LITTLE ROCK, Ark.- Starting Monday, August 2nd, 2021, the National Weather Service will be implementing a new severe thunderstorm warning structure based on the threat of damaging wind or hail. These kinds of warnings will now include impact-based warning tags.
Keep in mind the threshold to issue a severe thunderstorm warning will not change. The minimum threshold for a severe warning to be issued is for wind speeds 58 mph or greater and or hail 1″ in diameter or larger.
The change being put in place is to help highlight different levels of severity that a severe thunderstorm is capable of producing. Up until now, a severe thunderstorm warning would be issued and could cover a range of severity when it comes to thunderstorms. While the warning text would display why the warning was issued (wind speed and hail size), it could be overlooked. These impact tags would make it easier to locate and read that crucial information.
If you look at the new format above, there will be two new tags that can be flagged with a severe thunderstorm warning. Again, for a “base” severe thunderstorm warning, nothing will change.
If meteorologists at the National Weather Service detect a thunderstorm is capable of producing straight-line winds of 70-80 mph and or 1.75″ (golf ball) to 2.5″ (tennis ball) diameter hail, the warning will be tagged with “considerable” damage threat.
If a thunderstorm is capable of producing straight-line wind speeds of 80 mph or greater and or hail 2.75″ (baseball) diameter hail or larger, the warning will be tagged with a “destructive” damage threat.
When a severe thunderstorm warning is tagged with a “destructive” damage threat, that will allow the warning to be sent out to cell phones via the wireless emergency alert (WEA) system. This will be a brand new capability with severe thunderstorm warnings. Up to this point, only Tornado Warnings and Flash Flood Warnings with “considerable” or “catastrophic” tags were sent out via the WEA system.
According to the National Weather Service, 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 derechoes and some of the larger, more intense thunderstorms, called “Supercell” storms that can typically produce very large hail in their path. 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.
All National Weather Service severe thunderstorm warnings will continue to be issued and distributed via weather.gov, NOAA Weather Radio, Emergency Alert System, and through dissemination systems to our emergency managers and partners (i.e. television). The addition of damage threat tags is part of the broader Hazard Simplification Project to improve communication of watches and warnings to the public.