textproduct: Chicago

KEY MESSAGES

- Increasing low-level cloud cover late tonight into Monday morning, with locally dense fog possible.

- Light rain or drizzle Monday night into early Tuesday.

- Turning cold and blustery Wednesday with wind gusts > 35 mph, potentially paired with a few flurries.

- Unseasonably cold temperatures (highs in the 30s) continue on Thanksgiving and through the end of the week, with wintry precip becoming increasing likely next weekend.

UPDATE

Issued at 920 PM CST Sun Nov 23 2025

Clear skies, calm winds, and dewpoints in the 20s have allowed temperatures to tank outside of the urban Chicago core this evening. Have commensurately adjusted near term temperature trends downwards. Later overnight, thickening cirrus cloud cover and an incoming surge of moist air should help temperatures level off or even rise a bit.

Have expanded the fog mention across the area late tonight and through Monday morning, particularly for areas southwest of a roughly Rockford to Watseka line. Dewpoints across downstate Illinois and northeast Missouri are surging into the low to mid 40s as winds are turning southeast to south. This moist surge is helping drive a northward-expanding region of very low stratus and fog which will continue to slowly ooze northward through the night. Earlier, had wondered if increasing flow in the lowest 50 mb might help temper the fog threat in our area. However, based on upstream observations across southern Illinois, this does not appear to be the case, with numerous sites reporting visibilities under 3/4 mile. Forecast soundings depict a notable near-surface hydrolapse accompanying this moist surge, with most of the flow immediately above this layer.

Based on ongoing trends, can't rule out the potential for a Dense Fog Advisory at some point across the southwest half of the area towards daybreak Monday morning. Don't have any plans to tackle that right now given lingering uncertainties with the near-surface flow's impact on fog trends, however. Thankfully, this moist layer appears too thin to result in any drizzle potential at this time.

Finally, have adjusted temperatures in our west down a bit with the thinking that this stratus layer will have some staying power. Across our far south and northwest Indiana, filtered sunshine may allow temperatures to push into the low to mid 50s, but will note there remains a significant bust potential on the high temperature forecast tomorrow.

Carlaw

DISCUSSION

Issued at 230 PM CST Sun Nov 23 2025

A broad surface high centered over southern Illinois has yielded a sunny and seasonably mild day across the region, with mostly clear skies remaining through the evening amid light SSW winds.

A persistent band of thick stratus from central Missouri to western Kentucky today will become a focus tonight and especially Monday as low-level moisture advection takes hold across the mid-Mississippi River Valley. Expectations are for the stratus to expand NNE under a developing shallow inversion from ongoing WAA. Added weak isentropic ascent within and below this inversion should bring low stratus (possibly LIFR ceilings and locally dense fog) into at least southwest portions of the CWA prior to daybreak, and possibly across the entire CWA by mid-morning. Where the northern edge of the stratus resides by this time will dictate temp trends as diurnal erosion of the clouds is likely given the expected shallow cloud depth. But with thickening cirrus also spreading northward through the day, erosion of any cloud cover will be notably slower than what was observed farther south today. Have maintained a somewhat middle ground with max temps in the upper 40s on Monday, but thick stratus would support temps in the low to mid 40s and little stratus would favor highs in the mid 50s.

Continued low-level WAA and some diurnal heating below mid/upper-level diffluence will lift and weaken the low-level inversion late in the day and especially Monday night into Tuesday morning, which will support at least some areas of light rain or drizzle for most locations. However, a disjointed placement up the main upper-level trough crossing southern Wisconsin and the mid-level wave crossing the south half of Illinois may result in a minimum of precip coverage and QPF across most of northern Illinois during this period.

A potent cold front will then sweep across the area Tuesday evening, ushering in much colder and blustery conditions overnight through Wednesday. A modest isallobaric component mostly aligned with the gradient flow combined with added diurnal mixing will support the potential for wind gusts nearing wind advisory criteria (gusts of at least 45 mph) on Wednesday. Additionally, the depth of expected stratocumulus should be sufficient for isolated to scattered snow showers (or at least flurries) in the morning and possibly into the afternoon. Cold and somewhat blustery conditions will persist for Thanksgiving Day, with the incoming cold airmass suggesting that max temps both Thanksgiving and Friday will struggle to rise much above freezing each afternoon.

Kluber

A much more active weather pattern will take hold across the central CONUS this weekend and into the first week of December. Overall, the larger scale pattern across North America continues to favor upper troughing setting up across the western CONUS and upper ridging across the southeastern CONUS during this period. The presence of greatly enhanced southwesterly mid and upper level flow into the lower Great Lakes in such a pattern is notorious for steering numerous impulses across our region. Accordingly, some periods of active weather, with rain and/or snow is possible as we head into next weekend. Ensemble solutions have steadily zoned in on a late Saturday into Sunday period for potential wintry precip, including accumulating snow. It is important to note that while the pattern looks increasingly active, the finer scale details this far out remain largely unclear and will need to be ironed out in the coming days. For example, the potential wintry weather next weekend will depend on phasing of a trough currently just east of the Kamchatka Peninsula (that will also have to round the Aleutian Low) and another trough halfway between Hawaii and California. Nevertheless, this period will be monitored closely for potentially impactful weather systems across the central CONUS that could impact holiday travel. Stay tuned.

KJB/Kluber

AVIATION /06Z TAFS THROUGH 12Z TUESDAY/

Issued at 1119 PM CST Sun Nov 23 2025

Forecast concerns include...

Ifr/lifr cigs Monday with mvfr/ifr vis/fog. Chance of showers Monday afternoon/evening. Light rain/drizzle/ifr/lifr cigs/vis Monday night.

A large area of lifr/vlifr cigs/vis continues to expand and lift north across southeast IA and southern IL late this evening. There is also fog developing across central IL, ahead of the main area of cigs/lower vis. Guidance has slowed the progression north and also shifted it just a bit west, possibly keeping it west of ORD/MDW/GYY. Confidence is too low to make any significant changes to the current forecast and maintained tempo lifr cigs for ORD/MDW/GYY Monday morning. If it were to occur, likely around and after sunrise. Its more likely there could be some scattering/lifting of these cigs by afternoon as well.

Further west, especially RFD, there is increasing confidence that at least ifr cigs may become prevailing through much of Monday with a period of ifr vis around/after sunrise. There could be vis under 1sm for some areas, especially southwest of the terminals. These lower conditions may improve some by midday/early afternoon. There may also be a few showers Monday afternoon, mainly across northwest IL.

Cigs/vis are expected to expand east and lower through Monday night with prevailing lifr/ifr cigs by early Tuesday morning areawide. Periods of light rain and drizzle are also possible late Monday evening into Tuesday morning.

Mainly southerly winds are expected through sunset Monday evening, favoring south/southwest on Monday and then turning south/southeast Monday evening. Directions may continue turning more southeast Monday night and possibly easterly early Tuesday morning. Speeds into the 10kt range by daybreak are still expected and where clouds scatter on Monday, speeds 10-15kts with a some higher gusts are possible. cms

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...None.