textproduct: Central Illinois

KEY MESSAGES

- Chilly conditions will prevail tonight: however, the risk for a hard freeze has decreased substantially due to expected cloud cover. Low temperatures will be coldest along the I-74 corridor where readings will bottom out around 30 degrees.

- An upper disturbance will produce a band of light rain and snow along and south of a Macomb...to Decatur...to Mattoon line late tonight into early Tuesday morning. Less than 1 inch of snow is expected on grassy surfaces.

- Warmer/wetter conditions will return by the end of the week: however, severe weather is not anticipated.

DISCUSSION

Issued at 247 AM CDT Mon Apr 6 2026

Cold Tonight...

As has been advertised for the past several days, the coldest period of the forecast will occur tonight. High pressure currently extending from Saskatchewan into the Dakotas will settle southeastward tonight...and is progged to be centered over Wisconsin by 12z Tue. Meanwhile an upper-level disturbance tracking out of the Plains will spread clouds across much of central Illinois tonight. Given the expected cloud cover and northeasterly winds of 5-10mph on the southern periphery of the high, radiational cooling will not be ideal. As a result, several CAMs have trended much warmer...with the 00z Apr 6 RRFS showing lows staying in the middle 30s along I-74. The HRRR is not quite that warm, but still only indicates minimum temps around 30-32 degrees across the N/NE KILX CWA. While sub-freezing temperatures are still possible, confidence is growing that a widespread hard freeze with temps dipping into the 20s will not occur. Will leave the current Freeze Watch in place for locations along/north of a Macomb to Danville line, but this will likely be cancelled by later shifts if trends continue. The latest forecast will feature lows ranging from around 30 degrees along/north of I-74 to the middle to upper 30s south of I-70.

Light Rain/Snow Tonight...

As a short-wave trough tracks out of the northern Rockies and interacts with the trailing end of the departing frontal boundary, a narrow band of precipitation will develop tonight into Tuesday morning. 00z Apr 6 models are all in good agreement concerning the placement of the band from eastern Nebraska across southern Iowa/northern Missouri into south-central Illinois. Will need to keep a close eye on later model runs, because some minor track adjustments are still possible. Specifically in central Illinois, the latest model consensus suggests the precip will occur along/south of a Macomb...to Decatur...to Mattoon line...with the most significant precip staying along/south of a Rushville to Springfield line. The NAM shows the strongest frontogenesis developing within the 800-700mb layer between 06z and 12z, with the forcing weakening considerably by 15z Tue. While the airmass will initially be quite dry, the combination of increased forcing and weak upglide noted on the 300K surface will lead to the development of light precip primarily after midnight into early Tuesday morning. The thermal profile will initially be warm enough to support rain: however, ample evaporative cooling will allow the precip to mix with and/or change to all snow overnight. Snowfall will remain light due to the initial mixed phase of the precip, marginally cold air temperatures, and the warm ground. 00z Apr 6 HREF mean snowfall is less than 1 inch...while the HREF max features as much as 1-3 inches across the far SW CWA. At this time, will forecast amounts of less than 1 inch on grassy surfaces along/south of a Rushville to Springfield line.

Warmer/Wetter by the End of the Week...

The current northwesterly flow pattern will be replaced by a flat west-to-east zonal flow by the middle and end of the week. This will allow temperatures to climb back above normal and also introduce increased rain chances as a series of disturbances track across the CONUS. The primary challenge with this type of scenario is trying to predict exactly where the main baroclinic zone will lay out. As the first short-wave approaches, it will drag a cold front toward central Illinois on Thursday...with the boundary then going parallel to the upper flow and becoming quasi-stationary after that. Models are showing a good deal of spread concerning placement of the boundary Friday through Sunday, so current NBM features daily rain chances through the period. It will most definitely not rain that entire time, and PoPs will be adjusted accordingly as details become clearer.

After a chilly day with highs only in the 40s on Tuesday, readings will climb back into the upper 60s/lower 70s Wednesday through Friday...then will soar well into the 70s to near 80 degrees by Sunday as the flow becomes more southwesterly. Tuesday/Wednesday will be dry days...with rain chances north of I-72 on Thursday, then everywhere Friday through Sunday. While showers and thunderstorms are in the forecast, the risk for widespread severe weather will remain low due to marginal instability and the lack of a strong upper forcing mechanism.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

Issued at 535 AM CDT Mon Apr 6 2026

VFR conditions will prevail through the entire 12z TAF period. FEW-SCT mid-level clouds at 10,000-12,000ft will stream across the sky through early afternoon, then will become BKN-OVC between 21z and 00z. A weak disturbance is expected to trigger a band of lower clouds and light precip across northern Missouri into southwest Illinois late tonight. The exact placement of the band is still in question: however, it appears it will remain largely S/SW of the central Illinois terminals. It will come close enough to warrant VCSH at KSPI after 06z, with dry conditions elsewhere. Winds will become NW with gusts of 20-25kt later this morning as a cold front drops through the region. Winds will decrease to around 10kt by sunset, then will gradually switch to N/NE after midnight.

ILX WATCHES/WARNINGS/ADVISORIES

Freeze Watch from late tonight through Tuesday morning for ILZ029-031-036>038-041>046.