textproduct: Central Illinois

KEY MESSAGES

- A Winter Weather Advisory is in effect for all of central and southeast Illinois through tonight. Snowfall everywhere north of the I-70 corridor will range from 2 to 4 inches...with locations further south picking up 1 to 2 inches.

- Much below normal temperatures will prevail through next weekend...with the coldest readings arriving Thursday night when 12z NBM guidance suggests a 60-80% chance of lows dipping below zero along and north of a Rushville to Mattoon line.

UPDATE

Issued at 743 PM CST Mon Dec 1 2025

An upper shortwave trough is approaching the Middle Mississippi Valley this evening. Large-scale ascent and frontogenetic forcing out ahead of the wave has resulted in light to moderate snowfall since early this afternoon. Snowfall totals up to this point have ranged from around 1 to 3 inches. Short-term guidance shows a stronger 700-800 mb frontogenetic band lifting through the area over the next few hours, with a more defined snow band associated with this feature setting up from roughly Springfield to Champaign just before 8 pm. Additional snow amounts under this band could approach 2 inches as it slides east across the area, with 0.5 to 1 inch per hour snowfall rates. Snow will exit from west to east later tonight, clearing Galesburg around 10 pm and closer to Lawrenceville by 2 am.

NMA

LONG TERM

(Wednesday through Next Monday) Issued at 226 PM CST Mon Dec 1 2025

Wednesday appears to be the warmest day of the forecast period as boundary layer winds become southwesterly ahead of an approaching cold front. Thickness values support a warm-up well into the 40s: however, the snow cover and continued cloud cover across much of the area will curtail the warming. Am still expecting highs to rise above freezing and lead to some melting of the recent snow. As the front nears, all models are showing scattered snow-showers northwest of the I-55 corridor by late Wednesday afternoon, then further east across the remainder of the area during the evening. Little to no snow accumulation is expected. Once the front passes, windy and sharply colder conditions will arrive for Thursday. The good news is that the sun will finally return at that time, the bad news is that strong CAA will keep daytime highs in the teens north of I-70 and the lower to middle 20s to the south. The coldest period continues to look like Thursday night as winds diminish over the snow cover. 12z NBM guidance indicates a 60-80% chance of lows dipping below zero along and north of a Rushville to Mattoon line.

The southern stream storm system that the models had previously spread into Illinois by the end of the week has now shifted southward. Given the presence of the Arctic airmass, the more southern position of the prevailing baroclinic zone and storm track makes sense. As such, have removed Friday PoPs...except for just a slight chance (20%) south of I-70. As high pressure shifts to the east and boundary layer flow once again shifts to southerly ahead of the next approaching cold front, temps will briefly rebound into the lower to middle 30s on Saturday. After that, cold and dry conditions with highs in the upper 20s and lower 30s is anticipated for next Sunday and Monday.

Barnes

AVIATION

(For the 06z TAFs through 06z Tuesday Night) Issued at 1108 PM CST Mon Dec 1 2025

Conditions will improve somewhat later tonight as snow exits from west to east by 07z. IFR/MVFR ceilings will linger overnight, looking to improve to all MVFR by mid to late morning. Ceilings should improve late evening nearing the end of the period to VFR conditions. CMI will be the latest improvement, staying MVFR the whole period. Winds will be light through the 06z period with speeds generally below 10 kts.

Copple

ILX WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory until 6 AM CST Tuesday for ILZ027>031- 036>038-040>057-061>063-066>068-071>073.