EF4 tornado in Grand Forks County, North Dakota

This tornado began in Traill County about 3 miles north-northeast of Mayville at 349 PM CDT. The tornado crossed into Grand Forks County and tracked for an additional 8 miles to about 10 miles west of Thompson. The total track length was roughly 17 miles. One well constructed house near Holmes was completely swept from its foundation and destroyed along with several other farm buildings. Peak winds were estimated at 185 mph.

Conditions were ripe by the afternoon of the 17th for a major severe weather outbreak. A surface low had moved into east central North Dakota with an occluded front extending to the southeast. Warm and humid air was in place ahead of the front, with a much drier airmass pushing in behind it. The 500mb low was located over northwest North Dakota with a nice southwest to northeast upper jet pushing into eastern North Dakota. Two lines of convection formed by late afternoon, one from Roseau County down toward Eastern Otter Tail County and the other over east central North Dakota. Nearly all the cells that formed took on a classic hook shape with rotation very evident on radar imagery. Multiple tornado warnings were issued before the event wound down by mid evening. The strongest tornadoes were determined to be EF4 tornadoes, two in west central Minnesota and one in northeast North Dakota.