STRONG STORMS POSSIBLE THURSDAY & FRIDAY

MAY 14, 2025 -- Let's talk about the risk for severe storms coming up Thursday and Friday. Storm chances this time of year become very impactful with numerous graduations, parties, and other outdoor events often planned around school and family functions.

THURSDAY: At the time of this writing, the Storm Prediction Center has all of Southern Illinois in a Level 2 (out of 5) for Thursday afternoon and evening. Severe storm ingredients such as moisture, instability, and shear are all in place, but there remains a lot of uncertainty regarding storm development. The uncertainty is due to a "capping inversion". A capping inversion is a layer of warm air aloft that prevents cooler, moist air near the surface from rising, effectively "capping" the atmosphere. This can suppress storm development until the cap weakens or breaks, at which point explosive thunderstorm growth may occur. When the capping inversion is pronounced and holds, then storms may not develop at all.

Thursday is seen as a "boom or bust" type of scenario. There is a cold front approaching from the northwest later in the day, which could be enough to overcome the capping inversion. If this occurs, then we would likely end up with a few storms, but they could be severe with very large hail, strong winds, and potentially a tornado or two. Unfortunately, we probably will not know if the capping inversion will hold or not until tomorrow afternoon and evening.

As for potential timing on Thursday afternoon, if we see storms develop, it would primarily be after 3 p.m.

A cold front will sag to around the Ohio River overnight Thursday and into Friday. This front will then return north on Friday as a warm front, setting the stage for another day of severe storm potential.

FRIDAY: Friday brings a bigger threat, or at least higher confidence, for severe storms in Southern Illinois. The capping inversion is not nearly as pronounced, yet all of the severe storm ingredients are in place. As a result in high confidence, the Storm Prediction Center upgraded all of Southern Illinois to a Level 3 (out of 5) for Friday afternoon and evening.

There will be two areas to keep a close eye on for storm development on Friday. The warm front is expected to be draped somewhere between Benton and Salem. We could see some storm development towards the early part of the afternoon close or just to the south of this warm front. By mid-afternoon, another area of potential storm development will be focused just ahead of an approaching cold front moving into Southeast Missouri.

Winds aloft favor a mix of storm clusters and potentially a few supercells. With the environment in place, the threats will be very large hail, scattered damaging winds, and a few tornadoes.

There is still uncertainty regarding the exact placement of the strong storms and the exact timing for when they will move through the region. There are some indications that we could see a few storms developing as early as 1-2 p.m. We'll know more as we get closer. If you have plans to be out and about Friday afternoon and evening, I would encourage you to simply be paying attention to the weather.

SATURDAY: The front will settle south of the region to start the weekend. Saturday will be a DRY day in Southern Illinois.

SUNDAY & EARLY NEXT WEEK: The front will once again lift into the region by Sunday afternoon. Angled from west/northwest to east/southeast, this front will likely be the focus for storm clusters to develop. We could see some of these as early as Sunday afternoon with more potentially Monday and Tuesday.