textproduct: Central Illinois

KEY MESSAGES

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

- After a couple more mild days, a preview of summer will arrive by early next week as highs soar well into the 80s by Sunday and Monday.

DISCUSSION

Issued at 254 PM CDT Thu May 14 2026

*** A Few Storms Late Tonight into Friday Morning ***

19z/2pm water vapor imagery shows a short-wave trough extending from southern Saskatchewan southward to Colorado. As this feature tracks eastward and interacts with a 45-55kt 850mb nocturnal jet, a cluster of showers and thunderstorms will form across southern Iowa/northern Missouri toward midnight. 12z CAMs have trended a bit slower and slightly further south with the track of the cluster...keeping the bulk of the activity south of the I-74 corridor. In addition, instability parameters are weaker than previously forecast, as evidenced by NAM MUCAPEs of only 100-300J/kg along/southwest of a Rushville to Springfield line by 12z/7am Friday. Have updated PoPs to keep conditions dry this evening, followed by categorical (80+) PoPs along/south of a Macomb to Lincoln line after midnight. Think it will mostly be showers with an occasional rumble of thunder and little to no risk for severe weather. The showers/thunder will spread further E/SE across the remainder of the KILX CWA early Friday morning before rapidly diminishing prior to midday. After that, a stray shower may remain possible along/south of the I-70 corridor through the afternoon...with dry conditions expected further north.

*** Additional Thunderstorms Friday Night into Saturday ***

After a lull in precip chances Friday afternoon and evening, the nocturnal low-level jet will once again provide the necessary forcing for scattered convective development late Friday night. MUCAPEs will be considerably higher than tonight in the 1000-1500J/kg range: however, deep layer shear will remain weak at just 25-35kt. As a result, think a few of the stronger cells may be capable of producing gusty winds and small hail: however, the overall severe risk will remain low.

As has been seen by the past few model cycles, it appears a better chance for strong to potentially severe thunderstorms will materialize by Saturday afternoon and evening as richer Gulf moisture arrives and a frontal boundary remains draped across north-central Illinois. Thanks to surface dewpoints climbing into the middle 60s, SBCAPEs will reach 2000-3000J/kg by peak heating. The main mitigating factor for widespread severe will again be the weak shear, with 0-6km bulk shear of only 20-25kt. Areal coverage of storms will peak in the afternoon and evening and think a few of the stronger cells could produce marginally severe wind/hail. The latest Day 3 Outlook from SPC highlights all of central/southeast Illinois with a Marginal Risk (level 1 of 5) accordingly.

*** Continued Stormy Early Next Week ***

As a short-wave trough crosses the Rockies, downstream ridging will help shove the frontal boundary back northward on Sunday...leading to a very warm and dry day across central Illinois with highs well into the 80s. The big question then becomes how quickly the western trough and its associated cold front can arrive. The 12z May 14 model suite has slowed the system...with the GFS showing FROPA Tuesday morning and the ECMWF Tuesday evening. This still looks like a situation where significant convection will fire along the front well to the west across Minnesota/Iowa/Kansas Monday afternoon...then push eastward into at least west-central Illinois during the evening. As a result, SPC continues to focus 15-30% probabilities for severe along/west of I-55. With the front slowing, confidence is growing that convection will re-develop across part of the CWA on Tuesday as well. The latest Day 6 SPC Outlook shows a 15-30% chance for severe across all of central Illinois on Tuesday, but think this may be a bit too generous and prefer to focus the highest severe chances mainly east of I-55 Tuesday afternoon and evening. Stay tuned to later forecasts for additional details. On a side note, we may need to watch out for blowing dust on Monday as strong S/SW winds gusting 30-40mph develop well ahead of the approaching cold front. After a breezy warm day on Sunday to dry the topsoil, even stronger winds may loft the soil if showers/storms are delayed until evening.

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

Issued at 1251 PM CDT Thu May 14 2026

Primary aviation forecast challenge will be timing potential convection later tonight into Friday morning. Latest models have continued to trend slightly further south with the track of an overnight storm cluster...with most solutions keeping the bulk of the activity south of the I-74 corridor. With minimal instability and a further south track, think the potential for thunder at KPIA/KBMI/KCMI will remain low. As a result, went with predominant showers with a PROB30 for thunder at those sites. Further south, have gone with TEMPO thunder at both KSPI and KDEC between 08z and 13z. The showers will shift east of the terminals and gradually dissipate by mid-morning. Winds will initially be light/variable this afternoon, then will become S/SE tonight into Friday morning. Winds will increase to greater than 10kt tonight, then will gust 20-25kt Friday morning.

ILX WATCHES/WARNINGS/ADVISORIES

None.