A destructive and unfortunately tragic day unfolded in Minnesota, as storms lashed western, central, and northern areas in the early morning, and again in the evening, with damaging winds, hail, and one lethal and particularly violent tornado. Heavy rains also accompanied the storms, with minor flooding reported in some areas.
The first round of intense storms developed in Montana on the evening of Tuesday July 7, with storms racing through North Dakota at 50-65 mph, and making it into western Minnesota around 3 AM on Wednesday the 8th. The storms had produced nearly continuous 65-85 mph wind gusts and damage in North Dakota, and continued doing so into west-central Minnesota. The Fergus Falls municipal airport in Otter Tail County reported a wind gust of 83 mph at 4:35 AM. Gusts of 74 and 71 mph were reported by road weather stations in Wilkin County. The winds bent wind turbine blades, flipped an irrigation unit, blew down trees and power lines, and overturned ten recreational vehicles at a private campground. Given the long track of damage and wind gusts well above severe levels (58 mph is the threshold for winds to be considered "severe"), it is likely that this event qualified as a derecho (pronounced "deh-ray-cho").
The wind damage dropped off right around sunrise, but the intense thunderstorms continued pressing southeastward, producing heavy rains and vivid lightning. Rainfall totals of 1.5 to 2.5 inches were common through Otter Tail, Douglas, Todd, and Stearns Counties. The storms weakened in eastern and southern Minnesota, and had dissipated entirely by around 11 AM.
As a sultry air mass sent Heat Index values soaring to over 100 degrees F across central and southern Minnesota in the afternoon, a new upper-air disturbance emerged from the Dakotas. The combination of intense heating, high humidity, and strong winds aloft led to explosive atmospheric conditions.
New thunderstorms erupted in western and central Minnesota during the late afternoon. These slow-moving, intense "supercell" thunderstorms remained relatively isolated at first, and often split into "left-moving" and "right-moving" pairs.
One of the first supercells of the day produced a confirmed tornado that tracked from Grant into Otter Tail County. Unfortunately, this large, widely-photographed tornado produced significant damage and killed a 30-year-old man near Dalton, while injuring two others. The Grand Forks office of the National Weather Service rated the tornado an EF4 on the Enhanced Fujita damage scale, corresponding to winds in excess of 165 mph. This is the first tornado fatality in Minnesota since 2011, and the first tornado rated EF3 or greater since August of 2010.
Tornadoes rated at EF4 (formerly F4 on the Fujita scale) are rare, and cause an unusual amount of damage, even to well-built structures. Minnesota has had just seven days since 1980 with F4 or EF4 tornadoes:
- July 3, 1983 (Andover)
- June 16, 1992 (Chandler and Lake Wilson)
- March 29, 1998 (Comfrey)
- July 25, 2000 (Granite Falls)
- June 17, 2010 (One near Almora and Bluffton, one in Wadena, one in Freeborn County)
- August 7, 2010 (Wilkin County)
- July 8, 2020 (Otter Tail County)
In addition to the tornadoes, the storms also produced large hail, torrential rains, and eventually, strong downburst winds. Some observers in Otter Tail, Hubbard, Wadena, Cass, Crow Wing, and Aitkin counties reported 3-5 separate instances of hail. The Park Rapids airport measured a wind gust of 75 mph, with power outages reported near Hackensack, Akeley, and Aitkin.
Along with multiple instances of severe weather, the thunderstorms also brought repeat rounds of heavy rainfall to many of the same areas. The National Weather Service cooperative observer north of Isle on the east side of Mille Lacs, reported 3.38 inches of rain. A nearby CoCoRaHS observer reported 3.70 inches. The rain produced localized flash-flooding near Brainerd and Aitkin, but also provided much-needed relief from persistently dry weather and drought. Areas where drought has been especially harsh in recent weeks, from the Brainerd Lakes area, to Cloquet and Duluth, saw 1.5 to 3 inches of rain.
Following is the text of the initial National Weather Service statement on the Otter Tail County tornado(es). This will be updated as new information becomes available.
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 UPDATE CORRECTION ON INJURIES. 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 /EF4/ 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. TORNADO GRANT AND OTTER TAIL COUNTY SOUTHEAST OF DALTON MN RATING: EF-4 ESTIMATED PEAK WIND: 170 MPH PATH LENGTH /STATUTE/: 9 MILES PATH WIDTH /MAXIMUM/: 650 YARDS FATALITIES: 1 INJURIES: 2 START DATE: JUL 8 2020 START TIME: 508 PM CDT START LOCATION: 6.5 W ASHBY / GRANT COUNTY / MN START LAT/LON: 46.09525 / -95.94205 END DATE: JUL 8 2020 END TIME: 539 PM CDT END LOCATION: 5 E DALTON / OTTER TAIL COUNTY / MN END LAT/LON: 46.17784 / -95.81200 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 NOTE: THE INFORMATION IN THIS STATEMENT IS PRELIMINARY AND SUBJECT TO CHANGE PENDING FINAL REVIEW OF THE EVENTS AND PUBLICATION IN NWS STORM DATA.
Modified July 10, 2020