As the Midwest enjoys a taste of spring, another threat is possible for this afternoon—severe weather.
As a major late winter/early spring storm moves through Iowa toward Wisconsin, a warm front has lifted northward through Illinois and southern Wisconsin. The combination of southerly winds and some sunshine has caused temperatures to climb into the upper 50s and 60s.
As a cold front lifts northeastward through northern Illinois into southern Wisconsin, a narrow line of thunderstorms is developing along the front. Southerly winds near the ground and westerly winds aloft create wind shear, which can cause thunderstorms to rapidly intensify, possibly to severe levels. The strong wind shear can also cause thunderstorms to rotate. This concentrates much of the energy into the updraft of winds fueling the storm, and can also lead to a possibility of tornadoes.
A few severe thunderstorms have made their way into southern Wisconsin this afternoon as well. Pea sized hail and wind gusts near 50 mph have been reported across Rock and Jefferson counties. The best chances for any additional severe weather will be through mid-afternoon, mainly for southeastern Wisconsin east of a Janesville to Waukesha line.
The threat for severe weather will end with the passage of the cold front. Much colder weather will arrive for Friday, with high temperatures about 20 degrees colder than today.
The fast movement of any thunderstorms this afternoon should limit the potential for heavy rain; however, as the snow and ice over southern Wisconsin continue to melt, any additional rainfall could lead to localized flooding. A Flood Watch is in effect for southern Wisconsin until 7 AM Friday morning.