A red flag warning is a forecast warning issued by the

National Weather Service The National Weather Service (NWS) is an agency of the United States federal government that is tasked with providing weather forecasts, warnings of hazardous weather, and other weather-related products to organizations and the public for the ...

in the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...

to inform the public, firefighters, and land management agencies that conditions are ideal for wildland fire combustion, and rapid spread. After drought conditions, when

humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity dep ...

is very low, and especially when there are high or erratic winds which may include lightning as a factor, the Red Flag Warning becomes a critical statement for firefighting agencies. These agencies often alter their staffing and equipment resources dramatically to accommodate the forecast risk. To the public, a Red Flag Warning means high fire danger with increased probability of a quickly spreading vegetation fire in the area within 24 hours. The weather criteria for fire weather watches and red flag warnings vary with each Weather Service office’s warning area based on the local vegetation type,

topography Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the land forms and features themselves, or a description or depiction in maps. Topography is a field of geoscience and planetary sc ...

, and distance from major water sources. They usually include the daily vegetation moisture content calculations, expected afternoon high temperature, afternoon minimum relative humidity and daytime wind speed. Outdoor burning bans may also be proclaimed by local law and fire agencies based on red flag warnings. In October 2019, the National Weather Service introduced an enhanced version of the warning, called extreme red flag warning. Analogous to the particularly dangerous situation (PDS) wording on a high-end severe weather watch, this means that conditions for fire growth and behavior are extremely dangerous due to a combination of strong winds, very low humidity, long duration, and very dry fuels. It was used for the first time on October 29, 2019. A separate but less imminent forecast may include a fire weather watch, which is issued to alert fire and land management agencies to the possibility that Red Flag conditions may exist beyond the first forecast period (12 hours). The watch is issued generally 12 to 48 hours in advance of the expected conditions, but can be issued up to 72 hours in advance if the NWS agency is reasonably confident. The term “Fire Weather Watch” is headlined in the routine forecast and issued as a product, similar to the other primary fire warning terms. That watch then remains in effect until it expires, is canceled, or upgraded to a red flag warning.

External links

Fire weather forecasts
(

Storm Prediction Center The Storm Prediction Center (SPC) is a US government agency that is part of the National Centers for Environmental Prediction (NCEP), operating under the control of the National Weather Service (NWS), which in turn is part of the National Oceani ...

)

References

{{SevWea nav, state=collapsed Fire prevention Weather warnings and advisories Wildfire suppression National Weather Service

See also

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References