Severe Thunderstorm
Watch vs. Warning
The NWS issues severe thunderstorm watches and warnings every storm season. They sound similar but mean very different things. Here's how to tell them apart and what action to take.
What Makes a Thunderstorm "Severe"?
Not every thunderstorm is severe. The National Weather Service classifies a thunderstorm as severe when it produces any of the following:
Winds 58+ mph
Strong enough to snap tree limbs, down power lines, and damage roofs. At 70+ mph, straight-line winds can cause damage comparable to a weak tornado.
Hail 1 inch or larger
Quarter-sized or bigger. One-inch hail dents cars and cracks windows. Baseball-sized hail (2.75 inches) can punch through roofs and is lethal if it hits you.
Tornado
If a tornado is detected, the NWS issues a tornado warning instead. But severe thunderstorm warnings often precede tornado warnings — the same storm can produce both.
Watch vs. Warning
Severe Thunderstorm Watch
Issued by the Storm Prediction Center. Conditions are favorable for severe thunderstorms in your area over the next several hours. Covers a large region — often multiple counties or states. Be prepared to act.
Severe Thunderstorm Warning
Issued by your local NWS forecast office. A severe thunderstorm has been detected on radar or observed by a spotter in your area. This is an immediate threat. The warning specifies which counties are affected and the storm's direction of travel. Take action now.
What to Do During a Severe Thunderstorm Warning
Get Inside
Move indoors to a sturdy building. Stay away from windows. If you're in a mobile home, consider moving to a sturdier structure — mobile homes are especially vulnerable to straight-line winds.
If Driving
Pull over if you can do so safely. Don't park under trees or overpasses. Stay in your vehicle with your seatbelt on — a car provides better protection from hail and debris than being outside.
Lightning Safety
All thunderstorms produce lightning, not just severe ones. If you can hear thunder, you're within striking distance. Move indoors. Avoid plumbing and wired electronics during the storm.
Watch for Upgrades
Severe thunderstorm warnings can be upgraded to tornado warnings if rotation is detected. Keep monitoring alerts — if a tornado warning is issued, move to an interior room on the lowest floor immediately.
Damage Tags: Considerable and Destructive
Since 2021, the NWS adds damage threat tags to severe thunderstorm warnings when conditions are especially dangerous:
Base (no tag)
Standard severe thunderstorm warning. 58–70 mph winds or 1–1.75 inch hail. Dangerous but not catastrophic.
Considerable
70–80 mph winds or 1.75–2.75 inch hail. Significant damage expected. Mobile homes at serious risk. Treat this with the same urgency as a tornado warning.
Destructive
80+ mph winds or 2.75+ inch hail. This triggers Wireless Emergency Alerts (WEA) on cell phones — the same system used for tornado warnings. Seek shelter immediately. Damage will be severe.
Get Severe Thunderstorm Alerts on Your Phone
StormCast delivers every NWS severe thunderstorm watch and warning for your location within seconds of being issued. The app also shows active alert polygons on live radar so you can see the storm's position and direction of travel.
Download StormCast Free on Google Play