SILVER SPRING, MD – A new category of Severe Thunderstorm Warnings will soon trigger alerts on smartphones nationwide.
For some time, the National Weather Service has been working on better conveying the severity and potential impacts of thunderstorms to the general public as a part of the ongoing Hazard Simplification (HazSimp) project. Starting on Wednesday, the agency will add a “damage threat” tag to all of its Severe Thunderstorm Warnings.
These tags, which have already been in use with Tornado and Flash Flood Warnings for awhile now, highlight the exact impacts expected from a particular storm, which helps to distinguish the difference between high-impact and low-impact events.
There will now be three damage threat categories for all future Severe Thunderstorm Warnings; “Base”, “Considerable”, and “Destructive”.
Base is the minimum criteria needed to warrant the issuance of a Severe Thunderstorm Warning. A thunderstorm must produce wind gusts in excess of 58 MPH and or quarter sized hail (1.00 inch) in diameter. This criteria remains unchanged and will not carry a “damage threat” tag, so no WEA alert will be triggered.
Thunderstorms that are producing at least 70 MPH wind gusts and or golf ball sized hail (1.75 inches in diameter) will now carry a “Considerable damage” tag within the text of the warning. This category will also not push a WEA alert.
Destructive is the highest damage threat category defined. For a Severe Thunderstorm Warning to carry this tag, a storm must be producing very large hail up to baseball size (2.75 inches in diameter) and or wind gusts of at least 80 MPH. These kinds of storms are very dangerous and require urgent action to protect human life. Given this, a WEA alert will automatically be pushed to smartphones within the warned area.
According to the Weather Service, only around 10 percent of severe thunderstorms across the country on average reach the destructive category each year. Most of these storms are either extreme damaging wind events such as derechoes, or supercell storms which typically produce very large hail.
In 2020, 13 of the 22 costliest weather disasters in the United States were the result of severe thunderstorms, including the costliest thunderstorm disaster in U.S. history; the powerful Iowa Derecho of August 10–11, racking up a damage bill of $11 billion.