Severe thunderstorms can be endangering to human lives but every severe storm is different. They can range from large hail storms, tornadoes, and cloud-to-ground lightning, to Derechos (widespread straight-line winds) and flash flooding. From August 2, the severity and potential impacts from thunderstorm winds and hail will be conveyed in an improved manner by the National Weather Service. Similar to the Tornado and Flash Flood Warnings it issues, the NWS will be adding a “damage threat” tag to Severe Thunderstorm Warnings.
The National Weather Service has classified Severe Thunderstorm Warnings into three categories — destructive, considerable, and base — in order of highest to the lowest threat of damage. These tags and additional messaging have been created so that immediate action can be taken for the specific threat.
Destructive Damage Threat
For a threat to be classified under this category, the hail should be the size of a baseball i.e. at least 2.75 inches in diameter, and/or come with thunderstorm winds of 80 mph. Warnings linked to this tag will set off a Wireless Emergency Alert (WEA) on smartphones within the concerned area automatically.
Considerable Damage Threat
For a threat to be categorized as “considerable” the hail should measure at least 1.75 inches in diameter i.e. the size of a golf ball and/or come with 70 mph thunderstorm winds. The WEA won’t be activated in this case.
Baseline severe thunderstorm warning
The criteria for this hasn’t been changed, so a 1 inch or quarter-sized hail and/or 58 mph thunderstorm winds will warrant this warning. The WEA won’t be enabled in this scenario either. So, when a damage threat tag is absent, the damage is believed to be at the base level.
Only 10 percent of all severe thunderstorms fall under the destructive category on average annually across the country. The new destructive thunderstorm category is meant to inform the public that they need to take urgent action.