textproduct: Central Illinois

KEY MESSAGES

- Wind chills are not forecast to climb above the single digits until mid Tuesday morning, and they may (30-40% chance) fall below 0 again this evening in spots. Those venturing outdoors should wear extra layers to prevent frostbite and hypothermia.

- Seasonably cool and mostly dry conditions are forecast the next 7 days. The highest precipitation chances will be Wednesday evening, when there is a 30-40% chance of light snow near and north of I-74.

DISCUSSION

Issued at 100 PM CST Mon Dec 29 2025

***** COLD TONIGHT *****

The 979mb sfc low over eastern Ontario/western Quebec will continue to pull away to the northeast, and high pressure will slowly shift into the MS Valley through tonight. As a result, northwest winds, currently 15-25 gusting to 35+ mph, will ease to 5-15 mph after midnight. With multiple weak perturbations rotating about the periphery of the expansive upper level low, it's unclear when skies will clear across our area tonight, but HREF guidance suggests the chances are high (80-90%) west of a Peoria to Effingham line by about 1am. These areas will cool the most overnight, with lows possibly (20-40% chance, per NBM and HREF) dipping into the single digits northwest of Peoria. We leaned towards the lower end of the ensemble envelope on temperatures tonight across our western counties where chances for clearing are highest, but how quickly winds diminish (a low-confidence part of the forecast) will be key. In any case, wind chills will remain in the single digits above/below 0 area-wide through mid Tuesday morning.

***** SEASONABLY COOL, SLIGHT SNOW CHANCES WEDNESDAY *****

Conditions will turn less cold tomorrow as weak warm advection returns, bringing highs into the upper 20s along the I-74 corridor to low-mid 30s southwest of Springfield. Wednesday, we should add a couple more degrees to highs with mid 30s forecast area-wide.

Another trough diving southeast out of northern Ontario will bring arctic air south across the Great Lakes, potentially grazing our area with another glancing blow of cold Wednesday night into Thursday. Ahead of the cold air, a clipper is slated to drop snow across southern Wisconsin and northeast IL. Being this is a few days out, lots is subject to change in the path of this clipper (and hence snow), but it currently appears the greatest chance for accumulating snow would be along and northeast of I-74 where LREF and NBM depict a 30-40% chance for anything measurable (i.e., a tenth of an inch or more).

The rest of the forecast period, seasonably cool conditions and low chances for precipitation are expected. The ECMWF Extreme Forecast Index (EFI) generally stays below 0.6 during this time period, indicating no noteworthy signal for anomalous, high-impact weather.

Bumgardner

AVIATION

(For the 00z TAFs through 00z Tuesday Evening) Issued at 500 PM CST Mon Dec 29 2025

Satellite imagery showed decreasing cloud coverage as the sun set, but lingering MVFR cloud streets appear persistent enough to warrant holding onto MVFR ceilings in the TAF. I'd expect ceilings to bounce between MVFR/VFR during the first few hours of the period before improving to VFR by late evening. West-northwest wind gusts will continue to gradually diminish into tonight. Into Tuesday, winds turn to southwesterly, around 10 kts, and broken mid-level (VFR) cloud cover overspreads the area from north to south. Aside from a few flurries at the start of the period, precip is not expected this period.

Erwin

ILX WATCHES/WARNINGS/ADVISORIES

None.