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.

As of July 28, the National Weather Service (NWS) has begun better conveying the severity and potential impacts from thunderstorm winds and hail by adding a “damage threat” tag to severe thunderstorm warnings, similar to tornado and flash flood warnings already issued by the weather service.

The NWS has developed three categories of damage threat for severe thunderstorm warnings. The categories, in order of highest to lowest damage threat, are destructive, considerable, and base.

The additional messaging was designed to promote immediate action based on the threat.

The criteria for a destructive damage threat is hail with a diameter of at least 2.75 inches (baseball-sized) and/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 hail with a diameter of at least 1.75 inches (golf ball-sized) and/or 70 mph thunderstorm winds. This will not activate a WEA.

The criteria for a baseline or base severe thunderstorm warning remains unchanged: 1-inch (quarter-sized) hail and/or 58 mph thunderstorm winds. This also will not activate a WEA. When no damage threat tag is present, damage is expected to be at the base level.

According to the NWS, on average, only 10% of all severe thunderstorms reach the destructive category each year nationwide. Most of these storms are damaging wind events such as derechoes. Some of the larger, more intense thunderstorms, called supercell storms, can typically produce very large hail in their path.

The new destructive thunderstorm category conveys to the public that urgent action is needed: A life-threatening event is occurring and may cause substantial damage to property.

All National Weather Service severe thunderstorm warnings will continue to be issued and broadcast via weather.gov, NOAA weather radio, the emergency alert system, and through dissemination systems to 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 WEA for many of these high-impact events, including the costliest thunderstorm in US history, the $11 billion derecho that struck Iowa in August 2020.

Learn how to stay safe in a severe thunderstorm at weather.gov/safety/thunderstorm. Knowing what to do before, during, and after severe weather can increase the chances of survival.

The National Oceanic and Atmospheric Administration Storm Prediction Center provides forecasts of severe weather up to seven days in advance, and severe thunderstorm and tornado watches several hours before storms form. The National Weather Service operates under the umbrella of NOAA.