Thursday, August 5, 2021 - Severe thunderstorms can be life-threatening, but not all severe storms are the same. Hazardous conditions range from tornadoes, large hail storms and widespread straight-line winds called derechoes, to cloud-to-ground lightning and flash flooding.
As of Monday, Aug. 2, the National Weather Service will better convey the severity and potential impacts from thunderstorm winds and hail by adding a “damage threat” tag to severe thunderstorm warnings, similar to the NWS's tornado and flash flood warnings.
The NWS has developed three categories of severe thunderstorm warning damage threats, The categories, in order of highest to lowest damage threat, are destructive, considerable and base. These tags and additional messaging are designed to promote immediate action, based on the threats.
The criteria for a “destructive” damage threat is at least 2.75-inch diameter (baseball-sized) hail and/or 80 mph winds. Warnings with this tag will automatically activate a wireless emergency alert (WEA) on smartphones within the warned area.
The criteria for a “considerable” damage threat is at least 1.75-inch diameter (golf ball-sized) hail and/or 70 mph winds This will not activate a WEA.
The criteria for a baseline or “base” severe thunderstorm warning remains unchanged, 1-inch (quarter-sized) hail and/or 58 mph thunderstorm winds. This will not activate a WEA. When no damage threat tag is present, damage is expected to be at the base level.
On average, only 10 percent of all severe thunderstorms reach the destructive category each year nationwide. Most of these storms are damaging wind events such as derechoes and some of the larger, more intense thunderstorms, called “supercell” storms that can typically produce very large hail in their path. 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. Storms categorized as destructive will trigger WEAs to cell phones.
Laura Brown, KXMX Staff Writer
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