textproduct: Central Illinois

KEY MESSAGES

- Periods of showers and storms will continue into Saturday. A half inch to 1.5 inches of rain has already fallen, and there is a 60-80% chance for an additional inch or more. This will benefit the ongoing drought conditions, though there is a low chance for localized nuisance flooding with training storms this morning.

- There is a level 2 of 5 (slight) risk for severe weather tomorrow. The primary threat will be scattered damaging winds up to 70 mph, with a lower risk for tornadoes and hail up to the size of golfballs. There is at least a low chance for more severe weather late Friday into Saturday.

- Outside of storms, there is a 40-50% chance that south winds gust over 45 mph tomorrow. This could cause difficult driving conditions for high profile vehicles and blow around unsecured, lightweight objects.

- There is a 15-30% chance for freezing temperatures Saturday night and 30-50% chance Sunday night north of roughly I-70. Action may be needed to protect newly-emerged, tender vegetation.

DISCUSSION

Issued at 216 AM CDT Wed Apr 1 2026

***** SHOWERS, STORMS CONTINUE THIS MORNING, MORE TONIGHT *****

At 2am, numerous showers and thunderstorms were rolling across central Illinois as the nose of a 40-45kt LLJ is interacting with a cold front - resulting in 300-500 m^2/s^2 0-3km SRH, per our VAD profiler. While SPC's mesoanalysis currently depicts 500-1000 J/kg MUCAPE rooted around 850mb, which has allowed a few feistier storms to produce small hail, this should gradually wane throughout the early morning hours. As a result, storm vigor (rain rates, lightning) should decrease, though training cells will still be efficient rain producers. MRMS indicates most locations have seen a quarter inch or more over the past 3 hours, with pockets of over 1.5 inches where there was training of heavier storms; HREF suggests a 20-50% chance for an additional half inch or more of rain, with the highest chances north of roughly I-72, through 9am. Can't rule out some localized, nuisance flooding, but given the ongoing drought conditions this rain should be primarily beneficial.

We should get a short break in rain activity for areas north of roughly I-70 late this morning into early afternoon before scattered additional showers and storms develop ahead of another subtle wave after around 3pm. These will lift northeast across our area along and ahead of the warm front, which should reach I-74 by around 6am tomorrow. In the meantime, it'll be chilly with temperatures in the 40s and east winds around 15-20 mph north of the boundary. In addition, there may be a wave of fog along the front, potentially impacting commuters near the I-74 corridor Thursday morning, though CAMs suggest this will be brief (1-2 hours) in any given location.

***** WARM AND WINDY WITH MORE STORMS THURSDAY *****

Deterministic models and their respective ensembles agree that a surface low will develop beneath an increasingly negatively-tilted upper level trough lifting from the Plains into the Upper Midwest, bringing renewed warm and moisture advection to the Prairie State tomorrow. HREF mean surface dewpoints climb solidly into the 60s by afternoon, when a remnant ouflow from nocturnal storms will serve as a focus for more convection. With most of our effective wind shear (30-35 kt) focused in the lowest kilometer and low (<500m) LCLs, it wouldn't be surprising if we saw a tornado or two with any discrete cells or bowing line segments. In addition, mid level lapse rates will be steepening later in the day, especially west of I-55, favoring a risk for severe hail (again primarily with discrete cells). The main concern, however, will be damaging wind gusts with bowing multicell clusters due to a combination of unseasonably high PWATs over 1.5 inches (precip loading), inverted V soundings (dry sub-cloud layer), and strong winds aloft (approaching 50 kt at 900mb). Lots of uncertainty remains in the evolution of these storms due to model differences in location of ongoing convection (or remnant outflows) during the morning, though the HRRR/RRFS are advertising potentially more than one wave of strong/severe storms. SPC's level 2 of 5 (slight) risk seems reasonable given this uncertainty.

Outside of storms, tomorrow will be a windy day given the strong pressure gradient between the compact surface low to our west and high pressure over the Ohio Valley. Depending on the model you look at, forecast soundings in Bufkit for 10am to 8pm tomorrow indicate mean PBL winds between 25 and 35 kt, with top of channel winds ranging from 35 to 50 kt. This suggests significant uncertainty between the models in surface wind speeds driven by model differences in mixing depth. On the lower end of plausible scenarios, southerly gusts would top out at 35 to 40 mph, while the higher end magnitude (deeper mixing) could allow sustained winds to approach those values with gusts to 55 mph. Right now, LREF/NBM/HREF chances are nearly 50/50 on whether or not we'll need a Wind Advisory (issued for sustained 30 mph or gusts 45+ mph). In any case, folks will want to secure lightweight, unanchored outdoor objects and those planning on driving high profile vehicles (especially on west-east roadways) will want to keep a firm grip on the wheel. On the bright side (for those who like it warm), this strong warm advection will bring afternoon high temperatures solidly into the 70s.

***** MORE SEVERE STORMS FRIDAY INTO SATURDAY? *****

With the surface low pulling off to the north Thursday night, the cold front will decay as it approaches our CWA before lifting back north as a warm front ahead of the next system on Friday. Surface dewpoints will climb quickly back into the mid (locally upper) 60s, resulting in 1000-2500 J/kg MLCAPE (highest west) by mid-late afternoon. While soundings show a capping inversion and deterministic models depict no evidence of a forcing mechanism, we'll have to keep an eye out for any trigger during the afternoon as the environment could support severe weather. The higher chances will arrive Friday night into Saturday when the better forcing arrives along/ahead of the cold front. If a mature squall line develops upstream (as the RRFS suggests), strong deep layer shear may keep it going to result in at least isolated severe winds across our area even overnight. Additional storms may fire Saturday morning along the front mainly east of I-55, depending on what happens overnight Friday night. We'll continue to monitor model trends as the event gets closer.

***** COOLER WEATHER RETURNS SATURDAY *****

Behind the front, conditions will turn sharply cooler on Saturday with temperatures falling into the 40s by evening. Both Saturday and Sunday nights will bear watching for freezing temperatures which could damage newly emerged, tender vegetation. NBM gives a 15-30% for a freeze Saturday night and 30-50% chance Sunday night north of I-70.

AVIATION /06Z TAFS THROUGH 06Z THURSDAY/

Issued at 1210 AM CDT Wed Apr 1 2026

A slow moving cold front will become stalled out over central IL the next 24 hours and be the focus for periods of showers and thunderstorms as multiple disturbances track along it. MVFR to IFR ceilings observed late tonight will continue to decrease, with widespread IFR expected at all terminals by 09-12Z. Probabilities are high (70-80%) for ceilings to remain below 1k feet through the end of the TAF period. Northeast winds will veer to the east by afternoon with sustained speeds between 10-20 kts and gusts overnight up to 25 kt.

ILX WATCHES/WARNINGS/ADVISORIES

None.