Tornado in North Dakota was the first at EF5 strength in a dozen years

(AP) — A deadly tornado that tore across North Dakota this summer has been upgraded to an EF5 with winds over 200 mph, the strongest classification of tornado and the first on American soil in 12 years, meteorologists said Monday.

The tornado on June 20 in Enderlin caused significant damage across the region and killed three people. The tornado touched down on the ground for just over 12 miles (19 kilometers), and at its largest, was 1.05 miles wide (1.69 kilometers).

Meteorologists from the National Weather Service in Grand Forks estimated that the tornado had winds in excess of 210 mph (338 kph), according to a Weather Service analysis released on Monday.

The 1999 Bridge-Creek Moore tornado in Oklahoma holds the record of the strongest winds ever recorded at 321 mph (517 kph).

Since the National Weather Service began using Enhanced Fujita scale in 2007, there have been 10 tornadoes categorized as EF5.

“In the last kind of 12 years, there’s been several strong tornadoes that have come close, but there haven’t been known damage indicators at that time to support the EF5 rating,” said Melinda Beerends, meteorologist in charge at the National Weather Service in Grand Forks. “It’s hard sometimes to get tornadoes to hit something.”

This summer’s tornado destroyed farmsteads, tipped over fully-loaded rail cars, toppled transmission towers and uprooted trees. One tanker car had been flung far from the rest.

Meteorologists from the Grand Forks office headed into the field the following morning to examine the damage. It usually takes from days to weeks to determine the strength of a tornado by its wind speed, which meteorologists do by examining the damage to buildings and trees. This tornado took much longer to analyze because the damage it inflicted on the rail cars was unusual.

The initial estimate for the tornado in the days afterward was an EF3.

The tornado was caused by warm, moist air in place which is ripe for a thunderstorm, Beerends said. But there was also a high amount of wind shear, which is a variation of wind speed and direction that created the conditions for the tornado.

Two men and a woman were killed at two locations near Enderlin, about 40 miles (65 kilometers) southwest of Fargo. Thousands of homes lost power during the storm.

One farmstead had its foundation swept clean, with just the basement remaining and debris scattered downwind.