Following a rare quiet period of weather across the Midwest as of late, the pattern is reloading and will offer several chances of severe weather from the Dakotas through the mid-Mississippi River Valley. The combination of late-spring heat and humidity, with sufficient wind shear, will set the table for a series of severe weather events with damaging hail, destructive winds and perhaps a few tornadoes.
Wednesday, the first day of the organized storm threat, we see high-end instability build across western Minnesota, northwest Iowa, and into South Dakota to Nebraska. The source of organized storm activity will be an upper-air disturbance coming from the northwest that will increase the wind shear across the area.
As a nearly-stationary boundary sits over the region, the combination of the instability and wind shear will generate the threat for severe weather.
Guidance suggests thunderstorms forming from southern Minnesota into northern Iowa, however it’s possible storm initiation will include areas farther west into South Dakota into northern Nebraska. These details will be ironed out as higher-resolution models get in range.
Thursday appears to be the day with the highest risk across the region with more widespread severe weather activity in the forecast. Moderate to high CAPE, or instability, will expand from Michigan west into Nebraska and Kansas. This instability will sit along and ahead of a slowly-moving cold front which will be the trigger for afternoon storms.
Models suggest widespread storm formation across this area of instability Thursday afternoon into the overnight hours.
Given the fact shear vectors will be more parallel to the cold front, this would mainly support a damaging wind threat with a lesser potential of large hail and tornadoes. With that said, any residual boundary from the Wednesday’s storms could create a localized area of tornado potential.
Above, you can see the bulk shear in the atmosphere. Notice the wind barbs area parallel to pink line, which is where the cold front is forecast to set up. Again, this would lead to a mainly damaging wind threat across Iowa, southern Wisconsin into northern Illinois.
The American GFS model in particular is pretty set on this idea of a higher-end wind threat in the region Thursday. Worth noting these particular events area rather difficult to pin down ahead of time, but it’s worth continuing to watch model trends in the coming days.
Keep an eye on the evolving forecast, especially those with travel or outdoor plans. We’re entering MCS season which is a classic wind and heavy rain threat across the corn belt.
-Meteorologist Nick Stewart