MADISON, Wis. - After a night of severe thunderstorms and tornadoes, more severe weather is possible over southern Wisconsin later Tuesday, Wednesday, and possibly on Thursday as well.
The basic weather setup is unchanged over the central Midwest, according to News 3 meteorologist Gary Cannalte. Very warm and humid air is located just south and west of Wisconsin. In this type of an air mass, severe thunderstorms can develop very rapidly. But the presence of a layer of warm air aloft effectively keeps storms from developing, just like keeping a lid on a pot can prevent it from boiling.
Cannalte said southern Wisconsin is a little cooler as Monday night's storms stabilized the atmosphere a little, at least for now. However, the boundary that separates the very unstable air in Iowa and Illinois from southern Wisconsin is a stationary front that early Tuesday afternoon extends from southern Lake Michigan near Chicago back to near Cedar Rapids, Iowa, and farther to the northwest into eastern South Dakota. During the afternoon, the front may move northward as a warm front into northeastern Iowa and southern Wisconsin.
The position of this front is critical as to where severe thunderstorms might develop, and as to what type of severe weather is expected. As slightly cooler air aloft arrives later Tuesday afternoon over southern Minnesota and northern Iowa, the lid is taken off of the pot, so to speak, and thunderstorms should erupt rapidly in that area. Winds near the front can provide additional lift to the rising air currents to increase the intensity of the thunderstorms. Eventually, more thunderstorms might develop eastward along the warm front, and the storms in Iowa should head in our direction.
Because of favorable wind shear, which is the change of wind speed and/or direction, with height in the air over the Midwest, thunderstorms that develop can have rotating updrafts. In addition to possibly leading to tornado development, these rotating updrafts can send rain well into the top levels of the thunderstorm where temperatures are very cold. This can result in large hail, perhaps the size of golf ball or larger in some areas. Eventually, as falling rain and hail cool the air, the outrushing colder air can result in damaging straight-line winds with time as the thunderstorms consolidate into a large cluster.
Total rainfall for the week will range from 3 to 5 inches with locally higher amounts possible.
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