Red flag warning
Encyclopedia
A Red Flag Warning is a forecast warning issued by the United States
National Weather Service
to inform area firefighting and land management agencies that conditions are ideal for wildland fire ignition and propagation. After drought conditions, and when humidity
is very low, and especially when high or erratic winds which may include lightning are a factor, the Red Flag Warning becomes a critical statement for firefighting agencies, which 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 varies with each Weather Service Office’s warning area based on the local vegetation type, topography
, and distance from major water sources but usually includes 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.
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. That watch then remains in effect until it expires, is canceled, or upgraded to a Red Flag Warning.
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
National Weather Service
National Weather Service
The National Weather Service , once known as the Weather Bureau, is one of the six scientific agencies that make up the National Oceanic and Atmospheric Administration of the United States government...
to inform area firefighting and land management agencies that conditions are ideal for wildland fire ignition and propagation. After drought conditions, and when humidity
Humidity
Humidity is a term for the amount of water vapor in the air, and can refer to any one of several measurements of humidity. Formally, humid air is not "moist air" but a mixture of water vapor and other constituents of air, and humidity is defined in terms of the water content of this mixture,...
is very low, and especially when high or erratic winds which may include lightning are a factor, the Red Flag Warning becomes a critical statement for firefighting agencies, which 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 varies with each Weather Service Office’s warning area based on the local vegetation type, topography
Topography
Topography is the study of Earth's surface shape and features or those ofplanets, moons, and asteroids...
, and distance from major water sources but usually includes 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.
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. That watch then remains in effect until it expires, is canceled, or upgraded to a Red Flag Warning.
Example of a Red Flag Warning
URGENT - FIRE WEATHER MESSAGE
NATIONAL WEATHER SERVICE SEATTLE WA
348 PM PDT SAT JUL 25 2009
...ONE OF THE MOST CRITICAL FIRE WEATHER SETUPS IN YEARS FOR
WESTERN WASHINGTON...
.AN UPPER LEVEL LOW PRESSURE CENTER CONTINUES TO SPIN OVER
CENTRAL WASHINGTON THIS AFTERNOON.
WAZ653-654-656>659-661-662-261200-
/O.CON.KSEW.FW.W.0003.000000T0000Z-090726T1200Z/
STRAIT OF JUAN DE FUCA AND NORTHWEST INTERIOR LOWLANDS-
CENTRAL AND SOUTH PUGET SOUND LOWLANDS-
WEST SLOPES OF THE NORTH CASCADES-
WEST SLOPES OF THE CENTRAL CASCADES-NORTH CASCADES-
CENTRAL CASCADES-EAST PORTION OF THE OLYMPIC MOUNTAINS-
EAST PORTION OF NORTH CASCADES NATIONAL PARK/LAKE CHELAN NATIONAL
RECREATIONAL AREA-
348 PM PDT SAT JUL 25 2009
...RED FLAG WARNING REMAINS IN EFFECT UNTIL 5 AM PDT SUNDAY...
A RED FLAG WARNING REMAINS IN EFFECT UNTIL 5 AM PDT SUNDAY.
AN UPPER LEVEL LOW PRESSURE CENTER CONTINUED TO SPIN OVER CENTRAL
WASHINGTON ON SATURDAY AFTERNOON. THUNDERSTORMS HAD ALREADY
DEVELOPED OVER SOUTHERN BRITISH COLUMBIA AND WILL MOVE SOUTHWEST
INTO WESTERN WASHINGTON LATER THIS AFTERNOON AND TONIGHT AS THEY
TRACK AROUND THE PERIPHERY OF THE UPPER LOW. THE STORMS WILL
FIRST REACH THE NORTH CASCADES AND NORTH INTERIOR...THEN SPREAD
SOUTHWEST AND SOUTH THIS EVENING THROUGH THE CENTRAL CASCADES AND
THE PUGET SOUND LOWLANDS. THUNDERSTORMS COULD ALSO CLIP THE EAST
SLOPES OF THE OLYMPIC MOUNTAINS.
SOME OF THESE THUNDERSTORMS ARE EXPECTED TO BE UNUSUALLY PROLIFIC
LIGHTNING PRODUCERS. GIVEN THE EXPECTED ABUNDANCE OF LIGHTNING
AND CRITICALLY DRY FUEL STATES...MULTIPLE FIRE IGNITIONS ARE
EXPECTED.
ONE THING THAT MAKES THIS ROUND OF LIGHTNING SO CRITICAL IS THAT
IT WILL BE FOLLOWED UP ON SUNDAY AND MONDAY BY A BUILDING AND
PROLONGED HEAT WAVE. UNLIKE WESTERN WASHINGTON`S TYPICAL
LIGHTNING PATTERN IN WHICH LIGHTNING IS FOLLOWED BY COOL MARINE
AIR...THIS LIGHTNING PATTERN WILL BE FOLLOWED INSTEAD BY
HOT...DRY AND INCREASINGLY UNSTABLE WEATHER ON SUNDAY...MONDAY
AND TUESDAY. THIS WILL MAKE HOLDOVER AND SLEEPER FIRES A GREAT
CONCERN IN THE DAYS TO COME.
PLEASE RELAY THIS MESSAGE TO FIRE AND ENGINE CREWS IN THE FIELD.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
PEOPLE WHO WILL BE OUTDOORS FROM THIS AFTERNOON THROUGH TONIGHT
SHOULD BE AWARE OF THE LIGHTNING THREAT AND THE ENHANCED THREAT
OF WILDFIRES. MAKE AN EXTRA EFFORT TO FULLY EXTINGUISH CAMPFIRES
AND REPORT ANY NEW WILDFIRES WHICH YOU MIGHT SEE. FIREFIGHTING
AGENCIES SHOULD BE READY FOR SEVERAL BUSY DAYS OF INITIAL ATTACK.
A RED FLAG WARNING IS ISSUED WHEN DRY LIGHTNING OR THE
COMBINATION OF STRONG WINDS AND LOW HUMIDITIES ARE IMMINENT OR
OCCURRING.
&&
$$
HANER
WEATHER.GOV/SEATTLE
External links
- Fire weather forecasts (Storm Prediction CenterStorm Prediction CenterThe Storm Prediction Center , located in Norman, Oklahoma, is tasked with forecasting the risk of severe thunderstorms and tornadoes in the contiguous United States. The agency issues convective outlooks, mesoscale discussions, and watches as a part of this process...
)