EF2 Tornado — Cass, North Dakota

2007-07-15 · near Tower City, Cass, North Dakota

Event narrative

The tornado plowed through wooden power poles and viciously ripped up mature trees over its damage path. The tornado also damaged a sturdy pole shed, where the sidewall was caved in and the roof and rafters were torn off. It tore the roof off and collapsed an older barn, then lifted and threw a well-built two car garage from its slab foundation. The tornado crumpled one steel, four footing, high voltage power tower. In combination with extreme downburst winds, the collapse of this first tower helped initiate the collapse of dozens more of these power towers. Peak winds were estimated at 130 mph.

Wider weather episode

At 3 pm CST on the 15th, a stationary front was located from near Minot (ND) to Jamestown (ND) to near Sisseton (SD). South of the front, mid afternoon temperatures ranged in the mid 80s to lower 90s. To the north of the front, a meso-high had formed, with much cooler and drier air around it. The temperature across the boundary ranged from 89F at Minot, to 73F at Devils Lake, to 64F at Crookston. The upper air pattern had a western ridge and an eastern trough, putting the northern plains in northwest flow aloft. A strengthening upper jet also moved toward eastern North Dakota, giving this system good surface and upper level support.

A supercell thunderstorm developed over southern Steele County around 530 pm CST and tracked across western Cass County and into eastern Ransom County before weakening after 7 pm CST. Then, another supercell thunderstorm formed over northern Steele County around 725 pm CST. This storm tracked just west of the path of the first storm, again mainly hitting central Steele County, western Cass County, and eastern Ransom County, before weakening around 915 pm CST. Both thunderstorms tracked south-southeast at speeds between 40 and 50 mph and spawned multiple tornadoes which were embedded within the overall downburst wind and hail pattern.

The significant downburst wind and wind driven hail was seen in two partially overlapping paths, with each path from 5 to 7 miles wide and between 60 and 80 miles long (this damage path showed up clearly on satellite images). The strength of these winds is believed to have exceeded 80 mph with speeds over 100 mph in some localized areas. Hail sizes ranged from penny to hen egg sized.

Most areas received considerable hail damage at the same time as the strong winds. Law enforcement officials and witnesses stated that the hail often persisted for longer than 5 minutes and completely covered the ground. The hail damaged roofs, windows, and siding in many homes along the damage path. Stripped and decimated corn, bean, and wheat fields were typical along the entire storm path too. The ND Farm Service Administration estimated losses occurred on over 700,000 acres in five counties. Total crop losses may exceed $250 million, with other property losses from $15 to $20 million. Cass and Steele Counties received a Presidential Disaster Declaration.

View location on OpenStreetMap → (46.9300, -97.6065)

Source: NOAA Storm Events Database, event_id 48314. Narrative written by the NWS forecast office that issued the report.