textproduct: Central Illinois

KEY MESSAGES

- Gloomy conditions continue, with widespread rain overnight (90% chance) and areas of fog and drizzle lingering into Tuesday. Widespread dense fog is unlikely tonight, with just a 20-30% chance of visibility below a half mile.

- Strong northwesterly wind gusts are expected on Wednesday, with a 60-80% chance for gusts over 40 mph. A Wind Advisory may be needed. The greatest impact of the winds will be felt on north- south oriented roadways like I-55, I-57, and I-39.

- A cold front moves through Tuesday night, resulting in sharply colder conditions for Wednesday through Friday. Highs for Thanksgiving will only be in the 30s.

- A weekend system is expected to bring a mix of precip, including rain and snow. The exact timing, precipitation types, and accumulation amounts remain subject to change, but there is a 20-50% chance of 2" of snow. Those with travel plans this weekend should continue to monitor for updates.

DISCUSSION

Issued at 144 PM CST Mon Nov 24 2025

A rather active pattern will exist over the next week as upper flow remains unblocked. The key items include rain/fog over the next 24 hours, windy conditions on Wednesday-Thursday, and a snow chance over the weekend.

*** THROUGH TUESDAY NIGHT ***

Gloomy conditions appear likely to persist through at least late morning, if not midday, on Tues. A shortwave was located over S KS Mon afternoon, with the associated sfc low over OK. This system will lift northeast towards IL tonight. Forecast soundings show the atmospheric column becoming deeply saturated, as WAA and LLJ forcing lead to rain overspreading the region. The latest CAMs suggest rain will be most widespread between about midnight and 3 AM east of the IL River (80-90% chance). Modest rainfall totals are expected through sunrise on Tues, with a 50-70% chance of exceeding a quarter inch (highest south of I-70), but less than a 10% chance of exceeding one inch. The thick cloud cover will limit nocturnal cooling, resulting in seasonably mild low temps in the mid/upper 40s.

Forecast soundings show persistent low-level saturation well into the day on Tues, so the thinking is stratus, fog, and perhaps drizzle will be a common feature into Tues AM. Some patchy dense fog can't be ruled out, but guidance is not as widespread with the dense fog as it was Mon AM. HREF guidance has a 20-30% chance of visibility below a half mile. With widespread cloud cover expected, nudged highs a bit cooler for tomorrow, still in the 50s.

Tonight's low pressure system will be followed quickly behind by a wave digging over the northern Plains, deepening as it does so. This will result in a sfc low tracking across central WI Tues PM, sending a strong cold front barreling across IL late Tues eve. A broken line of rain is expected to accompany the front (20-50% chance), but instability values are very low (less than 100 J/kg) so it appears unlikely we'll hear any rumbles of thunder. Temps will drop sharply Tues night, as breezy west-northwesterly winds advect a much cooler airmass into the region. By early Wed AM, air temps are forecast to be around freezing, while the winds will drop apparent temps into the low 20s.

*** WEDNESDAY - FRIDAY ***

After the aforementioned cold front moves through Tues night, well below normal temps are expected to persist through Fri with highs near 40 on Wed, then firmly in the 30s for Thurs/Fri. These temperature values are more typical of late December/early January. From Wed AM through the daytime hours on Friday, precip chances are less than 15%.

In addition to temps, the other concern is strong west- northwesterly wind gusts, particularly on Wed as the deepening low over the Great Lakes results in a tight pressure gradient across the Midwest. Both pressure rises and diurnally-driven mixing will support vertical transport of strong winds at the top of the boundary layer down to the sfc. Fcst soundings suggest 40-50 mph gusts are firmly in the range of outcomes, and ECMWF Ens supports this with an 80% chance for peak gusts over 40 mph from Fulton to Edgar Counties and northward. While the probability of exceeding wind advisory criteria (gusts over 45 mph) is marginal (20-40%), would not be surprised if an advisory is eventually issued due to potential impacts on a high travel day. Regardless of whether or not a wind advisory is issued, those with travel plans on Wed should be prepared for gusty winds, especially if traveling on north-south oriented interstates like I-55, I-57, and I-39. Similar or slightly stronger wind gusts are expected as you travel northward on Wednesday, while gusts gradually weaken further to the south.

Wind speeds/gusts will gradually trend weaker each day as the sfc low shifts away, but Thanksgiving will remain somewhat breezy with peak gusts as high as 30 mph. Given the combination of cold airmass and breezy winds, those with outdoor plans Thanksgiving morning (Turkey trots, parades, etc) will need to bundle up, as apparent temps are expected to be in the teens. The coldest temps are actually expected Fri AM, as broad sfc high pressure setups near the I-29 corridor (far eastern Plains). This will lead to better radiational cooling, dropping air temps into the teens Fri AM.

*** WEEKEND SYSTEM ***

A potentially impactful system continues to appear possible this weekend, with wintry precip accumulations in the range of outcomes. It's important to note, however, that this system is still well offshore of the CONUS in the form of a smattering of upper disturbances currently positioned near the Aleutians Islands (over 2,000 miles away).

Given the importance of both precip timing and low-level thermodynamic profile with a system like this, the specific evolution remains low confidence at this range. We continue to lean heavily on ensemble guidance for messaging. The ECMWF and its ensemble are the faster (and snowier) solution, with the ensemble showing a 50-80% chance of 3" of snow north of I-70 over the weekend. (Conversely, the GEFS is at 20-40% chance of over 3"). The ECMWF-based "shift of tails" also highlights much of the ILX CWA, indicating that at least 10% of ensemble members depict an extreme event. The NBM 90th percentile snowfall (10% chance of higher) captures some of these more extreme outcomes, suggesting values as high as 5-8" are possible in a reasonable worst case scenario. On the flip side, the NBM 10th percentile (90% chance of higher) has virtually no snowfall, which is a good encapsulation of the ongoing uncertainty with this system. For the sake of monitoring trends in the deterministic data, will note that current forecast soundings show WAA leading to the development of a low-level warm nose, but sfc temps also quickly rise around the same time, resulting in little to no window of freezing rain (just rain or snow). That's not to rule out freezing rain, but simply note that current guidance doesn't depict it as much of a concern. The NBM probability of a trace of ice is less than 10% area-wide through the weekend.

Those with travel plans this weekend are urged to monitor forecast updates as this system comes into better focus.

Erwin

AVIATION

(For the 00z TAFs through 00z Tuesday Evening) Issued at 559 PM CST Mon Nov 24 2025

Despite some improvement in conditions in parts of central IL this afternoon with areas of MVFR and even localized IFR conditions, an approaching weather system will bring deteriorating conditions again this evening, with more widespread rain developing, and cigs becoming LIFR. As rain diminishes early in the morning, drizzle and fog is expected to linger, with LIFR conditions continuing for several hours. Improvement is expected to be very gradual, with IFR not expected to be reached until after 19Z-21Z. Continued improvement looks on track for very late in the period, with potential for at least brief VFR Tuesday evening. Winds SE 5-10 kts becoming light and variable by 06Z-12Z. Winds returning from W 5-10 kts by around 18Z.

37

ILX WATCHES/WARNINGS/ADVISORIES

None.