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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 Derechos to cloud-to-ground lightning and flash flooding. Starting August 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 our Tornado and Flash Flood Warnings.
“Destructive” and “Considerable” Damage Threat Categories
We developed three categories of damage threat for Severe Thunderstorm Warnings. In order of highest to lowest damage threat, the categories are destructive, considerable, and base. The NWS designed these tags and additional messaging 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 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 or 70 mph thunderstorm winds. It will not activate a WEA.
- The criteria for a baseline or “base” severe thunderstorm warning remains unchanged, 1.00 inch (quarter-sized) hail or 58 mph thunderstorm winds. It will not activate a WEA. When no damage threat tag is present, the damage should be at the base level.
On average, only ten percent of all severe thunderstorms reach the destructive category each year nationwide. Most of these storms have damage wind events such as Derechos and some of the more significant, more intense thunderstorms, called “Supercell” storms that can typically produce giant hail in their path. The new destructive thunderstorm category conveys that urgent public action is needed, a life-threatening event is occurring and may cause substantial property damage. 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 dissemination systems to our emergency managers and partners. The addition of damage threat tags is 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 Derechos that affected Iowa in August 2020.
Learn how to stay safe in a severe thunderstorm. Knowing what to do before, during, and after severe weather can increase your chances of survival.
The NOAA Storm Prediction Center provides severe weather forecasts up to seven days in advance, and severe thunderstorms and tornado watch several hours before storms form.
Explore our Severe Weather 101 webpage.