The National Weather Service issues alerts in three tiers, and the vocabulary is consistent across every hazard type, thunderstorm, tornado, flood, winter storm, hurricane, heat.
A watch is having the ingredients on the counter. A warning is the pan on fire.
Scale and timing differ too
Watches are issued for large areas, often many counties, hours in advance, a tornado watch might cover half a state for six hours. Warnings are small and short: a specific polygon, often a fraction of a county, valid for 30 to 60 minutes, issued when radar or a spotter confirms the threat.
That's why a warning demands immediate action. It isn't a forecast anymore; it's a report.
The ones worth knowing on sight
- Severe Thunderstorm Warning: winds of 58 mph or greater, or hail one inch or larger. Not a routine storm.
- Tornado Warning: rotation detected or a tornado sighted. Go to your safe place immediately.
- Flash Flood Warning: rapid flooding occurring or imminent. Never drive into water.
- Hurricane Watch / Warning: 48 and 36 hours before expected onset of tropical storm force winds, respectively. The warning arrives while conditions are still calm on purpose, because preparation must finish before the weather arrives.
- Special Weather Statement: a strong storm that hasn't met severe criteria. Worth reading.
Where they come from
122 local NWS forecast offices issue most warnings for their areas, while national centers handle specialized threats, the Storm Prediction Center for severe weather and tornado watches, the National Hurricane Center for tropical systems. All of it is public, free, and distributed within seconds through the same feeds any app can access.