The Fargo F5 Tornado of 20 June 1957: Historical Re-Analysis and Overview of the Environmental Conditions

Chauncy J. Schultz
National Weather Service
North Platte, Nebraska

David J. Kellenbenz
National Weather Service
Grand Forks, North Dakota

Jonathan Finch
National Weather Service
Dodge City, Kansas

ABSTRACT

     On the evening of 20 June 1957, an F5 tornado struck the city of Fargo, North Dakota killing 13 people and injuring over 100. This tornado was researched extensively by Dr. Tetsuya Fujita, and became a basis for his creation of the F scale (later developed in 1971) and coining of the phrases wall cloud, collar cloud and tail cloud (Fujita 1960).The Fargo tornado was one in a family of at least five tornadoes produced by a single, long-lived, cyclic supercell. Observational data from 1957 were used to examine the synoptic and mesoscale environment from the perspective of present-day tornado research, with a focus on the possibility of an outflow boundary enhancing the tornado potential near Fargo. Strong instability, strong vertical wind shear, high storm-relative helicity (SRH), favorable storm-relative flow (SRF) and lowered lifted condensation levels (LCLs) seemed to play a pivotal role in the strength and longevity of the tornado. In addition, boundary-layer moisture appeared to be enhanced via evapotranspiration (ET) and moisture convergence. Approximately 200 photographs of the supercell and tornado also provided better insight to the storm-scale environment, which was not well understood in 1957.



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