National Weather Service creates ‘destructive’ thunderstorm warning based on damage threats


ST. LOUIS – Not all severe thunderstorms are created equal. The National Weather Service is making some changes to its warnings in order to better convey the potential impacts of these storms.

Severe storms can be life-threatening, bringing hazardous conditions ranging from tornadoes, large hail, widespread straight-line winds or derechos, to dangerous lightning and flash flooding. Now there’s a clearer picture of what to expect when a warning is issued because they’ll be categorized into three tires of damage threats.

Tier 1 is the lowest damage threat, is a base severe thunderstorm warning for winds 60 to 70 miles per hour and hail quarter to ping pong ball sized.

Tier 2 is for considerable severe thunderstorm warnings for 70 to 80 mile per hour winds or hail from golf ball-sized to tennis ball-sized

And Tier 3 is destructive for 80-mile per hour plus winds and hail larger than baseball-sized.

“So the main impact on the general public for these destructive severe thunderstorm warnings. These destructive severe thunderstorm warnings now are going to cause all people’s cellphones to go off via these wireless emergency alerts or WEA for short,” said Kevin Deitsch, warning coordination meteorologist with the National Weather Service Office in St. Louis. “So if we issue a severe thunderstorm warning with this dangerous level, this 80 mile per hour wind or baseball-sized hail or larger, that’s going to cause your cell phones to go off to let everyone know that a destructive thunderstorm is on the way.”

On average, only 10 percent of all severe thunderstorms reach the destructive category each year, nationwide. But just last year on Aug. 10 and 11, we had the costliest storm in U.S. history when a derecho moved across Iowa.

“Eighty to 100 mile per hour winds even some pockets of 120 miles per hour, just straight-line winds. Not even a tornado. So it’s these kinds of thunderstorms that people really need to know about. Even though it’s not a tornado, it’s doing damage like or even worse than a tornado sometimes,” Deitsch said.

And with these devastating storms, another way to help warn the public could save lives.

“So we are working with local county emergency managers on their siren policies for these new severe destructive thunderstorm warnings,” said Deitsch. “As I mentioned, they will set off your cellphone alerts, so we’re working with county emergency managers on if it should sound the sirens as well. So those decisions will be made at the local level but we are in discussions with them of exactly how that will work.”

Moving forward, tornado sirens may sound when a severe thunderstorm warning with a destructive tag is issued. Straight-line winds can be just as dangerous and cause as much damage as a tornado so immediate action needs to be taken either way.

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