Red flag warning

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A red flag warning is a forecast warning issued by the National Weather Service in the United States to inform the public, firefighters, and land management agencies that conditions are ideal for wildland fire combustion, and rapid spread.[1] After drought conditions, when humidity 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, 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.[2]

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.[3] That watch then remains in effect until it expires, is canceled, or upgraded to a red flag warning.

Examples[edit]

Red flag warning[edit]

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 SEVERE 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

PDS Red flag warning[edit]

URGENT - FIRE WEATHER MESSAGE
National Weather Service Salt Lake City UT
1129 AM MDT Sun Sep 15 2019

UTZ478-492-495-161200-
/O.CON.KSLC.FW.W.0020.190916T0200Z-190917T1000Z/
Salt Lake Desert-Central Utah West Desert-
Color Country West Desert-
1129 AM MDT Sun Sep 15 2019

...RED FLAG WARNING REMAINS IN EFFECT FROM 8 PM THIS EVENING TO
4 AM MDT TUESDAY FOR WIND AND LOW RELATIVE HUMIDITY FOR FIRE
WEATHER ZONES 478...492 AND 495...

...THIS IS A PARTICULARLY DANGEROUS SITUATION...

* AFFECTED AREA...Fire Weather Zone 478 Salt Lake Desert...Fire
  Weather Zone 492 Central Utah West Desert and Fire Weather
  Zone 495 Color Country West Desert.

* WINDS...Increasingly gusty this evening and tonight from the
  South gusting 30 to 40 mph. Winds peak tomorrow afternoon and
  evening with gusts of 35 to 55 mph, before gradually
  decreasing after a wind switch to the northwest Monday night
  with gusts of 25 to 45 mph. Some locations in the West Desert
  may continue to gust 60 mph or greater Monday night.

* RELATIVE HUMIDITY...Poor RH recovery tonight after reaching
  single digits earlier during the day. RH drops to between 8-15%
  Monday, rising Monday night with the frontal passage.

* IMPACTS...This is a particularly dangerous situation due to the
  strength of the winds. Hot dry and windy conditions will
  combine to support rapid spread of fires.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A Red Flag Warning means that critical fire weather conditions
are either occurring now...or are imminent. A combination of
strong winds...low relative humidity...and warm temperatures can
contribute to extreme fire behavior.

&&

$$

Extreme red flag warning[edit]

URGENT - FIRE WEATHER MESSAGE
National Weather Service Los Angeles/Oxnard CA
355 PM PDT Tue Oct 29 2019

...EXTREME RED FLAG WARNING IN EFFECT FROM 11 PM TUESDAY THROUGH
6 PM THURSDAY PDT FOR MUCH OF LOS ANGELES AND VENTURA COUNTIES
DUE TO STRONG NORTHEAST WINDS AND VERY LOW HUMIDITIES...

.A strong Santa Ana wind event is expected tonight through
Thursday, and could be one of the strongest of recent memory.
Damaging wind gusts between 50 and 70 mph are expected over most
of Los Angeles and Ventura Counties, with isolated gusts to
around 80 mph likely. Although the air is cold, humidities will
lower to the single digits nearly everywhere by Wednesday or
Thursday, and down to 1 or 2 percent in the driest windiest
locations. Overnight recoveries Wednesday night will be near
zero. This all adds up to an extreme fire weather threat, meaning
that conditions are as dangerous for fire growth and behavior as
we have seen in recent memory. Use extreme caution with any
potential ignition sources, and residents in high fire risk areas
should be ready and set to evacuate if emergency officials say so.

CAZ244>246-253-254-288-301800-
/O.CON.KLOX.FW.W.0006.191030T0600Z-191101T0100Z/
Ventura County Interior Valleys-Ventura County Coastal Valleys-
Santa Monica Mountains Recreational Area-
Ventura County Mountains / Los Padres National Forest-
Los Angeles County Mountains / Angeles National Forest-
Santa Clarita Valley-
355 PM PDT Tue Oct 29 2019

...RED FLAG WARNING REMAINS IN EFFECT FROM 11 PM THIS EVENING TO
6 PM PDT THURSDAY FOR STRONG WINDS AND VERY LOW HUMIDITY OVER THE
MOUNTAINS OF LOS ANGELES AND VENTURA COUNTIES AND THE VENTURA AND
SANTA CLARITA VALLEYS...

* Winds...Northeast 30 to 50 mph with gusts to 70 mph. Isolated
  gusts to 80 mph possible. Strongest on Wednesday.

* Relative Humidity...As low as 1 to 5 percent. Very poor to no
  overnight recoveries.

* Impacts...If fire ignition occurs, conditions will be
  favorable for extreme fire behavior, long range spotting, and
  very rapid fire spread which would threaten life and property.
  The strength of the expected winds could result in downed
  trees and power lines as well as power outages.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

An extreme Red Flag Warning means that conditions are as
dangerous for fire growth and behavior as we have seen in recent
memory, due to the combination of strong winds, very low
humidity, long duration, and very dry fuels. Use extreme caution
with potential fire ignition sources. Residents in high fire risk
areas should be ready and set to evacuate if emergency officials
say so.

&&

See also[edit]

External links[edit]

References[edit]

  1. ^ "Red Flag Warning". National Weather Service. 2015-03-05. Retrieved 2018-05-02.
  2. ^ ‘Extreme’ warning issued ahead of hurricane-force Santa Ana winds, the strongest since 2007
  3. ^ "Three Wildfire Terms You Should Know". www.cleanairresources.com. 2019-02-24. Retrieved 2019-03-07.