, leaving plenty of time for sizable changes in how things evolve.

Prior to the (likely) snow onset late Friday night, it will be primarily dry but cold. This will particularly be the case on Thanksgiving Day due to still blustery west-northwest winds frequently gusting up to 35 mph into the early evening. With temps only topping out in the lower to locally mid 30s after morning lows in the 20s, wind chills will remain in the teens to around 20F through the afternoon. For any morning outdoor events (such as community "turkey trots"), wind chills will bottom out around 10F. Don't forget to dress for the cold weather.

Later Thursday night into Friday, ~1030 mb surface high pressure transiting the region will result in much lighter winds, though temps will be well below normal for the date (teens to low 20s lows and highs around 30F into the lower 30s).

Big picture wise, a strong short-wave trough will come ashore on the Pacific NW coast on Thursday-Thursday night. Then in response to amplifying ridging into the Gulf of Alaska, this short-wave will dig into the central and southern Rockies and result in lee surface cyclogenesis over eastern or southeast Colorado. The surface low will broaden and become elongated into Saturday across the lower and mid MS Valley. The details then diverge a bit Saturday evening into Sunday, serving to at least modulate the event magnitude (QPF, snow, impacts).

A broad area of strong warm and moist advection will develop over the central US, with this and upper jet diffluence resulting in an expansive area of precipitation. At this time, there is overall good agreement in the thermal profile and surface wet bulb temps being cold enough for snow. Some of the more notable question marks involve the strength of the synoptic system and potential for some deepening of the surface low into Sunday. The latter evolution would entail a longer duration of deformation type precip into Sunday, but also may entail some p-type issues in parts of the area depending on the track of the surface and 850 mb low. On the other hand, a weaker and more progressive area of primarily/solely warm advection type snow would result in an earlier end time to the accumulating snow (by Saturday evening).

The above is just to give a rough idea of the spectrum of outcomes, which range from a light to moderate event on some of the guidance members, to a bonafide snowstorm on a surprisingly large % of members. Can't ignore this despite it being far out, because the above normal column moisture (PWATs possibly over 0.6") and steep lapse rates above 500 mb do lend credence to periods of heavier snowfall rates. The major ensemble systems are basically in unanimous agreement in 1"+ snowfall in 24-hours already, but much more varied when looking at exceedance probabilities for higher snow amount thresholds, which is unsurprising at this range. Finally, a stronger, slower system would likely result in a couple day quiet but cold period in its wake, while the faster, weaker system may open the door for additional snow/wintry precip opportunities into early next week. Any nights that clear out under surface high pressure could be quite cold (single digits or colder in spots) if a good snowpack is established, which remains to be seen.

Castro

AVIATION /12Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 534 AM CST Tue Nov 25 2025

Key Messages:

- LIFR CIGs and VSBYs this morning, with periods of showers and drizzle.

- Strong cold frontal passage expected later this evening, with strong and gusty westerly winds (gusts 32 to 42 kt) developing in its wake and continuing on Wednesday.

- Snow showers and flurries likely (60%+ chance) after daybreak Wednesday. Some of the more vigorous snow showers could produce brief periods of IFR VSBY.

The last wave of rain is currently shifting across northern IL early this morning. While this is expected to shift east of the area after 14Z this morning, some lingering drizzle may continue for a few hours this morning. Of more concern, however, is the threat for deteriorating VSBYs after this area of rain ends this morning. There is currently a lot of sub 1/2 VSBYs across southern IA and far western IL trying to expand eastward. Current thinking is that conditions will drop at all of the terminals over the next few hours, with sub mile VSBYs likely. The big question mark is if sub 1/2 VSBYs will materialize into the Chicago area terminals. Currently, I think there is about 30-40 percent chance for such VSBYs at ORD and MDW after 14Z through late morning. We will continue to monitor observations and amend accordingly should conditions tank more than currently forecast. Improvement will be rather slow and gradual this afternoon, but we should see conditions lift into the MVFR category either late this afternoon or into this evening.

Another quick eastward moving line of showers is likely to accompany a strong cold frontal passage this evening. The winds will be the primary story in the wake of this front, with westerly winds quickly increasing and gusting in excess of 32 kt overnight tonight. Strong gusty westerly winds will continue through the day Wednesday, and peak gusts of 40-45 kts are expected during the daylight hours of Wednesday. Sporadic gusts into the 45-50 kt range can't be ruled out. A much colder airmass moving into the area will also support the possibility of snow showers and flurries on Wednesday. The more vigorous snow showers may, at least briefly, result in IFR VSBYs.

KJB

LOT WATCHES/WARNINGS/ADVISORIES

IL...Dense Fog Advisory until 10 AM CST this morning for ILZ003- ILZ004-ILZ005-ILZ008-ILZ010-ILZ011-ILZ012-ILZ019-ILZ020- ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ106-ILZ107-ILZ108.

Wind Advisory from 3 AM to 9 PM CST Wednesday for ILZ003- ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013- ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ103- ILZ104-ILZ105-ILZ106-ILZ107-ILZ108.

IN...Wind Advisory from 3 AM CST /4 AM EST/ to 9 PM CST /10 PM EST/ Wednesday for INZ001-INZ002-INZ010-INZ011-INZ019.

LM...Gale Warning from 3 AM Wednesday to 10 PM CST Thursday for the IL and IN nearshore waters.