A Fire Weather Outlook is a Storm Prediction Center (SPC) forecast that outlines areas of the continental United States where existing fuel conditions and forecast weather combine into a significant threat for wildfires to start or spread. SPC issues them for Day 1, Day 2 and Days 3 to 8, each as a categorical map with a written discussion.
Two kinds of fire weather threat
The outlook tracks two separate threats. One is the wind and low humidity threat, ranked Elevated, Critical and Extremely Critical.
The other is the dry thunderstorm threat, where lightning reaches the ground with little rain. SPC labels these areas Isolated Dry Thunderstorms or Scattered Dry Thunderstorms.
Days 1 and 2 versus Days 3 to 8
The Day 1 and Day 2 outlooks draw categorical areas, and each is updated once during the day. The Day 3 to 8 outlook goes out each afternoon and has both a categorical and a probabilistic part.
In the Day 3 to 8 product, forecasters use 40 and 70 percent probabilities for Critical fire weather, and 10 and 40 percent for dry thunderstorms. The map service splits each of those days into a winds and low humidity layer and a dry thunderstorm layer.
Who it is for
Under NWS Instruction 10-401, the outlooks serve as guidance for local NWS forecasters and help land management agencies judge large-scale areas of fire danger. The text discussion explains which weather and fuel factors drove the areas, which is often more useful than the shading alone.
What the outlook does not tell you
An outlook area is not a Red Flag Warning. Local offices issue Fire Weather Watches and Red Flag Warnings against criteria worked out with their own land management partners, so an outlook area and a local warning will not always match.
The outlook also does not predict where a fire will start. It describes how readily a fire could start or spread across a broad region if one does.