On the morning of May 2nd most of the southern half of the SkyWarn 13 viewing area found themselves under a slight risk for severe weather. Temperatures surged in the afternoon into the low 80s in both Eau Claire, La Crosse, and surrounding areas. As the 7pm surface map below shows there was a stationary front from central Minnesota into northern Wisconsin.
There was another boundary at play that set up in the afternoon. Storms fired in southern Minnesota taking advantage of high instability, shear, and a warm moist flow from the south. Central Minnesota had lower dew points in the 50s and that same set up occurred in Western Wisconsin. Here at 7pm, you can see La Crosse with dew points in the 60s and dew points 10 degrees lower up in Eau Claire. The storms would ride that line into Buffalo Co. into the evening hours.
The storm really picked up in intensity has it moved into Western Wisconsin. A tornado warning was issued for parts of Buffalo Co. when a strong rotation signature showed up on radar moving through Alma, Cream, and Waumandee. The radar loop goes from 9:15pm to 10:45pm.
This complex used to be mainly a lone supercell that tracked through southern Minnesota. Just before the Buffalo Co. tornado warning another cell had merged quickly into that supercell. That's when this complex would produce very strong winds has it moved through Buffalo and Trempealeau Counties. There would of course also be all the hail. Most pictures I've seen showed the hail was up to golf ball size...maybe a bit higher in spots. You can see the strongest reflectivity in the radar image above like the purples and pinks form a bow as it goes through eastern Buffalo Co. and through towns like Arcadia, Whitehall, and then eventually to Blair.
Here are storm reports on a map from the La Crosse National Weather Service. It was determined all the damage was due to straight line winds. After seeing the damage first hand in Blair I completely agree.
The wind and hail damage was extensive through Buffalo and Trempealeau Counties. Blair was hardest hit. It was incredible to see the damage down there though. Pretty much every home was impacted somehow by the storm. You can see a whole series of stories done by Jenny You, Kevin Hurd, and myself. There's plenty of video there you can get from the link below.
Here are some images from Blair.
Winds in the Blair area were estimated between 70 to 80 mph. The first image below is from damage in Buffalo County with the second being from Whitehall.
This storm also produced a lot of lightning. It's was reported that lightning was responsible for a fire at the home of Congressman Ron Kind. Here's a great pic from a viewer in Mondovi. It was quite lightning show!
This complex of storms moved fairly slow between 25 to 30 mph and was dumping impressive rainfall amounts at a very high rate. In Blair, the rain came down so heavy that a big stretch of Highway 95 was covered in water just outside the farmstead where that barn collapsed above. There were also a lot of trees down on the highway as well. Here are some of the highest rainfall reports.
New Lisbon 2.08"
Black River Falls 1.64"