EF1 tornado in Todd County, Minnesota

Hundreds of trees were uprooted or broken. Several outbuildings lost roofs. The damage pattern in this part of Todd County was very complicated, but ground and aerial surveys revealed a tornado moved through part of Clarissa. Maximum winds were estimated at 90 mph.

A line of severe thunderstorms that developed across South Dakota and Nebraska during the afternoon of Thursday, May 12th, was a classic bow echo that surged north and east across western Minnesota.

Temperatures in the mid to upper 90s along with dew points in the mid to upper 60s created ample instability for thunderstorms to develop ahead of a cold front, once the cap weakened during the evening. Despite fairly muggy dew points, the hot surface temperatures created inverted-V soundings that were primed for damaging wind potential. Thunderstorms came in three waves during the evening, as marginal shear values prohibited any long-lived or well-organized thunderstorms across the area.

Winds were measured by wind sensors at over 100 mph across portions of South Dakota, with a measured wind gust at Madison, Minnesota of 94 mph. There were also numerous measured wind gusts between 60 and 80 mph across west central and southwest Minnesota with embedded surges that produced a few tornadoes. The most concentrated area of damage based on reports of farm equipment, trailers, semis, trees, power lines, and other debris, occurred near the upper Minnesota River Valley, northward to Alexandria and Long Prairie.

Over Stevens County alone, structural damage was considerable as the majority of the damage was to farm outbuildings, sheds and grain bins. There were a few locations in the county where the main inhabited house or home structure did suffer loss of roof and siding and windows but those were more isolated in nature. Many locations had debris tossed a mile northeast from its parent location. Nearly 100% of the damage witnessed in Stevens county was consistent with a straight line wind event, with just one tornado crossing the southeast corner of the county.

Ten tornadoes were confirmed this day, with two in Lac Qui Parle County, including a house in Bellingham that had much of its roof removed. In northwestern Swift County, a tornado tipped over trailers and various farm equipment was heavily damaged. Two tornadoes were in Todd County, including one that moved through Clarissa. Two more were in Morrison County, and one was on the east side of Lake Alexander, where many trees came down on vehicles, sheds, and cabins. A tornado also occurred in Douglas County, on the northwest side of Alexandria, where EF2 damage was noted. The ninth tornado touched down south of Lowry in Pope County and was caught on video, and the tenth was in northwestern Stearns County, affecting the north side of Sauk Centre, and it was also caught on video.