From the National Weather Service:
We will be closely monitoring the development and evolution of thunderstorms upstream across Iowa and Minnesota this morning and afternoon. These storms are then expected to roll into southern Wisconsin later today and tonight.
There remains a lot of uncertainty with how things will unfold, but the potential for strong to severe storms has increased considerably over the past 24 hours.
The main threat will be strong and damaging straight-line winds and possibly large hail. An isolated tornado can't be ruled out. We believe areas south and west of a line stretching from about Baraboo to Madison to Delavan have the higher chance for seeing severe weather. The risk will fall off to the north and east due to cooler and drier air in that region.
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Image: National Weather Service