textproduct: Central Illinois

KEY MESSAGES

- Patchy frost is possible tonight, with the highest chances (30-50%) north of a Macomb to Bloomington line. We recommend those with tender vegetation cover their plants to prevent damage.

- Periodic rain chances will continue through at least the middle of next week. The highest chances (20-30%) for thunderstorms will be Friday afternoon and Saturday night south of roughly I-72/Danville.

DISCUSSION

Issued at 150 AM CDT Wed May 6 2026

***** SPRINKLES LATE MORNING, PATCHY FROST TONIGHT *****

At 145am, showers were tapering from west to east across central and southeast Illinois. The RAP/NAM suggest 500mb flow will increase after dawn in response to phasing between a southern stream wave and northern stream trough, with perhaps sufficient lift to trigger a few sprinkles over central Illinois between 8am and noon. However, chances for measurable precipitation from the National Blend of Models (NBM) are understandably low given drying of low levels (below 10kft) evident in forecast soundings. Continued cool advection via northwest winds will confine high temperatures to the upper 50s to around 60, with overnight lows then sinking like a rock as skies clear and winds diminish. The High Resolution Ensemble Forecast (HREF) system gives a 30-50% chance that lows tomorrow morning fall below 37 degrees - an approximate frost threshold with light winds - north of a roughly Macomb to Bloomington line, with lower (but nonzero) chances elsewhere. Accordingly, we added patchy frost to the forecast and would encourage folks to cover tender vegetation to prevent damage.

***** FEW SHOWERS THURSDAY AFTERNOON, MORE RAIN FRIDAY *****

As high pressure shifts off to the southeast, we'll get a 10-20 mph westerly breeze which should add a few degrees to high temperatures (compared to today), with most/all of the county warning area (CWA) warming into the 60s tomorrow afternoon. A compact shortwave trough will pass through northern Illinois during the afternoon and evening, sparking a few light showers mainly north of a Macomb to Paris line. Forecast soundings show an inverted V featuring dry air below about 800mb, so it wouldn't be surprising if these generate locally gusty (40+mph) winds, but lack of deep moisture and instability suggests a negligible severe risk.

Weak warm advection resumes tomorrow night into Friday, with the Low Resolution Ensemble Forecast (LREF) system mean bringing 850mb temperatures back up to 6-8 degC by Friday morning. This is ahead of yet another shortwave trough, which will spark more numerous showers area-wide and a low (20%) chance for a thunderstorm or two south of I-72/Danville during the afternoon and evening. Cloud cover and precipitation should keep temps in the mid 60s to low 70s for highs Friday, but with returning warm advection on Saturday (southwest winds gusting to 25 mph) we should warm solidly into the 70s; in fact, NBM even advertises a 30-40% chance for 80+ degree highs in west-central Illinois.

***** MORE SHOWERS SATURDAY NIGHT INTO SUNDAY MORNING *****

Yet another shortwave trough is slated to dive across the Midwest and Great Lakes Regions Saturday night into Sunday, sparking another round of shower chances (40-60%). If the area gets a bit of elevated instability, we may see a few thunderstorms as well, with the highest chances (20-30%) south of roughly I-72/Danville where the LREF gives a 10-25% chance for more than 250 J/kg MUCAPE Saturday night. Most guidance then pushes an open wave through the area, while the deterministic 05.06.00z GFS and a handful of LREF members form a surface low. With the open wave solution, temperatures will remain near or slightly below normal in the wake of the front on Sunday, while the deepening surface low solution would give us quite the push of cool advection. The GFS, for example, keeps temperatures in the 40s much of the day Sunday beneath a deformation band of rain; fortunately, this is an outlier with NBM mean bringing afternoon temps into the mid 60s to low 70s, but it's something that we'll need to monitor in case forecast changes need to be made for Mother's Day.

We should get a moment's repose from the precipitation late Sunday through Monday, but then global deterministic models suggest the active pattern resumes with one/more shortwaves gliding east- southeast across the Midwest mid to late next week, sparking renewed shower and storm chances. The general trend is upward in temperatures, but given our position along the northeast edge of a ridge across the Great Plains, we remain near/in the storm track where precipitation and fronts will affect daily temperatures.

AVIATION /06Z TAFS THROUGH 06Z THURSDAY/

Issued at 1235 AM CDT Wed May 6 2026

VFR conditions will prevail at all TAF sites next 24hrs. Broken to mid clouds will remain blanketed over the sites through the night and tomorrow afternoon. Then clearing/scattering out of the clouds will occur Wed evening. Winds will be light to start but then become northwest during the afternoon with speeds of 7-10kts. Northwest winds will become lighter during the evening.

ILX WATCHES/WARNINGS/ADVISORIES

None.