textproduct: Central Illinois

KEY MESSAGES

- Inclement conditions are expected tomorrow, with breezy winds and a high chance of rain (over 90%). Despite a mild start, temperatures will fall sharply during the day as a strong cold front sweeps across the region.

- Snow showers with the potential to limit visibility and create slippery evening commute conditions are forecast from 4pm to 9pm tomorrow evening.

- The wind gusts tomorrow may approach 45 mph at times. Winds will be out of the south during the morning, then out of the west-northwest during the afternoon and evening.

- Temperatures fluctuate through the weekend. The coldest conditions are expected Friday morning, when wind chill values will drop to near to below zero north of I-72. Above normal temperatures remain likely next week (70-80% chance).

DISCUSSION

Issued at 149 PM CST Wed Dec 17 2025

Today winds will shift to a more southerly flow, increasing the WAA and moisture return. No precipitation is expected for the remainder of the day. A low pressure system is deepening over the northern Plains today, strengthening the pressure gradient over the mid- CONUS. Winds will begin picking up overnight, ahead of the cold frontal passage tomorrow morning. The stronger, southerly winds will increase the WAA overnight. Because of the timing of this system, temperatures will act in a non-diurnal way. The high for tomorrow (46-55 degrees) will occur in the morning ahead of the cold front, then will decrease throughout the day. Winds will continue to be strong behind the front, but from the NW instead. CAA will be decent, bringing in below to near freezing temperatures back to the forecast area for Friday.

Focusing a little closer on the winds for tonight into tomorrow, we can take a look at the probabilistic ensembles. A strong low-level jet will set up over Illinois with 60 mph winds a few thousand feet AGL. The HREF is likely over mixing, therefore showing too high of wind gusts. The NBM is showing 40-50% chance of wind gusts exceeding 35 mph through tomorrow morning. As the front passes through, showers and potentially some rumbles of thunder are expected. Some of these showers/t'storms could get near severe if they can successfully mix down the very strong winds from the LLJ. Later in the day tomorrow, winds will pick back up again. After 00z, wind gusts over 30 mph are possible north of I-72, with a 40-70% chance of greater than 35 mph wind gusts. Winds will relax as we move into Friday morning.

Behind the front tomorrow afternoon into the evening, we could see some snow showers as the CAA drops the temperatures. Overall, amounts from the showers should remain minimal, around maybe a tenth or two. However, there is a signal for the potential of snow squall development. There is a decent area of FGEN around 00z-03z based off the models, with 30-40 J/kg of instability (SBCAPE) and >1 snow squall parameter co-located. Timing for development is from 22z Thursday to 03z Friday (4pm-9pm Thursday). Snow amounts aren't expected to be high, maybe a couple tenths for the most part with the showers. With any snow squall that develops rapidly deteriorating road conditions and limited visibility. When heading home for the evening tomorrow, stay aware of the weather and its impacts.

Dry weather will settle in for the weekend by Friday morning. Highs will bounce around this weekend before leveling out by mid-week. Friday highs will be in the low to mid 30s, with lows in the teens that morning. Saturday will warm up into the upper 40s to low 50s, with lows in the 20s. Sunday will drop back into the upper 30s to low 40s, with lows in the 20s. By Tuesday and Wednesday, temperatures will get back int to upper 40s to upper 50s.

Copple

AVIATION

(For the 06z TAFs through 06z Thursday Night) Issued at 1108 PM CST Wed Dec 17 2025

Winds from the southwest will become gusty overnight due to a tightening pressure gradient preceding an approaching front. Conditions are already deteriorating rapidly with ceilings dropping to MVFR/IFR and the development of a strong low- level jet.

Overnight, surface wind gusts will peak around 25 kt, while winds at 2,000 feet are anticipated to approach 50-55 kt.

Drizzle will become widespread prior to 09Z, with the heavier rain occurring with the frontal passage after 13Z. Gusty winds will be a feature of the showers and frontal passage, with surface gusts potentially reaching 45 kt in the strongest activity. A low probability (less than 20% chance) of a few rumbles of thunder exists with the frontal passage. Following the front, winds will shift to the west and remain gusty through the afternoon.

With this TAF cycle, we have introduced mention of snow showers across all terminals by 00z Friday. The probability remains low/medium (20-50%), but we wanted to signal some impact in what might be the return of IFR condtions.

MJA

ILX WATCHES/WARNINGS/ADVISORIES

None.