ADVERTISEMENT

ADVERTISEMENT

ADVERTISEMENT

ADVERTISEMENT

How are tornadoes rated? WDAY's John Wheeler breaks it down

The National Weather Service has classified the tornado that swept across Otter Tail County, generating winds of 170 mph with very little warning, as an EF4 on the Enhanced Fujita scale.

WDAY's Matt Henson spoke with meteorologist John Wheeler to explain how the NWS made its determination, and how rare a tornado like this is.

Matt: So John, how do they determine did they determine the wind speed of this tornado?

John: You don't have a measuring anemometer inside a tornado so what the national weather service does is they look at structures, different types of structures, how well built they were, tree and the type of damage that occurred. What you see here is well machine shed that had been swept clean, that was the first indicator that this tornado was producing EF4 damage of winds at least 170 mph. A few minutes later the tornado hit a house and again you can see the house has been utterly destroyed. In fact, the people who were injured were down in the basement taking shelter, but it was debris that fell in on top of them. This is the second indicator of 170 mph wind and EF4 damage.

Matt: The people there were in the basement when the tornado hit and that is where people are supposed to go during a severe weather event.

ADVERTISEMENT

John: Most of the time if you are in the basement, you are going to be fine in a tornado. EF4's and EF5's represent fewer than 2% of all tornadoes and the vast majority of tornado fatalities. There is not much you can do when a tornado this powerful hits your house.

Matt: John, how do they determine the strength of the tornado when it's in the wide-open prairie?

John: Sometimes if the tornado is moving across a cornfield, there is not damage except for flattened corn. It doesn't take tremendous wind to flatten corn. So often times it's possible that a tornado is doing incredible damage with incredible wind speed that we can't actually measure.

Matt: John, when was the last time we saw an EF4 tornado in our region?

John: It been 10 years since we saw an EF4 tornado within the greater area. The last one actually touched down near Doran, south of Breckenridge in Wiklin County on August 7 of 2010. There were four EF4 tornadoes that summer. They touched down on June 17. One touched down in the Burbank/Hillview area of Otter Tail County. There was also another one near Bluffton in Otter Tail County, and that moved into Wadena where it did considerable damage. The third one touched down in the Portland, Hunter and Thompson area of Traill and Grand Forks counties.

Matt Henson is an Emmy award-winning reporter/photographer/editor for WDAY. Prior to joining WDAY in 2019, Matt was the main anchor at WDAZ in Grand Forks for four years.

ADVERTISEMENT

What To Read Next
Get Local

ADVERTISEMENT