textproduct: Central Illinois

KEY MESSAGES

- Periodic storm chances will persist through early next week...with the greatest probability for convection focusing tomorrow...then again late Monday into Tuesday.

- Windy and very warm conditions are expected by Sunday and Monday as highs surge well into the 80s.

DISCUSSION

Issued at 211 PM CDT Fri May 15 2026

*** A Few Thunderstorms Late Tonight into Saturday ***

Short-wave ridging in the wake of the morning MCS has led to mostly sunny skies across much of central Illinois early this afternoon...with 18z/1pm satellite imagery showing the only lingering cloud cover near the Indiana border. Mostly clear and dry conditions are expected to continue through this evening before the low-level jet interacts with an approaching cold front to trigger scattered showers and thunderstorms late tonight into Saturday morning. The 12z May 15 NAM shows a 40-45kt 850mb jet developing from Texas northeastward to Iowa after dark. Thunderstorms will initially develop along/ahead of the cold front across portions of Wisconsin and Iowa this evening, but these will tend to track northeastward and diminish across the southern Great Lakes late tonight as they outrun the jet. Meanwhile further S/SW, most CAMs indicate scattered convection forming within the jet and just south of the cold front across northern/central Missouri between 06z and 09z. This is the activity we will initially have to keep an eye on as it tracks eastward across mainly the southern half of the KILX CWA toward dawn Saturday. With MUCAPEs of 1500-2000J/kg, the storms will be able to maintain themselves as they push eastward: however, weak 0-6km bulk shear of just 20-30kt will prevent significant severe weather overnight. A few of the strongest cells may be capable of producing gusty winds/small hail along/southwest of a Macomb to Mattoon line late tonight through mid-morning Saturday.

Once the initial round of showers dissipates and/or exits into Indiana, the big question will be whether convection will be able to re-develop Saturday afternoon. While deep-layer shear will increase into the 30-40kt range, extensive cloud cover early in the day will tend to suppress temperatures and instability. The 12z HREF indicates mean SBCAPEs of just 500-1000J/kg by peak heating. Several of the CAMs are skimpy on precip during the afternoon...with both the HRRR and RRFS suggesting development much further south across southern Illinois into the Ohio River Valley where instability will be greatest. This scenario of course depends upon what happens tonight. If the storm clusters develop across Missouri and track eastward across central Illinois Saturday morning as expected, then the severe risk for the afternoon will remain low. The current Day 2 SPC Convective Outlook features a Marginal Risk (level 1 of 5) for severe weather on Saturday, and this seems reasonable based on the latest thinking.

*** Stormy Weather Early Next Week ***

The cold front that will be approaching Illinois late tonight will stall across the region on Saturday, then lift back northward as a warm front Saturday night in response to developing mid-level ridging. All models show central Illinois firmly in the warm sector on Sunday, as S/SW winds gusting 25-30mph push afternoon highs into the middle to upper 80s. Things get more interesting during the Monday/Tuesday time period as a significant trough and its associated cold front come into the picture. The 12z May 15 models are in much better agreement concerning the timing of this process...with both the GFS and ECMWF showing FROPA Tuesday afternoon/evening. Given this trend, confidence is growing that significant rain/storm chances will likely hold off until Monday night. While the current forecast features likely PoPs Monday afternoon, think these will eventually be lowered...as the primary focus for widespread storms will initially be much further west across eastern Kansas/western Missouri immediately ahead of the front. This convection will eventually spill into the Illinois River Valley by mid to late evening, posing a damaging wind/hail risk. The storms will likely decrease in intensity overnight as they push eastward across the I-55 corridor. The most recent SPC outlook still highlights areas along/west of I-55 with a 15-30% chance for severe.

With a slower FROPA expected, the likelihood of convective re-development across parts of central Illinois on Tuesday continues to grow. While it is still too early to pinpoint the exact development zone, most models and conventional wisdom suggests it will be along/east of I-55. SPC continues to show a 15-30% chance for severe across the entire KILX CWA, and this seems reasonable until minor timing discrepancies and mesoscale details are better resolved.

*** Blowing Dust Potential ***

With planting season in full swing and crops only just beginning to emerge, there is plenty of bare soil to be blown about if the proper conditions are met. Despite the expected rainfall late tonight and Saturday, a warm and windy day on Sunday will help dry the immediate topsoil. If showers/storms do not form within the warm sector well ahead of the approaching cold front, there is growing concern that S/SW winds gusting 30-40mph will lead to additional drying and perhaps areas of blowing dust where active plowing is occurring on Monday.

AVIATION /00Z TAFS THROUGH 00Z SUNDAY/

Issued at 605 PM CDT Fri May 15 2026

Thunderstorms are expected to expand in coverage from Wisconsin into Kansas this evening and slowly shift east overnight into Saturday morning. Showers and storms will move across the central Illinois terminals through the morning, and while there remains some uncertainty on precise timing within a couple hours, the best favored time is between 09Z-16Z. Precip is expected to settle over southern Illinois Saturday afternoon and evening. Outside of the influence of storms, south to southwest winds and VFR conditions are expected to prevail through the period. A brief window of IFR is possible within storms, and cannot rule out a gust front near the leading edge of storms that turns winds NW/N for a couple hours.

ILX WATCHES/WARNINGS/ADVISORIES

None.