Definition
A Severe Weather Warning (WW) is an unscheduled bulletin issued by the National Weather Service's Storm Prediction Center to alert that severe thunderstorms or tornadoes are occurring, or are highly likely to occur, within a defined area and time window. It defines the boundaries, valid period, and type of severe weather expected (severe thunderstorm or tornado).
Plain English
An urgent weather alert telling pilots that dangerous storms — severe thunderstorms or tornadoes — are happening or about to happen in a specific area for a specific period of time.
Context Anchor
Seen in weather briefings and instrument weather discussions when severe weather could affect a planned route or make continued flight unsafe.
Derivation
The 'WW' product code historically stood for 'Weather Watch' in National Weather Service usage, and over time came to label the bulletin itself. Knowing it is a watch-style product helps frame it: it warns of conditions favorable for severe weather across an area, rather than pinpointing a single storm cell.
Why Pilots Care
It directly affects route selection, altitude choice, and whether a flight can proceed safely.
Grounding Statement
If a WW covers your route, picture a marked area on the weather map that you plan around, not through.
Intuition Check
Do not read “warning” as “maybe later.” In this context, a warning means the dangerous weather is happening or expected soon in a specific area and time period.
Example Sentence 1
During the preflight briefing, the specialist mentioned an active WW covering most of the planned route until 2200Z, so the pilot delayed departure.
Example Sentence 2
Because of the WW, the flight was rerouted to avoid the affected area.