textproduct: Central Illinois

KEY MESSAGES

- The stretch of warm weather is expected to last through Friday, with daily temperatures climbing near 80 degrees, and at times, the mid-80s. Breezy winds, occasionally reaching 25-35 mph, will accompany this warm period.

- This week will be riddled with thunderstorm potential. Today, Wednesday, and Friday currently exhibit the highest probability (15-30%) of severe weather.

- There is also potential for substantial accumulative rainfall throughout the week, with our multi-model ensemble predicting a medium (30-50%) chance of exceeding 2 inches through Saturday in areas north of Interstate 72.

DISCUSSION

Issued at 301 AM CDT Tue Apr 14 2026

Satellite imagery reveals two key areas of convection this morning. First, a cluster of decaying thunderstorms in central Missouri, as shown by warming cloud tops. The associated convectively-augmented shortwave is anticipated to move eastward along the I-70 corridor into central Illinois later this morning. Second, a persistent area of convection is situated further north over northeast Iowa and southern Wisconsin, near the primary surface boundary, with its outflow boundary slowly advancing southward into northern Illinois.

The region situated between these two features remains favorable for renewed thunderstorm development. A strong 40-50 kt low- level jet (LLJ) is present, maintaining a healthy sink of MUCAPE (1500-2000 J/kg). Furthermore, the eastward-tracking convectively-augmented shortwave is expected to boost effective layer shear to nearly 40 knots and sustain favorable mid-level lapse rates.

Given this combination of sufficient CAPE, shear, and residual forcing mechanisms, the re-ignition of convection into central and east-central Illinois is considered plausible this morning. Model guidance, specifically the HRRR and RRFS, suggests the potential development of an elevated thunderstorm cluster. If this materializes, the primary convective hazard through mid- morning will be hail.

Despite the development of a highly volatile atmosphere this afternoon, featuring surface temperatures in the mid-80s, 60s dewpoints, favorable mid-level lapse rates, an intensifying mid- level jet, and robust SBCAPE (2500-3500 J/kg), the potential for thunderstorms remains low. This is primarily due to a persistent cap, maintained by residual subsidence and marginal mid-level height increases following the morning shortwave. This cap, particularly in the 1-3 km layer, could significantly limit, or even prevent, convective development.

Synoptic forcing today appears nebulous, compounding the forecast difficulty: the main surface front is expected to stay north; the location of potential convective outflows is unknown; and no strong shortwave is lifting across the area. This has led to substantial uncertainty in the timing and location of storm initiation, with CAMs struggling to accurately predict storm evolution.

However, if updrafts manage to breach the cap later this afternoon or early evening, the environment is primed to support significant-severe convective hazards. The profile is a classic "loaded gun", but the trigger (forcing) is largely missing, or at least unknown at the moment.

Regardless of today's convective outcome, the likelihood of widespread convection increases significantly by Wednesday morning. This is expected as a low-level jet axis establishes across the region and a preceding shortwave disturbance ejects ahead of a more potent trough tracking across the lee of the Rockies.

Additional rounds of storms are then likely through Wednesday evening as the main trough swings across the Mid-Mississippi Valley. A favorable CAPE/shear environment is anticipated to support elevated supercell and multicell structures over central Illinois throughout the day, capable of producing all severe hazards, including localized heavy rainfall.

Thursday looks to be a region-wide break from storms due to synoptic-scale subsidence moving in behind the departing upper trough.

Thunderstorm activity is then expected to return over the weekend, specifically Friday night into Saturday. This is associated with a compact shortwave trough lifting across the Mid-Mississippi Valley ahead of a pivoting, more vigorous trough and its accompanying cold front. The CAPE/shear parameter space appears volatile enough to support an organized severe convective risk, even though the front appears to pass during a diurnally unfavorable time.

Following the cold frontal passage, temperatures will cool significantly from Saturday night through Monday as the warm, moist air mass from the previous week is flushed out. The latest NBM deterministic guidance supports Sunday afternoon high temperatures near 60 degrees, with overnight lows around 40 degrees.

AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 551 AM CDT Tue Apr 14 2026

Isolated thunderstorms are ongoing to start this TAF period, but will gradually diminish in coverage from west to east through 15z. Broken MVFR ceilings are currently observed upstream across northeast Missouri and southeast Iowa, and will likely overspread the KPIA- KBMI- KCMI terminals, with lower probabilities to the south. These are forecast to lift above 3 kft AGL by midday, with VFR conditions prevailing for the remainder of the TAF period.

An isolated storm cannot be ruled out this afternoon, but confidence and coverage remain too low to mention in the TAF at this time. The better chance for widespread thunderstorms arrives between 06z-12z, and we have introduced a PROB30 mention during this timeframe across all terminals.

Southwest winds will remain gusty through the period, near 25 kts at times.

CLIMATE

Issued at 307 AM CDT Tue Apr 14 2026

RECORD HIGHS FOR 4/14:

PEORIA: 86 (2024) SPRINGFIELD: 89 (2006) LINCOLN: 87 (2006) NORMAL: 84 (2006) URBANA: 84 (2010) DECATUR: 88 (1941)

FORECAST HIGHS FOR 4/14/2026:

PEORIA: 84 SPRINGFIELD: 87 LINCOLN: 86 NORMAL: 84 URBANA: 84 DECATUR: 85

ILX WATCHES/WARNINGS/ADVISORIES

None.