KinwarnSevere thunderstorm watch vs. warning: what to know
A severe thunderstorm watch means storms with large hail or damaging winds are possible over a wide area in the next several hours. A severe thunderstorm warning means a severe storm is happening or about to hit your area, so go inside a sturdy building now.
A severe thunderstorm watch and a severe thunderstorm warning use almost the same words. The difference is timing. A watch means severe storms could form. A warning means one is happening or about to hit your area.
What makes a thunderstorm severe
The NWS calls a thunderstorm severe when it produces at least one of these:
- Hail 1 inch across or larger, about the size of a quarter
- Wind gusts of 58 mph or stronger
- A tornado
Lightning does not count toward the definition, even though every thunderstorm has it. Some severe storms go far past the minimum, with hail larger than softballs or winds over 100 mph. Heavy rain from these storms can also cause flash flooding.
Severe thunderstorm watch: be prepared
The Storm Prediction Center issues a severe thunderstorm watch when conditions favor organized storms with large hail or damaging winds. Watches cover a large area, often many counties or even several states, and usually last several hours.
During a watch, stay informed and be ready to act if a warning is issued. It is a good time to make sure your phone alerts and weather radio are on, and to think about where you would go if a storm hits.
Severe thunderstorm warning: take action
Your local NWS office issues a severe thunderstorm warning when radar shows a severe storm, or when a trained spotter or law enforcement officer reports one. The warning covers an area about the size of a city or small county and usually lasts about an hour. It can be issued without a watch in effect.
Three levels of severe thunderstorm warning
Since August 2021, the NWS has added damage threat tags to its most dangerous severe thunderstorm warnings.
| Level | Hail | Wind | Phone alert (WEA)? |
|---|---|---|---|
| Base (no tag) | 1 inch (quarter) | 58 mph | No |
| Considerable | 1.75 inches (golf ball) | 70 mph | No |
| Destructive | 2.75 inches (baseball) | 80 mph | Yes |
A storm can reach a level by hail, by wind, or both. Only destructive warnings trigger Wireless Emergency Alerts on phones in the warned area. The NWS says that on average, about 10 percent of severe thunderstorms reach the destructive level each year.
That means most severe thunderstorm warnings will not set off an emergency alert on your phone. You need another way to hear about them, such as a NOAA Weather Radio, local TV or radio, or a weather app. See how to get tornado warnings for options.
Tornadoes can happen too
Severe thunderstorm warnings are mainly about hail and wind. But the NWS notes that severe thunderstorms can produce tornadoes with little or no advance warning. Some NWS offices advise treating a severe thunderstorm warning the same way you would treat a tornado warning. If a tornado warning is issued for your area, follow it right away.
What to do during a severe thunderstorm warning
- Go inside a sturdy building. Sheds and storage buildings are not safe.
- Leave mobile homes, which can blow over in high winds.
- Stay away from windows. At school or work, avoid large open rooms like gyms, cafeterias, and auditoriums.
- Stay away from electrical equipment and plumbing.
- Bring pets inside if there is time.
- Do not shelter under a tree. It could fall on you, and it raises your risk of being struck by lightning.
- If you are driving, a vehicle is safer than being outside, but drive to a sturdy shelter if you have time.
- If a tornado is spotted, go to the lowest floor and put as many walls as you can between you and the outside.
If you can hear thunder, you are close enough to be struck by lightning. See lightning safety for what to do.
See where warnings are now on the severe thunderstorm warnings page.