On May 24, 2012, Wisconsin experienced its first significant outbreak of severe storms for the 2012 calendar year.
Time - early afternoon near Minnesota into the mid-evening hours in central Wisconsin.
Location - The activity occurred primarily over the northwest and central parts of the state, west-northwest of a line from Eagle River to Waupaca to Stevens Point/Plover to La Crosse.
Types of Severe Weather
1. Tornado - law enforcement confirmed one tornado spun up 2 miles south of Marathon City and move northeast for about 5 miles. This area is west-northwest of Rib Mountain State Park. Only tree damage. No structural damage, no injuries, no fatalities. No information on strength of tornado (EF-Scale rating). To view a picture of this tornado, read this story generated by the NWS Green Bay office here. Tornado warnings were issued for the counties of Marathon, Lincoln, and Langlade.
2. Wind Damage - straight-line downburst winds gusting to 60 to perhaps 75 mph knocked down trees or branches that brought down power lines. A radio tower (WBIZ) in Eau Claire collapsed about 430 pm. Trees on houses in or near Chippewa Falls. Worst of damage reports came from counties of Eau Claire and Chippewa. Other counties with wind damage report (trees) include Dunn, Trempealeau, Jackson, Taylor, Marathon, Vilas, Waupaca, and Portage. Other counties in northeast Wisconsin will probably have wind damage reports coming in between 9 pm and midnight. Emergency Management reports indicated about 12,000 customers lost electrical power due the storms.
3. Hail - one hail report (1-inch diameter) from Taylor Count. No damage reported. There may have been other storms wiht similar-sized hail but no reports were relayed to the National Weather Service.
4. Flooding - Over 2 inches of rain fell between 7 am Thursday and 7 am Friday, May 25th in some locations in the counties of Douglas, Bayfield, Ashland, Washburn, and Sawyer. Emergency Managers reported a couple roads were closed in Douglas County. Two-day rainfall amounts (May 23rd & 24th) reached 3 to 3.5 inches in isolated spots in northwest Wisconsin.
Reason for Severe Weather - a 75 to 100-mile-wide band of thunderstorms along and just ahead of a cold front moved east across Wiscosnin during the afternoon and evening hours as a strong low pressure moved northeast along the front from the Twin Cities area to Upper Michigan. Strong wind shear allowed for the development of severe storms. However, stronger atmospheric dynamics was restricted to the northern half of Wisconsin. Therefore, south of a line from La Crosse to Oshkosh the storms were weaker and below severe weather limits.
Storm Movement - individual severe storms moved quickly northeast at 60 to 65 mph while the band of storms moved east.
Map of Locations of Severe Weather Reports - the Storm Prediction Center in Norman, OK, produces an automated plot of all preliminary storm reports on a daily basis. These plots are found here. Below is the map for May 24, 2012. Click on image for larger version.
Maps of Rainfall Amounts - the northwest third of Wisconsin had generally over an inch of rain between 7 am Thursday and 7 am Friday, May 25th. Some locations had over 2 inches. Below are two rainfall maps. The one on the left is a plot of observed rainfall amounts and the one on the right is an automated contour plot. Click on the images for larger versions.
Additional detailed summaries of the storms can be found on the web sites of other NWS Forecast Offices that service Wisconsin:
Kapela, WFO Milwaukee