Severe thunderstorms can be life threatening, but not all severe storms are created equal. Dangerous conditions range from tornadoes, large hail storms, and widespread straight-line winds called rights to cloud-to-ground lightning and flash flooding. Beginning August 2, the National Weather Service will better convey the severity and potential impacts of storm winds and hail by adding a “threat of damage” label to Severe Storm Warnings, similar to our Tornado Warnings. and flash floods.
THREAT CATEGORIES OF “DESTRUCTIVE” AND “SIGNIFICANT” DAMAGE
The National Weather Service developed three categories of damage threats for severe storm warnings. The categories, in order from greatest to least threat of harm, are destructive, substantial, and vile. These additional labels and messages are designed to promote immediate, threat-based action.
A wireless emergency alert (cell phones) will be issued for a severe thunderstorm that meets the criteria for a threat of destructive damage.
Criteria for a threat of destructive damage is hail of at least 2.75 inches in diameter (the size of a baseball) and / or storm winds of 80 mph. Warnings with this label will automatically trigger a wireless emergency alert (WEA) on smartphones within the warned area.
Criterion for a threat of significant damage is hail of at least 1.75 inches in diameter (the size of a golf ball) and / or storm winds of 70 mph. This will NOT activate a WEA.
Criteria for a baseline or base severe storm warning remain unchanged, 1.00-inch (quarter-size) hail and / or 58-mph storm winds. This will not activate a WEA.
When there is no threat of harm tag, the harm is expected to be at the base level.
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 rights and some of the larger and more intense thunderstorms, called “supercell” storms that can typically produce very large hail in their path. The new category of destructive storms conveys to the public that urgent action is needed, a life-threatening event is occurring and may cause substantial property damage. Storms categorized as destructive will trigger a WEA on your cell phone.
All severe thunderstorm advisories from the National Weather Service will continue to be issued and distributed through weather.gov, NOAA’s weather radio, the emergency alert system, and through outreach systems to our emergency managers and partners. The addition of damage threat labels is part of the broader Risk Simplification Project to improve the communication of alerts and warnings to the public.
Thirteen of the 22 costliest weather disasters in 2020 were severe thunderstorms. The new destructive label would have triggered a wireless emergency alert for many of these shocking events, including the costliest electrical storm in US history, the $ 11 billion claim that hit 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.
NOAA’s Storm Prediction Center provides severe weather forecasts up to seven days in advance, and alerts for severe thunderstorms and tornadoes several hours before storms form.