textproduct: Chicago

KEY MESSAGES

- Light rain or drizzle expected tonight into early Tuesday, along with the possibility for a period of locally dense fog.

- Very windy (gusts up to 45 mph or stronger) and much colder on Wednesday with light snow showers and flurries possible for some, and then continued blustery and cold conditions on Thanksgiving Day.

- There is a growing signal for accumulating snow and associated travel impacts in the region Saturday and into Sunday.

UPDATE

Issued at 812 PM CST Mon Nov 24 2025

Bumped up pops for this evening's initial round of light rain/showers, though going forecast otherwise appears to have trends well in hand. Will have to watch visibility trends overnight however, with areas of fog likely to form especially west/northwest of Chicago.

Regional radar mosaic currently depicts an area of light rain especially near and east of the I-55 corridor at mid-evening. This appears to be occurring in associating with a subtle mid- level wave lifting northeast ahead of the main short wave trough back toward the KS/MO border. This initial area of better coverage rain/showers should continue to lift northeast across the eastern parts of the cwa over the next few hours with a bit of a lull likely by late evening, though spotty light rain/drizzle should persist throughout the evening. High-res guidance is then in pretty good agreement in bringing another push of rain into the area after midnight, which also looks to favor the southeastern 1/2 to 2/3 of the forecast area. This second batch of rain should taper off to drizzle toward/just after sunrise Tuesday morning with the passage of the main mid- level trough axis.

Extensive low stratus has already developed into the mid- Mississippi Valley this evening, and will continue to spread across the forecast area over the next few hours. Also noting 1-3SM visibilities in fog developing upstream across western IL, and this will likely continue to develop into the overnight hours where rain persists. Plenty of guidance support exists for some denser fog to develop after midnight, especially across our west/northwest cwa where rain/shower coverage looks to be lower. Already seeing a few <1/2SM obs into southwest WI, and we'll have to keep an eye on this later tonight into Tuesday morning. Would not be surprised to eventually need a Dense Fog Advisory for at least west/northwest parts of the forecast area toward morning. Fog could linger for a decent part of Tuesday morning prior to the surface reflection of the upper trough moving off to the east.

Ratzer

DISCUSSION

Issued at 225 PM CST Mon Nov 24 2025

Through Wednesday:

On early afternoon water vapor imagery, a couple of separate impulses can be seen spinning over the central Plains each tied to a broader upper trough. A feed of Gulf moisture extends all the way to the upper Midwest in the system's "warm sector" and is responsible for the overcast skies hanging overhead today. To our west and southwest, light rain, fog, and ceilings below 1,000 ft have been lingering nearer to the centers of circulation. Such conditions will propagate into our area tonight into tomorrow as low pressure approaches from the southwest. Just as of around 1:30 PM, a few light radar returns are showing what appears to be scattered virga showers, or sprinkles at the most. Some patchy drizzle may start to fill in from the west late this afternoon. The plume of deeper moisture will lift into our area after 00Z allowing for a higher coverage of light rain and drizzle. This will continue through the night as a warm, moist upglide regime resides overhead. While we may see largely drizzle through the night, there should be enough moisture and forcing through the column to support true light rain showers from time to time. The more appreciable light rain potential should wrap up before mid-morning, and some drizzle may linger through the rest of the morning.

We'll find ourselves in a favorable location relative to the low track for low stratus and fog tonight and into tomorrow. In fact, we've been seeing periodic 3 mile visibilities in our west and southwest most of the day, and there's no reason that shouldn't maintain itself before conditions start dropping further this evening. There is good agreement among guidance in fog thickening across our west and northwest this evening and expanding around the CWA through the night. Probs for dense fog build after sunrise when we'll see a bump in dewpoints and are highest west of the city between the I-80 corridor and the WI state line. There is a signal from a number of camps for visibilities around Chicago to stay up near a couple of miles while the thicker stuff remains outside of the city. However, there is certainly a potential for dense fog to spread into and around the city tomorrow morning. The nature of any precipitation falling will also play a role in visibility impacts. Plan on a soupy, slow-moving morning commute tomorrow. Gradual improvements should take place after mid-morning, but the whole day looks pretty gloomy with the low ceilings continuing to hang overhead.

A digging upper wave will traverse the upper Midwest tomorrow afternoon into Wednesday. The surface response will be a deepening center of low pressure across northern WI and fast- moving cold front which is progged to move across our CWA tomorrow evening. Modest dynamic forcing ahead of the front could stir up a few light pre-frontal showers as early as dusk in our west, although precip chances are much higher along the front during the evening. It should be a rather brief stint of rain for any given area (maybe only a couple of hours). Being largely katafrontal in nature, profiles dry out very quickly behind the front. However, enough BL moisture may remain in place to provide some lingering flurries or very light snow showers amid the strong shear and cold advection tomorrow night through Wednesday, especially north of I-80. No accumulations are expected out of any this snow.

The bigger story regarding this front will be the strong winds and much cooler air following it. The cold advection will keep the boundary layer well mixed Tuesday night as a low level jet builds off the deck featuring as much as 45 kt of flow at 925mb and 50 kt beneath 850mb. Accordingly, we should be looking at westerly gusts in excess of 40-45 mph for much of Wednesday. The period of strongest winds appears to be between early morning and mid-afternoon before the LLJ starts to ease, but expect windy conditions to last into the evening. You might want to hang onto your steering wheel a little tighter on Wednesday, especially when traveling on open north-south roads. No decision just yet to issue a Wind Advisory for Wednesday, but we do appear to be heading in that direction.

