Red flag warning

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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.

[edit] Example of a Red Flag Warning

RED FLAG WARNING
NATIONAL WEATHER SERVICE BISMARCK ND
1110 AM CDT SAT MAY 3 2008

...RED FLAG WARNING IN EFFECT FOR PORTIONS OF NORTHERN AND CENTRAL
NORTH DAKOTA THIS AFTERNOON AND EARLY EVENING FOR STRONG WINDS AND
LOW RELATIVE HUMIDITIES...

.MINIMUM HUMIDITIES WILL RANGE FROM 12 TO 18 PERCENT THIS AFTERNOON
ALONG WITH NORTHWEST WINDS OF 15 TO 25 MPH. RANGELAND FIRE DANGER
INDICES WILL REMAIN IN THE VERY HIGH CATEGORY. THE COMBINATION OF
THE STRONG WINDS...LOW RELATIVE HUMIDITY...AND VERY HIGH RANGELAND
FIRE DANGER INDICES WILL CREATE CRITICAL FIRE WEATHER BEHAVIOR THIS
AFTERNOON INTO THE EARLY EVENING HOURS. THUS A RED FLAG WARNING HAS
BEEN ISSUED. WINDS WILL QUICKLY SUBSIDE BY SUNSET AND HUMIDITIES
WILL BEGIN TO RECOVER ABOVE 20 PERCENT.

NDZ002>005-010>013-018>023-025-035>037-040200-
/O.NEW.KBIS.FW.W.0018.080503T1800Z-080504T0200Z/
BURKE-RENVILLE-BOTTINEAU-ROLETTE-MOUNTRAIL-WARD-MCHENRY-PIERCE-
DUNN-MERCER-OLIVER-MCLEAN-SHERIDAN-WELLS-FOSTER-BURLEIGH-KIDDER-
STUTSMAN-
1110 AM CDT SAT MAY 3 2008 /1010 AM MDT SAT MAY 3 2008/

...RED FLAG WARNING IN EFFECT UNTIL 9 PM CDT /8 PM MDT/ THIS
EVENING...

THE NATIONAL WEATHER SERVICE IN BISMARCK HAS ISSUED A RED FLAG
WARNING...WHICH IS IN EFFECT UNTIL 9 PM CDT /8 PM MDT/ THIS
EVENING.

MINIMUM HUMIDITIES WILL RANGE FROM 12 TO 18 PERCENT THIS AFTERNOON
ALONG WITH NORTHWEST WINDS OF 15 TO 25 MPH. RANGELAND FIRE DANGER
INDICES WILL REMAIN IN THE VERY HIGH CATEGORY. THE COMBINATION OF
THE STRONG WINDS...LOW RELATIVE HUMIDITY...AND VERY HIGH RANGELAND
FIRE DANGER INDICES WILL CREATE CRITICAL FIRE WEATHER BEHAVIOR THIS
AFTERNOON INTO THE EARLY EVENING HOURS. THUS A RED FLAG WARNING HAS
BEEN ISSUED. WINDS WILL QUICKLY SUBSIDE BY SUNSET AND HUMIDITIES
WILL BEGIN TO RECOVER ABOVE 20 PERCENT.

A RED FLAG WARNING MEANS THAT CRITICAL FIRE WEATHER CONDITIONS
ARE EITHER OCCURRING NOW...OR WILL SHORTLY. A COMBINATION OF
STRONG WINDS...LOW RELATIVE HUMIDITY...AND WARM TEMPERATURES WILL
CREATE EXPLOSIVE FIRE GROWTH POTENTIAL.

$$

KS