New Damage Threat Categories for Severe Thunderstorm Warnings

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.

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.

Three categories of damage threats for Severe Thunderstorm Warnings were developed. The categories, in order of lowest to highest damage threat, are base, considerable and destructive. These tags and additional messaging are designed to promote immediate action, based on the threats

Here are the three categories:

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.

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 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.

If the considerable or destructive damage threat categories are used, it will be listed at the bottom of the severe thunderstorm warning (see below for an example):

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 a WEA to your cell phone.

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.