The severe weather threat for the southern Illinois region has been upgraded ahead of expected afternoon storms.
“Ongoing thunderstorms this morning complicate the overall scenario to some extent, but a very favorable corridor for intense supercells and strong tornadoes is apparent this afternoon/evening across parts of Missouri into Illinois, where a Moderate Risk (Level 4 of 5) has been introduced,” the Storm Prediction Center said.
The main threat will be in the afternoon hours, those in the morning may be experiencing the first round of thunderstorms, with even some of these storms being severe. That isn’t the main concern. The main concern comes in the afternoon hours, particularly in the 2 p.m. to 10 p.m. timeframe, where stronger supercells are expected to form.
“If clouds clear more quickly, the environment will be favorable for higher-end severe thunderstorms including the maximum hazard intensities,” the St. Louis NWS said.
Currently, the St. Louis NWS highlighted the most likely timeframe to see severe weather in the St. Louis area into Central Illinois will be in the 4-8 p.m. timeframe, but they have cautioned that there is still uncertainty as to when due to the morning storms and how they affect the environment.
“Uncertainty remains in when severe thunderstorms will develop during the afternoon due to lingering effects of the morning thunderstorms and how the environment will react,” the St. Louis NWS said. “Once thunderstorms develop they are expected to progress east.”
A 15-29% tornado risk is in place across the southern Illinois region into the Mississippi Valley region. This 15% area stretches from the I-72 interstate south, just south of the Jacksonville area and covers the St. Louis area, including Alton and Edwardsville. The St. Louis area is directly in the center of the tornado risk.
There is a Cig-2 intensity risk for the region, which means there’s an increased risk of EF3+ tornadoes on the day.
“Supercells capable of very large hail and strong tornadoes are expected during the afternoon and early evening hours.”
An additional 10% risk of tornadoes stretches up to Bloomington and Peoria and as far south as the Arkansas state border.
Another question will be if these storms congeal into a line. If/when these storms congeal, the severe wind risk will be maximized. There is a 45% risk of severe wind across the state of Illinois.
“Later in the evening, storms will tend to transition into a mixed mode of supercells and line segments. Once this occurs, there could be a shift to damaging winds and (generally weaker) tornadoes. There is still uncertainty on where and how quickly this transition will occur during the evening.”
There is a 30% hail risk with this system as well with a Cig-1 intensity risk. This means there is an increased chance of 2.50+ inch hail.
The next severe weather outlook for the day will be released around 11:30 a.m. CDT. From there, more information on how the morning storms affect the environment will be in place and further updates will be provided.
