Severe Weather Awareness Week 2021 — 1st Topic: Severe Thunderstorms

Thunderstorms are a familiar occurrence in Alabama. In Birmingham, we average 57 thunderstorm days a year. Mobile averages 79 thunderstorm days. Many find storms to be interesting and even thrilling, but they are dangerous creatures that deserve our respect.

By definition, thunderstorms contain lightning, the underrated killer. Thunderstorms also produce damaging winds, hail, flooding, and tornadoes. For a storm to be considered “severe”, it must contain at least one of the following criteria:

• Wind gusts of 58 MPH or greater
• Hail of 1 inch in diameter or greater
• A tornado (upgrades to a tornado warning)

Although lightning can be deadly, the National Weather Service doesn’t use it to define a severe thunderstorm. If it did, every thunderstorm would be severe, by definition. Also, excessive rainfall may lead to deadly flash flooding, heavy rain is not considered severe. Flood threats are handled through a separate set of watches and warnings from the NWS Birmingham.

Image from The National Severe Storms Laboratory (

One event that can cause damage and injuries during severe thunderstorms are straight-line winds. Damaging winds occur much more frequently than tornadoes and can be just as damaging. They can exceed 100 mph. Trees and power lines can be knocked down, mobile homes can be overturned, and well-built homes and buildings damaged.

Image from The National Severe Storms Laboratory (

Another event that can cause damage and injuries during severe thunderstorms is hail. Hail is most common in the spring in Alabama when atmospheric conditions make it most likely that the ice can reach the ground. Hail can cause severe damage to automobiles and even to buildings, damaging roofs and windows. Hail injuries are rare but do happen. Hail can also cause deaths, as happened on March 28, 2000, when a man in Fort Worth, Texas was struck by a baseball-sized hailstone. There have been five recorded hail fatalities in U.S. history. So while it is not a frequent killer, it can still be deadly. To be safe, just don’t get caught outside in a thunderstorm.

Tornadoes are another event that can happen during severe thunderstorms. We’ll discuss tornadoes on Wednesday.

The primary safety rule for dealing with thunderstorms is to be in a well-built structure, away from windows. This will protect you from the hail and non-tornadic winds. If you are caught outside, find shelter immediately.

On Tuesday, we’ll take a look at flooding and flash flooding.

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