Why A Severe Thunderstorm Warning Could Save Your Life

Derecho Flips Trucks In Illinois

Severe thunderstorms pose a threat to both life and property, and that's why warnings from the National Weather Service should be taken seriously.

If you're like most people, tornado warnings grab your attention more than severe thunderstorm warnings.

We all know about the destructive power of tornadoes, particularly those violent tornadoes of EF4 and EF5 intensity on the Enhanced Fujita scale, capable of demolishing homes, leaving only a pile of rubble or a foundation swept clean.

However, severe thunderstorms are also dangerous and occasionally deadly.

What Is A Severe Thunderstorm?

The NWS defines a severe thunderstorm as one which is capable of at least one of the following:

Here are reasons why you should never disregard a severe thunderstorm warning issued by the National Weather Service.

• Hail at least 1 inch in diameter
• Wind gusts of at least 58 mph
• Tornadoes

Much More Common Than Tornadoes

You're much more likely to have a severe thunderstorm warning issued for your area than a tornado warning. Over 21,000 severe thunderstorm warnings were issued by the NWS in 2024, over five times the number of tornado warnings (3,635).

But just because they can happen more often doesn't mean they're not dangerous. Here are the reasons why.

Damaging Winds

As senior meteorologist Chris Dolce detailed in a previous article, there are over 17,000 reports of severe thunderstorm high winds or damage from those winds across the country each year, on average. That amounts to about 70% of all severe weather reports, according to NOAA's Storm Prediction Center.

It doesn't take a tornado to produce damage from severe thunderstorms.

Severe thunderstorm winds may be strong enough to at least down tree limbs or knock out power. In some cases, they may down entire trees, crashing through homes and vehicles or whatever else is in their way. Imagine one crashing through your bedroom while you're sleeping.

Sometimes in late spring or summer, thunderstorms may form a long-lived, fast-moving complex of high winds known as a derecho. These are capable of widespread tree damage and power outages, as well as some structural damage from wind gusts that can top 100 mph in the extreme, the equivalent of an EF1 tornado.

According to the NWS, 36 deaths were attributed to thunderstorm winds in the U.S. in 2023, more than those killed by lightning.

What you should do:

• Before thunderstorms threaten, keep healthy trees trimmed and remove any trees or limbs, particularly dead ones, leaning toward your house.
• If you have large trees around your home, seek shelter on the lowest floor, preferably in the basement, away from windows if a severe thunderstorm warning is issued that mentions the potential for damaging straight-line winds.
• If you hear the word derecho mentioned in any forecast for your area, or see "wind gusts over 70 to 75 mph" noted in a severe thunderstorm warning, take shelter immediately as you would for a tornado warning.

Destructive Hail

There were over 5,300 reports of severe hail – at least 1 inch diameter – in the U.S. in 2024, according to NOAA's Storm Prediction Center, making up 22% of all severe weather reports that year.

Over 800 of those reports were of hail 2 inches in diameter or larger, roughly the size of a hen's egg.

It only takes 1-inch diameter hail - roughly the diameter of a quarter - to damage roof shingles. Golf-ball-sized hail, roughly 1.75 inches in diameter, can put dents in your vehicle. Damage quickly becomes more serious with more rare baseball-sized (smashes vehicle windshields) and softball-sized (punches holes in roofs) hail. 

Furthermore, thunderstorm winds can whip these hailstones much like a baseball pitcher. Your home's exterior could be a total loss, with its siding destroyed, numerous holes in your roof, even windows smashed. The St. Louis metro area had a pair of billion-dollar hailstorms in April 2012 and April 2001.

While exceedingly rare, deaths from large hail have occurred. Most recently, a pizza deliveryman in Fort Worth, Texas, was killed by baseball- to softball-sized hail on March 28, 2000. Ninety-three people were injured by large hail in the U.S. in 2024, according to NOAA.

What you should do:

• If a severe thunderstorm warning for your area mentions the threat of large hail, move indoors immediately and, if there's time, move your vehicle(s) into a garage, parking deck or some covered area.
• Do not park under a highway overpass. If many try to do the same, the highway may become blocked. Highway overpasses are a terrible option for taking shelter in a tornado if caught outdoors. This can result in a potentially deadly situation for other people.

(MORE: Don’t Do This When Severe Weather Strikes and You Are Driving)

Tornadoes Still Can Form

Occasionally, you'll see the following wording in National Weather Service severe thunderstorm warnings: "Severe thunderstorms can and sometimes do produce tornadoes with little or no advance warning."

Sounds scary, doesn't it?

This wording may be in severe thunderstorm warnings when a tornado watch is already in effect, yet the severe thunderstorm does not yet show sufficiently strong rotation on Doppler radar or via storm spotter reports.

Therefore, the NWS may first issue a severe thunderstorm warning for a strengthening storm based on the threat of large hail and perhaps damaging straight-line winds.

However, in the span of minutes, the intensifying thunderstorm may quickly develop low-level rotation that, under the right conditions, could lead to a tornado.

Sometimes, brief tornadoes form quickly on the leading edge of a long line of severe thunderstorms with otherwise damaging straight-line winds. 

These typically brief tornadoes may occur during the night, or may be wrapped in rain and hard to see.

What you should do:

• If an NWS severe thunderstorm warning mentions a "tornado is possible," seek shelter as if it was a tornado warning, based on this potential for a tornado to quickly develop.

Frequent Lightning

Don't forget the threat from lightning in a severe thunderstorm.

While any ordinary midsummer thunderstorm can produce lightning, severe thunderstorms can produce more frequent cloud-to-ground lightning.

This is particularly the case with long squall lines of severe thunderstorms capable of damaging straight-line winds, as well as classic late-spring, summer and fall clusters of severe thunderstorms in the South, Midwest and East.

In these cases, thousands of cloud-to-ground lightning strikes can occur in the thunderstorm cluster over one hour or less. Lightning strikes can persist for a half-hour or slightly longer after the main line of thunderstorms with the highest wind gusts passes.

What you should do:

• If you hear thunder or see lightning while outside, you're in danger. Move indoors as soon as possible.
• Avoid contact with electrical devices, corded phones, metal pipes, etc. while taking shelter indoors.
• Stay inside for at least 30 minutes after hearing the last clap of thunder.

Jonathan Erdman is a senior meteorologist at weather.com and has been covering national and international weather since 1996. Extreme and bizarre weather are his favorite topics. Reach out to him on Bluesky, X (formerly Twitter) and Facebook.