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Severe weather hits parts of Wisconsin on Sunday with tornadoes and large hail. Through Sunday evening the storms missed southeast Wisconsin. While storms are possible along the cold front through about midnight, the threat for severe weather is now lower in the southeast part of the state.
To check out any storms and to track them, just click on the interactive radar below.
Before we talk about why the storms avoided southeast Wisconsin through early Sunday evening, let’s look at the storms around the state.
First, a supercell thunderstorm near La Crosse produced hail larger than golf balls at St. Joseph’s Ridge School. This picture is courtesy of Jodi Roesler and was taken around 5:00pm Sunday.
Another aspect of the severe weather was tornadoes. Numerous tornadoes were reported in western, central and northern Wisconsin on Sunday. A way to detect tornadoes is by using radar. Below is the velocity image at 6:23pm on Sunday. The red and green color right next to each other in Adams county indicated strong rotation. At this time there was a tornado reported near Cottonville, WI.
We’ll get a final tornado count across the state on either Monday or Tuesday and pass that along in the blog.
As a cold front nears southeast Wisconsin late Sunday evening, some thunderstorms are possible. The threat will transition more to hail and wind versus tornadoes. The main tornado threat should stay well north of Milwaukee and also well south. If anything does pop up we’ll be here to let you know.
Through Sunday evening, the reason that storms did not fire in southeast Wisconsin was the lack of a trigger. A ‘cap’ was in place. Here is a great explanation of a capping inversion. Later Sunday evening a cold front should erode the cap allowing some storms to form.
A layer of relatively warm air aloft (usually several thousand feet above the ground) which suppresses or delays the development of thunderstorms. Air parcels rising into this layer become cooler than the surrounding air, which inhibits their ability to rise further. As such, the cap often prevents or delays thunderstorm development even in the presence of extreme instability. However if the cap is removed or weakened, then explosive thunderstorm development can occur.
The cap is an important ingredient in most severe thunderstorm episodes, as it serves to separate warm, moist air below and cooler, drier air above. With the cap in place, air below it can continue to warm and/or moisten, thus increasing the amount of potential instability. Or, air above it can cool, which also increases potential instability. But without a cap, either process (warming/moistening at low levels or cooling aloft) results in a faster release of available instability – often before instability levels become large enough to support severe weather development.
The best way to detect a cap is by looking at sounding data and skew-T diagrams. I’ll try to post a sounding with Sunday’s cap later on. For now we will continue to watch for the possibility of any storms pushing into southeast Wisconsin. But clearly the best chance for severe weather is over central and northern Wisconsin, and farther south into Illinois.