(11:45AM – Thursday, May 15th, 2025) Thursday midday update on storm system and a few main disturbances move through the region, which will bring a couple of rounds of rain and t’storm activity to the state, from this afternoon through Friday night. Severe t’storms will be likely with some of this activity, with significant severe weather expected.
Timing & Location…
•Thursday Afternoon – Friday Morning, May 15-16th: Much of Illinois.
•Friday Morning – Friday Night, May 16th: Large portion of Illinois.
Impacts…
•A level 1 to 4 severe t’storm threat is in place across much of Illinois today and tonight, for the likelihood of isolated to numerous severe t’storms. Environmental conditions will be supportive of the possibility of occurrences of strong tornadoes, damaging winds 75MPH+, corridors of widespread/significant wind damage, and hail larger than 2.00”.
•A level 1 to 3 severe t’storm threat is in place across a large portion of Illinois on Friday and Friday night, for the likelihood of isolated to scattered severe t’storms. Environmental conditions will be supportive of the possibility of occurrences of strong tornadoes, damaging winds 75MPH+, corridors of widespread/significant wind damage, and hail larger than 2.00”.
Update…
•With this update, we have slightly expanded level 2 and level 3 severe t’storm probabilities across portions of the state, as weather guidance continues to come into full agreement on higher coverage severe t’storm potential and confidence in this outcomes grows. We have also introduced a level 4 severe t’storm threat area across portions of Northeastern Illinois, as the highest coverage severe t’storm potential is likely across this corridor.
•With this update, little change was needed on the severe t’storm forecast for Friday and Friday night, as the going forecast is on track.
Discussion…
•Thursday Afternoon – Friday Morning, May 15-16th: As a strengthening storm system lifts through the Midwest, an arcing cold front will sweep northeastward across Minnesota, Iowa, and Wisconsin. Further south, a dry line will also sweep eastward, from Iowa and Missouri, quickly into and across Illinois. By mid to late this afternoon, as the cap is projected to erode/weaken, showers and t’storms will develop along the advancing dryline moving across the state. While the threat area across the state today is quite large, the greatest coverage and severity of activity will likely be across portions Northeastern and East-Central Illinois. Environmental conditions will be favorable for a severe t’storm threat should this scenario come to reality, including the threat for all modes of severe weather and occurrences of significant severe weather.
•Friday Morning – Friday Night, May 16th: Specific information regarding Friday’s severe t’storm threat will be provided in future updates.
