Fire weather describes a specific set of atmospheric conditions—including high heat, low relative humidity, strong or erratic winds, and atmospheric instability—that dramatically increases the likelihood of wildfire ignition and the speed at which a fire spreads. This term is standard usage among major agencies like the U.S. National Weather Service (NWS), the National Wildfire Coordinating Group (NWCG), and Natural Resources Canada, with forecasts ranging from same-day tactical alerts to multi-day outlooks. The primary meteorological drivers are low humidity and strong winds, which dry out fast-burning fuels like grass and leaf litter, alongside antecedent drought and "dry lightning" strikes that ignite fires without the benefit of suppressing rainfall. To convey specific dangers, the NWS Storm Prediction Center issues categorical updates (Elevated, Critical, or Extremely Critical), while local offices issue urgent Red Flag Warnings with thresholds tailored to regional climates—for instance, Boulder, Colorado requires wind gusts of 25 mph or greater and humidity at or below 15%. To standardize the danger, experts rely on quantitative indices such as the National Fire Danger Rating System's Spread, Energy Release, and Ignition components, as well as the Fosberg Fire Weather Index developed by USDA researcher Michael A. Fosberg.