170 mph winds: Deadly Otter Tail County tornado rated a rare EF-4

Wednesday’s devastating tornado in Grant and Otter Tail counties is the strongest to hit Minnesota in almost 10 years.

On Friday, the Grand Forks National Weather Service office storm survey rated Wednesday’s tornado a rare EF-4 with peak winds of 170 mph.

The tornado touched down in northern Grant County then quickly crossed into Otter Tail County where it did the majority of the damage. The tornado was on the ground for 31 minutes and cut a 9-mile path that was 650 yards wide at the widest point. That’s more than six-football-field wide.

Here are some key details from the storm survey.

Here is more granular detail from the Grand Forks NWS office.

Public Information Statement National Weather Service Grand Forks ND

1137 AM CDT Fri Jul 10 2020

NWS DAMAGE SURVEY FOR 07/08/20 TORNADO EVENT... .

OVERVIEW... A rapidly developing supercell thunderstorm produced a long lived and deadly tornado that originally touched down in far northern Grant County MN, as a weak tornado /EF0-EF1/, but then quickly intensified into a strong to violent tornado as it crossed into southern Otter Tail County, near MP70 on Interstate-94.

The tornado intensified as a strong tornado /EF2-EF3/ as it moved northeastward through southwestern St. Olaf Township and crossed Beebe Lake. It likely reached maximum EF3 intensity after it crossed Highway 82 and as it destroyed a machine shop and yard on the downwind side. It then continued in a northeast direction and reached both maximum width and intensity as it moved into and across a rural homestead along 120th Street and into Blacken Lake. The tornado continued in a northeast direction producing mainly tree and cropland damages as it crossed CR117, north of Kvam Church.

Video imagery and deep ground scour indicate that the tornado maintained its intensity as a strong to violent tornado even as it narrowed and eventually began to rope out, near 325th Avenue, between 145th street and CR12. The storm that produced this tornado continued eastward across southern Otter Tail County and may have produced one or more additional but brief tornadoes along its path.

Fatal moments

The tragic scene the storm survey team describes from the machine shed where one man died is chilling. It is hard to believe anyone could have survived a direct hit from a tornado this intense.

SURVEY SUMMARY: Of particular note, a well built machine shop of fairly new construction and was complete swept from its foundation and destroyed downwind, with one fatality and one injury there.

At one homestead, a well built two-story house was completely swept from its foundation and decimated in a widespread and distant debris field. Two injuries occurred here as a couple shelter in the basement and debris, including a vehicle, dropped into the exposed basement.

EF Scale: The Enhanced Fujita Scale Classifies Tornadoes into the following categories. EF0...Weak......65 to 85 mph EF1...Weak......86 to 110 mph EF2...Strong....111 to 135 mph EF3...Strong....136 to 165 mph EF4...Violent...166 To 200 mph EF5...Violent...>200 mph

This is the first EF-4 tornado in Minnesota in nearly 10 years.