Severe Thunderstorm Watch vs. Warning: What Makes a Storm Severe and Where to Shelter
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How we wrote this: A plain-English summary of National Weather Service severe thunderstorm safety pages, checked October 29, 2026.
What makes a thunderstorm "severe"
The NWS officially defines a severe thunderstorm as one capable of producing hail 1 inch or larger or wind gusts over 58 mph. Hail that size can damage roofs, cars and plants, and winds that strong can break large branches or knock trees over. Some severe storms produce hail larger than softballs or winds over 100 mph.
Lightning isn't part of the definition. Every thunderstorm has lightning, so the lightning safety rules apply even when no warning is issued.
Watch vs. warning
| Alert | NWS meaning | Area |
|---|---|---|
| Severe Thunderstorm Watch (Be prepared) | Severe storms are possible in and near the watch area. Stay informed and be ready to act | Large: many counties or even several states |
| Severe Thunderstorm Warning (Take action) | Severe weather has been reported by spotters or indicated by radar. Imminent danger to life and property | Small: about the size of a city or small county |
During a warning, the NWS says to take shelter in a substantial building and get out of mobile homes, which can blow over in high winds.
Where to go (NWS)
- At home: go to your secure location as soon as a warning is issued, and bring pets if there's time.
- At work or school: stay away from windows, and avoid large open rooms such as cafeterias, gyms and auditoriums.
- Outside: get inside a sturdy building immediately. Sheds and storage buildings aren't safe, and sheltering under a tree can be deadly, both from falling limbs and from lightning.
- In a vehicle: safer than being outside, but drive to the closest secure shelter if there's time.
Keep a NOAA Weather Radio or local news on, and make sure Wireless Emergency Alerts are turned on. Heavy downpours can also cause flash flooding. See flood safety. Also see cloud types.