New descriptive threat categories being added to thunderstorm warnings
JACKSON COUNTY, Ky. (WTVQ/Press Release) – The National Weather Service has recognized that not all severe storms are the same, leading to an update in Severe Thunderstorm Warnings.
Beginning Aug. 2, a “damage threat” tag will be added to Severe Thunderstorm Warnings to better illustrate the severity and potential impacts from thunderstorm winds and hail.
Three categories of damage threat have been developed. In order of highest to lowest damage threat, the categories are destructive, considerable and base. The goal of these tags and additional messaging are 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 thunderstorm 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 thunderstorm winds. This will not activate a WEA.
The criteria for a baseline or “base” severe thunderstorm warning remains unchanged, 1.00 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.
Typically, only 10% of all severe thunderstorms get to the destructive category each year across the nation. 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 a WEA to your cell phone.
All National Weather Service Severe Thunderstorm Warnings will continue to be issued and distributed via weather.gov, NOAA Weather Radio, Emergency Alert System and through dissemination systems to our emergency managers and partners. The addition of damage threat tags are part of the broader Hazard Simplification Project to improve communication of watches and warnings to the public.
Thirteen of the 22 costliest weather disasters in 2020 were severe thunderstorms. The new “destructive” tag would have activated a Wireless Emergency Alert for many of these impactful events, including the costliest thunderstorm in U.S. history, the $11 billion derecho that affected Iowa in August 2020.
For more information, visit the National Weather Service’s Severe Weather 101 webpage.