National Weather Service to send mobile alerts for ‘destructive’ thunderstorms

Officials with the National Weather Service announced Thursday that beginning next month, new alerts will be going to cellphones when forecasters issue warnings for severe thunderstorms with the potential to be destructive.

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Forecasters also announced that severe thunderstorm warnings issued by the agency will get new damage threat tags based on the strength of a storm’s winds or the size of its hail. Under the new system, destructive threats are categorized as storms with winds of at least 80 mph or “baseball-sized” hail that is at least 2.75 inches in diameter.

Starting Aug. 2, alerts for severe thunderstorms deemed to be potentially destructive will be sent through the Federal Emergency Management Agency’s Wireless Emergency Alerts system. The system is already used to send AMBER alerts and other extreme weather warnings to cellphones.

“The new destructive thunderstorm category conveys to the public urgent action is needed, a life-threatening event is occurring and may cause substantial damage to property,” NWS officials said.

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Forecasters will also note when a storm poses a “considerable” damage threat, defined as having winds of 70 mph and “golf ball-sized” hail that is at least 1.75 inches in diameter, though such storms wouldn’t trigger FEMA’s Wireless Emergency Alerts system. Officials said severe thunderstorm warnings sent without any damage threat tag will be categorized as “base”-level threats, with quarter-sized hail of about one inch or winds of 58 mph.

In addition to the cellphone alerts, officials said severe thunderstorm warnings will continue to be shared on weather.gov, and through NOAA Weather Radio and the Emergency Alert System.

Officials with NWS said that only about 10% of severe thunderstorms reported nationwide each year reach the destructive category. A majority of these storms are damaging wind events, such as derechoes, and “supercell” storms which can produce very large hail, according to forecasters.