Tens of thousands of trees were broken, uprooted or downed across several counties, with Polk and Barron Counties being hit the hardest. Many outbuildings were destroyed by wind, along with roofs off barns and sheds. The vast majority of damage was due to a derecho that started over east central Minnesota, and progressed southeast across Wisconsin, and into lower parts of Michigan. The path length was nearly 490 miles long. Three tornadoes also produced damage, but areal extent of the tornadoes paled in comparison to the damage caused by the downbursts.
During the late morning, and early afternoon of Friday, July 19th, a surface low moved from northeast South Dakota, eastward across central Minnesota, and into west central Wisconsin by the evening. There was a tight thermal gradient along the surface low/warm front across central Minnesota. During the afternoon, dew points rose to near 80 in the warm sector, with 50s/60s north of the front. This contrast produced MLCAPEs of near 5000 J/kg south of the front boundary. Effective wind shear parameters were very strong with values of 50-70 knots across central Minnesota, and into west central Wisconsin by the late afternoon. This environment allowed for supercells to form which congealed into a bow echo that raced across east central Minnesota, and into west central Wisconsin. Very large hail, damaging straight-line winds, and a few tornadoes occurred with this large bow echo.
Based on a collection of video, pictures, and collaboration of local law enforcement offices, and emergency managers, there were thousands of trees uprooted or blown down in a swath that went from Polk County, southeast across Barron, Dunn, Chippewa and parts of Rusk Counties. Embedded in the straight-line wind damage, a few tornadoes occurred.
The first tornado occurred east of Balsam Lake, and tracked east to north of Turtle Lake where it crossed into Barron County. The tornado continued into Barron County before dissipating east of Turtle Lake. This tornado was rated EF1 that was on the ground for nearly 14 miles. A weaker tornado occurred east of Fox Creek and was only on the ground for a minute with a path length of around 1 mile.
The county of Chippewa indicated that most of the damage was from the Village of New Auburn in the northwest to Otter Lake in the east.