These strong winds will advect a cold airmass into the region from the northwest and usher in a stretch of much cooler weather for the latter half of this week. 850mb temps are progged to drop about 15C between Tuesday and Wednesday evenings (that's 27F!). After surface temperatures fall into the lower and middle 30s in the wake of the front Tuesday night, the cold advection should balance with diurnal heating and daytime temperatures on Wednesday are expected to barely depart from morning lows. It's possible that we even cool a degree or two during the day.

Doom

Wednesday Night Through Monday:

Blustery conditions will continue Wednesday night through Thanksgiving. Temperatures in the 20s with the potential for single digit wind chills are possible through sunrise, where daytime warming will only approach the freezing mark with wind chills in the 20s. Winds will begin out of the west and turn to the northwest through Thursday morning. With favorable fetch and warm lake water temperatures supporting some lake induced CAPE, lake effect snow is possible through Thursday evening. However, it will likely be limited to just the far northeastern portion of Porter County, Indiana. Otherwise winds will slowly diminish Thursday evening. Weak surface high pressure will provide quiet, albeit cold, conditions on Friday.

Models have been somewhat consistent in developing a shortwave trough over southwestern Saskatchewan and eastern Montana early Friday morning and have it approach the western Great Lakes Saturday morning. As an inverted surface trough grows over the southern Plains, warm air advection should overspread much of Illinois and Indiana with much colder temperatures aloft. Ensemble probabilities are keeping fairly consistent signal for some amount of accumulating snow. However, models are still disagreeing on the exact track of that trough and how far south the colder temperatures will reach. GEFS models are suggesting a much warmer solution that allows for some snow (with minimal accums) on Saturday, before lifting and allowing for warmer temperatures through the column to transition to (potentially) all rain on Sunday. The EPS is far colder, allowing for traditional warm advection snowfall before a new surface low develops and allows for a cold conveyor belt of air to provide for a healthier chance for additional snowfall. For now, there was no need to change the PoPs the NBM provided. While it does allow for "likely" snow on Saturday, how this all transpires comes with a lot uncertainty and low confidence. That being said, considering how many people will use this weekend to travel following the holiday, it could provide a great deal of impact depending on which solution plays out.

There is a lot of uncertainty beyond Sunday. The EPS keeps things cold, while the GEFS warms afternoon temps. Both are suggesting high pressure could grow behind the system. So it is possible that PoPs are too high and drier conditions could in store for early next week.

DK

AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 1050 PM CST Mon Nov 24 2025

Forecast concerns include...

Lifr/vlifr cigs/vis with fog/drizzle overnight/Tuesday morning. Scattered showers through mid morning Tuesday. Ifr cigs Tuesday afternoon, mvfr cigs Tuesday night. Very strong/gusty southwest winds late Tuesday night/Wednesday.

A period of showers is expected overnight through mid morning Tuesday. Outside of these showers, areas of drizzle are expected, possibly lasting through midday Tuesday. There will be another chance of showers Tuesday evening ahead of a strong cold front. Toward the end of the new 30 hour ORD/MDW forecast, near daybreak Wednesday morning, there is an increasing chance of snow showers. Opted not to include these as they may be arriving around 12z, but trends will need to be monitored for later forecasts.

Ifr cigs have been as far east as DPA/06C this evening, but continue to remain west of ORD/MDW. Guidance trends continue to support low mvfr cigs developing in the next few hours for the Chicago terminals and quickly lowering into ifr and then into lifr and possibly vlifr for a time around/after daybreak. Further west including RFD/DPA, lifr/vlifr cigs/vis look on track. These lowest conditions will occur as a broad weak area of low pressure moves across the area. As this passes, visibilities should steadily improve with cigs lifting through ifr by early afternoon and likely into low mvfr during the afternoon with mvfr cigs continuing Tuesday evening into early Wednesday morning.

Light southeast winds are expected to become light and variable overnight and then shift light westerly by mid/late morning as the low shifts east. Winds will turn back southwest late Tuesday afternoon into Tuesday evening with speeds/gusts slowly increasing. Once the cold front moves through, west/southwest winds will quickly increase with gusts into the lower/mid 30kt range. Higher gusts, possibly to 40kts will be possible around and after daybreak Wednesday morning. cms

MARINE

Issued at 337 AM CST Mon Nov 24 2025

A powerful cold front trailing from deepening low pressure across the Northern Great Lakes will sweep across the lake Tuesday night. In the wake of the frontal passage, westerly winds will quickly increase, likely to gale force. The strongest winds, with gales possibly as high as 45 kt at times, look to occur during the day on Wednesday, with lower end gales then possibly persisting through Thanksgiving Day. A Gale Watch has been issued for all the waters of southern Lake Michigan, and is in effect from the pre-dawn hours of Wednesday through early Thursday evening.

Castro

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Gale Watch from late Tuesday night through Thursday afternoon for the IL and IN nearshore waters.