The Storm Prediction Center’s Fire Weather Outlooks are intended to delineate areas where pre-existing fuel conditions, combined with forecast weather conditions during the next 2 days, will result in a significant threat for the ignition and/or spread of wildfires.

Each outlook consists of a categorical forecast that graphically depicts fire weather risk areas across the continental United States. Through various labels and colors on the graphic, the five types of Fire Weather Outlook risk areas are:

  • ELEVATED  – Elevated risk from wind and relative humidity
  • CRITICAL – Critical risk from wind and relative humidity
  • EXTREME – Extremely Critical risk from wind and relative humidity
  • ISO DRY T-STORMS – Elevated risk from dry thunderstorms
  • SCT DRY T-STORMS  – Critical risk from dry thunderstorms

The guidelines for the issuance of Critical and Extremely Critical Areas are provided below:

Critical for dry thunderstorms:

  • Dry fuels (as defined below)
  • At least 40% coverage (scattered) of cloud-to-ground lightning strikes with rainfall accumulation at or below 0.10″
  • Relative humidity at or below 15%
  • Temperatures at or above 50 or 60°F, depending on the season

Critical for wind and relative humidity:

  • Dry fuels (as defined below)
  • Sustained winds 20 mph or greater (15 mph Florida)
  • Relative humidity at or below 15%
  • Temperatures at or above 50 to 60°F, depending on the season
  • Concurrency of the above criteria for 3 hours or more

Extremely Critical for wind and relative humidity:

  • Very dry fuels (as defined below)
  • Sustained winds 30 mph or greater (25 mph Florida)
  • Relative humidity at or below 10%
  • Temperatures at or above 60 or 70°F, depending on the season
  • Concurrency of the above criteria for 3 hours or more
  • NOTE: Extremely critical delineations are made when wind, relative humidity and temperatures significantly deviate from climatological normals, but can be made for borderline weather conditions where exceptional drought exists.

Dry Fuel guidelines: The Storm Prediction Center utilizes fuel dryness level grids produced by Geographic Area Coordination Centers (GACCs). Fuel dryness levels of dry or very dry are necessary for the issuance of any type of SPC fire weather outlook area. When GACC dryness level grids are not available, SPC considers fuels to be dry where there is a National Fire Danger Rating System Adjective Class Rating of at least High, or 100/1000-hr dead fuel moisture below 10 percent, or at least active severe drought.

If an area is being considered for a possible Critical area but there is low confidence, or the expected weather conditions will be just below the aforementioned criteria for a Critical area, an Elevated area is highlighted. Where Critical areas are highlighted, an Elevated area will surround the Critical area. Guidelines for an Elevated area are provided below:

Elevated for dry thunderstorms, or wind and relative humidity:

  • 10-39% coverage (isolated) of cloud-to-ground lightning strikes with rainfall accumulation at or below 0.10″ over dry fuels OR
  • A combination of sustained wind speeds of 15 mph or greater, relative humidity up to 20%, and temperatures at or above 45 or 55°F (depending on the season), for a duration of 3 hours or more over dry fuels OR
  • Brief (duration of less than 3 hours) and/or localized exceedance of critical thresholds over dry fuels OR
  • Critical conditions occurring with marginal fuel dryness

This information is adapted specifically for Colorado and sourced directly from the Storm Prediction Center’s website. You can find the original version here.