Severe thunderstorm watch vs warning: what is the difference?

01

What is a severe thunderstorm watch?[1]

A watch means the atmosphere is favorable for severe thunderstorms across a broad region, typically covering many counties for several hours. Nothing has necessarily happened yet. It is the signal to review your plans and stay aware.

Watches are issued well in advance and cover large areas because the ingredients for severe weather can be identified before individual storms form. The forecast can be confident that the region is primed without knowing which towns will be hit.

The practical response is preparation rather than action: bring in loose outdoor items, charge devices, know where you would shelter, and decide now whether afternoon plans in exposed places are still sensible.

02

What is a severe thunderstorm warning?[1]

A warning means a severe storm has been detected by radar or reported by a spotter, and it threatens a specific area within roughly the next hour. In the US, severe means hail of at least one inch or winds of at least 58 mph.

Warnings cover much smaller areas than watches, often the path of a single storm through a few counties, and last well under an hour. The tighter scope reflects that the storm is real and its track is known rather than hypothesised.

Notably, lightning is not part of the severe criteria. A storm producing constant cloud-to-ground lightning without large hail or damaging wind will never be warned as severe, which does not make its lightning less dangerous.

03

Why is lightning not a warning criterion?[2][1]

Because every thunderstorm produces lightning by definition, so it cannot distinguish a severe storm from an ordinary one. Warnings flag the unusual hazards. Lightning is treated as a constant risk present in all thunderstorms.

This trips people up, because a storm without a warning can feel officially safe. It is not. The absence of a severe warning tells you the hail and wind thresholds are not expected to be met, and nothing at all about strike risk.

That is the whole justification for the thunder rule existing separately from the warning system. Thunder is the universal, local, immediate signal, and it does not require anyone to issue anything.

04

What should you do at each stage?[2]

On a watch, prepare and stay informed. On a warning, move indoors to a substantial building and stay away from windows. On thunder, regardless of either, go inside and start the 30-minute clock from the last rumble.