textproduct: Central Illinois

KEY MESSAGES

- Dry and cold conditions continue tonight with temperatures dropping into the teens. Areas with clear skies may see temperatures fall into the single digits as well as patchy fog.

- A late-week warm-up begins Thursday as temperatures rise above freezing for most areas west of I-55. Friday will be the warmest day, with high temperatures reaching the upper 30s to mid-40s.

- Winds will increase Friday afternoon following a cold front. Expect northwest wind gusts up to 30 mph through the early evening.

- Above-normal warmth returns early next week. There is a 50% to 80% chance that temperatures will reach at least 50 degrees between Monday and Wednesday.

UPDATE

Issued at 848 PM CST Wed Feb 4 2026

Updates have been sent for trends in cloud cover this evening, with clearing over most of the area aside from areas southeast of Taylorville to Champaign. In addition, clear skies developing as a result of high pressure moving over the area will bring a potential for fog forming for a time overnight and possibly lingering into the morning. A few models indicate an area around a Decatur to Champaign line as a favored area for fog overnight, which seems reasonable given recent cloud cover trends. A caveat is cloud cover spreading into the area from the northwest after midnight, associated with a shortwave moving toward the Great Lakes, that could limit radiational cooling and limit fog formation. With this evening's update, patchy fog has been added to areas from around Decatur to Champaign into east-central IL. Otherwise, lows around 10 for east-central IL and 12-15 west of I-55 look on track for tonight.

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DISCUSSION

Issued at 134 PM CST Wed Feb 4 2026

SHORT TERM (Tonight through Thursday Night)

A 1030mb surface high is currently centered over the Upper Midwest and will slowly drift southeast, inching toward and across Central Illinois overnight through Thursday. This high pressure will maintain dry and cold conditions across the region. Lows tonight will dip into the teens across most of central Illinois, but areas that experience significant clearing could quickly fall into the single digits under a strong radiational cooling setup.

Meanwhile, a downsloping event is ongoing across the northern Rockies, where surface temperatures lee of the range are running well into the 50s and 60s in some locations. 850mb temperatures are forecast to warm dramatically to 13-17C across portions of southern Alberta into Montana this evening. This much warmer air mass will advect southeast, clipping portions of Central Illinois Thursday and continuing into early Friday, ahead of an approaching cold front. The result will be a late-week warm-up. Widespread temperatures above the freezing mark are expected (NBM 70-95% probability) west of I-55 on Thursday.

A series of shortwaves are progged to dig across the region, the first tracking across northern Illinois midday Thursday. Dry low and mid-levels will be difficult to overcome locally, with the main forcing offset just to our north. Still, areas near the I-74 corridor cannot completely rule out some very light snow or even some patchy drizzle, as soundings suggest a loss of ice nuclei at times. Confidence in measurable precipitation remains low, with only a 20% PoP north of the I-74 corridor late morning into the early afternoon.

LONG TERM (Friday through next Wednesday)

The late-week warm-up peaks on Friday before a cold front pushes through. Widespread temperatures above freezing are expected area- wide (NBM >95% probability). NBM mean MaxT Friday ranges from the mid 40s near the lower Illinois River Valley to upper 30s across east central Illinois.

A second shortwave takes a very similar track Friday afternoon with an attendant surface cold front pushing south across central Illinois late morning and afternoon. Antecedent dry conditions remain difficult to overcome, and PoPs remain low as a result, only around 10 percent along and north of the I-74 corridor. Moderate northwest winds develop behind the cold front with gusts to around 30 mph during the afternoon and early evening.

Another moderately strong area of high pressure will build in behind the cold front, tracking from the Canadian Prairies Friday across the Midwest over the weekend. Temperatures will return closer to seasonal norms Saturday, with highs generally in the 30s and lows in the 20s. More recent guidance has become zonal aloft and progressive with the surface features, and now pushes the ridge axis all the way to the mid-Atlantic Coast by late in the weekend. Return flow behind the ridge axis will begin to overspread central Illinois Sunday, while aloft, flat ridging builds across the region. This pattern shift will allow temperatures to trend back above normal starting Sunday afternoon, with 40s and 50s returning to the forecast through the first half of next week. NBM probabilities for reaching at least 50 degrees increase to 50-80 percent west of I-55 on Monday, with similar percentages across the entire forecast area for Tuesday and Wednesday.

Deubelbeiss

AVIATION

(For the 06z TAFs through 06z Thursday Night) Issued at 1035 PM CST Wed Feb 4 2026

Clear skies and light winds may allow fog to form in parts of central IL overnight before increasing cloud cover arrives from the northwest ahead of an approaching weather disturbance. This looks to target mainly KDEC-KCMI as high clouds already start arriving early in the morning in areas to the northwest to limit radiational cooling. A weather system passing by to the north could bring some light snow showers along and north of I-74 late morning into afternoon, and have PROB30 for MVFR cigs with this feature from KPIA-KBMI-KCMI around 16Z-21Z. Winds light and variable, becoming SW around 10 kts by 15Z.

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ILX WATCHES/WARNINGS/ADVISORIES

None.