textproduct: Central Illinois

KEY MESSAGES

- Well above normal temperatures are forecast through Saturday across central and southeast IL. Highs of 60 to 65 expected in southeast IL today through Thursday, with the warmest readings in the 60s expected over much of area on Friday and Saturday, with southeast IL approaching 70F (NBM 50-70% chance).

- There is a chance of light rain showers, along with patchy fog and drizzle Wednesday afternoon into early Thursday morning. Rainfall amounts should stay less than a tenth inch if they occur. - A strong storm system passing over the northern Great Lakes region Saturday night and Sunday to bring a strong cold front southeast through IL overnight Saturday night, with much colder temperatures early next week.

DISCUSSION

Issued at 330 AM CST Tue Dec 23 2025

The 09Z/3 am surface analysis shows a cold front over central parts of WI and Iowa and into far nw MO. South to SW winds 7-14 mph and few gusts 17-23 mph with temps ranging from upper 40s and lower 50s in southeast IL from Charleston/Mattoon southeast to 35-40F over the IL river valley with Mt Sterling down to 33F. Low stratus clouds with bases around 1k ft are near the Wabash river valley and drifting eastward. High cirrus clouds have quickly spread eastward over central and northern IL, with thicker high clouds from I-74 north.

Latest CAMs show cold front to push southeast toward the IL river valley by late morning, and through rest of central IL during this afternoon, passing thru southeast IL after sunset (late afternoon and early evening). Limited moisture and lift with the front so still expected to pass through dry with a period of partly to mostly cloudy skies, though more sunshine sw CWA. Mild highs near 50F over Knox, Stark and Marshall counties, and lower 60s in southeast IL from I-70 south. SW winds 5-15 mph and few gusts to 20 mph into mid morning, to switch nw to north behind cold front and diminish light by sunset as 1028-1030 mb Canadian high pressure over Saskatchewan drifts into the upper MS river valley. High pressure to move over lower MI and Ohio by sunrise Wed and mostly clear to partly cloudy skies and light winds. This gives cooler lows in the low to mid 30s in central IL (coolest from I-74 north) and 35-40 in Southeast IL. A few members like RAP13 and HRRR show patchy fog overnight sw CWA but kept out of forecast for now. Low clouds to be sw of CWA tracking ne toward the MO/IL border by dawn Wed. These low clouds to then spread ne across central IL later Wed morning and afternoon as front lifts back north as a warm front with SE winds and could have 20-40% chance of light rain Wed afternoon along with patchy fog and drizzle from low stratus clouds. Highs Wed range from upper 40s from Macomb to Bloomington north to the upper 50s/lower 60s in se IL. Models have trended cooler for Wed into Thu with 60s more confined to southern/se IL.

Another Canadian high pressure building into Ontario on Christmas Day to push the front back south over central IL Wed night and this may be our best chance of rain showers along with drizzle and fog. Models have trended slower with lifting front back north as warm front on Thursday with east to NE flow much of the day, so highs in upper 40s/lower 50s from Macomb to Bloomington north while 60-65 in southeast IL. A weak surface low tracking through northern IL/IN to have west to SW flow over area and possibly our warmest day this week with 60s Macomb to Bloomington to Rantoul south and upper 50s north. Southeast IL could reach close to 70F with NBM having 50-70% chance of this possibility. Similar temperature structure on Sat with mild air continuing into Sat evening.

A strong and strengthening surface low passing north of Lake Superior during Sat night to push a strong cold front se through the CWA during Sat night. Models and their ensembles show 20-30% chances of showers by overnight Sat night in eastern/se IL with high pops further east and se of IL. Blustery NW winds develop behind the cold front overnight Sat night and Sunday with gusts 25-35 mph. This brings in much colder air with highs Sunday in the lower 30s from I-55 nw and lower 40s in southeast IL. Coldest air arrives Sunday night into Monday night as strong Canadian high pressure builds into the MS river valley Monday night. Lows in the low to mid teens both Sunday and Monday night, and subfreezing highs Monday in the low to mid 20s and lower 30s next Tuesday.

The Climate Prediction Center (CPC) 6-10 Day Outlook for Dec 28 thru Jan 1 has a 40-50% chance of above normal temperatures over central and southeast IL, with a 50-60% chance of above normal temps over west central and sw IL. Near normal precipitation trends are expected over IL. CPC 8-14 Day Outlook for Dec 30-Jan 5 has a 60-65% chance of above normal temperatures with 33-40% of above normal precipitation over IL.

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AVIATION

(For the 12z TAFs through 12z Wednesday Morning) Issued at 550 AM CST Tue Dec 23 2025

Aside from MVFR visibilities (3-5 miles) in patchy fog at CMI and possibly DEC until 14-15Z, VFR conditions should prevail next 24 hours across the central IL airports. Weak cold front to push se through central IL from 15-18Z, while Canadian high pressure over southern Saskatchewan settles over the upper Great Lakes and ridging southward into IL overnight. Will see some passing cirrus bands today and being more scattered later this afternoon and evening before broken cirrus clouds spread back east early overnight. SW winds around 10 kts early this morning to shift west to WNW at PIA by 15Z, and at DEC and CMI from 17-18Z. Winds turn more NW during the afternoon, and diminish to 4-9 kts and veer north by early evening and ENE later tonight and increase a few kts toward daybreak Wed. A few of the CAM members like HRRR and RAP13 show very patchy fog developing overnight, but coverage appears too limited with dry low levels along with some wind flow from surface to 925 mb.

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ILX WATCHES/WARNINGS/ADVISORIES

None.