How Tornado Warnings Are Issued — Radar, Spotters, and the NWS Decision
Who issues tornado warnings and how do they decide?
Tornado warnings are issued by meteorologists at the 122 local National Weather Service forecast offices, each covering its own patch of the country. The warning decision rests on two evidence streams: Doppler radar — which reveals a storm's rotation through velocity data and, since the dual-polarization upgrade, can even detect lofted debris — and ground truth from trained storm spotters, law enforcement, and the public. When a forecaster judges a tornado is occurring or imminent, they draw a polygon covering the storm's projected path, and the warning transmits within seconds to Wireless Emergency Alerts, NOAA Weather Radio, the Emergency Alert System, and every weather app and service downstream.
Who actually pulls the trigger?
Not a national center — the local office. The Storm Prediction Center in Norman, Oklahoma handles the multi-hour scale (outlooks and watches), but the tornado warning is issued by the NWS Weather Forecast Office responsible for that county — one of 122 across the country. During a severe weather event, that office staffs dedicated radar operators, each "working" specific storms scan by scan.
This locality matters: the warning forecaster knows the area's radar blind spots, terrain, and storm climatology, and they're on the phone with local spotters and emergency managers as they decide.
What does radar show the forecaster?
WSR-88D Doppler radar gives the forecaster three critical views, updating roughly every 1 to 6 minutes depending on scan strategy:
- Reflectivity — where precipitation is and how intense, revealing storm structure like the hook echo that wraps around a mesocyclone.
- Velocity — motion toward or away from the radar. A tight couplet of strong inbound wind next to strong outbound wind marks rotation; when it's small and intense at low altitude, a tornado may be forming or ongoing.
- Dual-polarization products — since the 2010s upgrade, radar can distinguish rain and hail from lofted debris. A Tornado Debris Signature is physical proof a tornado is on the ground doing damage, even in darkness or rain.
Most tornado warnings are issued on velocity signatures before any tornado is confirmed — that's where lead time comes from. "Radar-indicated" in a warning means exactly this.
Where do spotters fit in?
Radar has a physical blind spot: the beam travels in a straight line while the Earth curves away beneath it, so at long range the radar only sees a storm's middle and upper levels. What's happening at the ground — where the tornado is — must be observed by people. The NWS trains volunteer SKYWARN storm spotters (hundreds of thousands nationwide) to observe and report wall clouds, funnels, and tornadoes with precise locations.
A credible spotter report upgrades a warning's language from "radar-indicated" to "confirmed," often triggers immediate re-issuance with stronger wording, and feeds the escalation ladder toward PDS and Tornado Emergency tiers. At night or in rain-wrapped storms, when spotters can't see, dual-pol debris detection partially fills the gap — one reason nocturnal tornadoes remain the hardest warning problem.
What is the polygon, and why did county warnings go away?
Since October 2007, tornado warnings are storm-based polygons: a quadrilateral drawn around the tornado's current position and projected path over the warning's life, typically 30-60 minutes. Before that, warnings covered whole counties, alerting many people who were never in the path.
The polygon is why modern alerting can be precise — WEA targets phones inside it, and VORTEX checks your actual coordinates against the polygon (not just your county) before placing a phone call. It's also why two houses a mile apart can have different alert experiences: one is inside the drawn path, one isn't. Sirens and NOAA Weather Radio still activate on county logic in most places, which is the main source of "why did the siren go off for a storm across the county" confusion.
What happens in the seconds after issuance?
The forecaster's software (AWIPS) transmits the warning simultaneously to every dissemination path: NOAA's satellite and wire systems, NOAA Weather Radio transmitters (tone alarm + voice), FEMA's IPAWS gateway (which drives WEA and the broadcast Emergency Alert System), the public NWS API, and from there every weather app, TV station, and alert service. VORTEX ingests the NWS feed continuously, matches each new warning's polygon against subscriber locations every minute, and places phone calls for tornado and flash flood warnings that cover them.
Warnings are living products: the office issues follow-up statements as the storm moves, can extend, upgrade (damage threat tags), cancel early, or let the warning expire. Stay sheltered until your location is clear of the warning — not just until the noise stops. Sheltering guidance: weather.gov/safety/tornado.