National Weather Service United States Department of Commerce

Flash Flood Watches in Southeast and Tennessee Valley; Critical Fire Weather in California; Severe Weather in Upper Midwest

Flash flood watches are in effect today in parts of the Southeast and Tennessee Valley from organized areas of heavy to excessive rainfall. Meanwhile, critical fire weather conditions are likely across northern California with offshore winds and dry conditions. Finally, a strong cold front will produce severe thunderstorms across the Upper to Mid Mississippi Valley. Read More >

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. 

As of August 3, 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 Wireless Emergency Alert (WEA) on smartphones. 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 (WEA) on smartphones within the warned area.

 

Click here for a pdf of this image.

 

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 the August 10, 2020 derecho and some of the more intense rotating thunderstorms, called “Supercell” storms that can typically produce very large hail in their path, such as the Illinois record hail size in Minooka on June 10, 2015. 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 beforeduring, and after severe weather can increase your chances of survival.

For more on these new Severe Thunderstorm Warning categories, see this national news release

Thank you to NWS Paducah for use of their web content for this news story.