Severe Thunderstorm Warning — What It Means and When to Take It Seriously
What does a severe thunderstorm warning mean?
A severe thunderstorm warning means a storm producing winds of 58 mph or greater and/or hail one inch (quarter size) or larger is occurring or imminent in the warned polygon — take shelter indoors. Since 2021, each warning carries a damage-threat tag: base (58+ mph / 1"+ hail), considerable (70+ mph / 1.75"+ hail), or destructive (80+ mph / 2.75"+ hail) — and destructive-tagged warnings trigger Wireless Emergency Alerts, the same phone-buzzing channel as tornado warnings. The category is widely underestimated: an 80 mph downburst delivers hurricane-force winds over a far larger area than most tornadoes, and squall lines under severe thunderstorm warnings can and do spin up tornadoes with little additional notice.
What triggers the warning?
The same evidence chain as tornado warnings — radar plus spotters, evaluated by the local NWS office. Radar signatures of damaging wind (bowing line segments, strong mid-level winds descending toward the surface) or large hail (extreme reflectivity depth, three-body scatter spikes) justify a warning before the first report; trained spotter and public reports of severe criteria — 58+ mph gusts or 1-inch hail — confirm and extend them. Warnings are storm-based polygons lasting 30-60 minutes, just like tornado warnings.
Note what does not trigger it: rain rates, lightning frequency, or storm appearance. A storm can be a torrential lightning barrage and never be "severe" by definition — and its flood risk is handled by separate flash flood products.
What are the damage-threat tiers?
In 2021 the NWS added damage-threat tags to convey that "severe" spans an enormous range:
- Base — 1.00"+ hail and/or 58+ mph winds. Roof, tree, and vehicle damage possible.
- Considerable — 1.75"+ (golf ball) hail and/or 70+ mph winds. Widespread tree damage, structural damage begins.
- Destructive — 2.75"+ (baseball) hail and/or 80+ mph winds. Hurricane-force winds or roof-penetrating hail; these warnings trigger WEA phone alerts automatically. Derechos and giant-hail supercells are the classic cases.
If your phone buzzes with a severe thunderstorm warning, that alone tells you it's the destructive tier — the NWS deliberately reserved the channel so the buzz means business.
Why shouldn't I shrug at a "regular" severe thunderstorm warning?
Three reasons, in escalating order. First, the base criteria already describe damaging weather — 58 mph winds snap limbs onto cars and power lines, and 1-inch hail cracks windshields and skylights. Second, warned storms escalate: the storm warned for wind at 6:10 can produce a 75 mph gust front at 6:25, and follow-up statements upgrade tags mid-warning. Third — the underappreciated one — squall lines under severe thunderstorm warnings produce tornadoes. QLCS spin-ups develop in minutes, sometimes too fast for a separate tornado warning; many carry only a "tornado possible" tag inside the severe thunderstorm warning. If a warned line is bearing down on you at night, being already-sheltered is what closes that gap.
What should I actually do during one?
The core action is simple: get inside a sturdy building and stay away from windows until the storm passes — wind-thrown debris and hail through glass are the primary injury mechanisms. Vehicles, porches, carports, and tents don't qualify. If the warning carries a considerable or destructive tag, treat it with tornado-grade seriousness: interior room, lowest floor. For complete guidance — including lightning safety, which applies to every thunderstorm, severe or not — use the National Weather Service's pages at weather.gov/safety/thunderstorm.
How do these warnings reach me?
Unevenly — and it's worth knowing the gaps. NOAA Weather Radio alarms for them and local broadcasters cover them, but WEA only fires for the destructive tier, most siren systems don't sound for them at all, and many app defaults bury them below tornado warnings. That leaves a real coverage hole for base and considerable warnings — the 70 mph gust that drops a tree on the car you were about to drive. A weather radio or an app with severe thunderstorm notifications enabled closes it. VORTEX surfaces every active severe thunderstorm polygon on the live map, and VORTEX Pro push notifications cover warned storms for your saved locations so the non-WEA tiers don't slip past you.