Not All Storms Are The Same

9/3/2021 (Permalink)

Powerful Thunderstorms

Severe thunderstorms and the hazardous conditions they produce – cloud-to-ground lightning; hail; tornadoes; flash flooding – are often part of the forecast in Northeast Tennessee during the warmer months. They can be forecasted ahead of time or occur unexpectedly, with little or no warning. Large hail can damage property such as roofs and windows, a lightning strike can cause a destructive fire, and whipping winds can uproot trees and break off branches onto properties. Any one of these threats in combination with excessive rain, can lead to considerable structural damage.

NWS classifies a thunderstorm as severe when it can produce 58 mph winds or greater and/or one-inch or larger hail. Beginning Aug. 2, 2021, Severe Thunderstorm Warnings have two new damage threat categories designed to promote immediate action, ‘destructive damage’ and ‘considerable damage.’

• The criteria for a ‘destructive’ thunderstorm damage threat is 80 mph winds or greater and/or 2.75-inch diameter hail (baseball-size). This warning will activate Wireless Emergency Alert (WEA) on smartphones, similar to tornado and flash flood warnings.
• The criteria for a ‘considerable’ thunderstorm damage threat is 70-79 mph winds and or 1.75-inch diameter hail (golf ball-sized). This will not activate WEA on smartphones.

Each year, nationwide, only 10% (10,000 of 100,000) of all severe thunderstorms reach the destructive category, on average. Most of these storms are damaging wind events, such as derechos (straight-line winds) and supercell thunderstorms. According NOAA’s National Centers for Environmental Information (NCEI), 13 of the 22 costliest weather disasters in 2020 were severe thunderstorms.