Red Flag Warning Days
What is a Red Flag Warning?
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. It is critical that every person consider their actions in relation to the probability of a wildfire. Early notification is critical to responding agencies - report problems as soon as you are made aware of them. Most importantly, have a family evacuation plan in place. If given only 5 minutes to evacuate your home, consider in advance what items you would take with you.
The North Tahoe Fire Protection District is busy preparing for the possibility of a wildfire within our area. NTFPD personnel are proactive in anticipating these events when the weather forecast indications are present. Our crews will be out on patrol in the neighborhoods during Red Flag Warning days and there will be signs indicating Red Flag Warning days in front of our fire stations as well as magnetic signs on all of our fire apparatus and command vehicles.
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.
Here is some additional information on how the Red Flag Warning days (RFW) are determined by the National Weather Service.
The National Weather Service (NWS) offices issue Fire Weather Watches and Red Flag Warnings for critical fire weather patterns that contribute to extreme fire danger and/or fire behavior.
A Fire Weather Watch is used to alert agencies to the high potential for development of a Red Flag event in the 12-72 hour time frame. The Watch may be issued for all or selected portions of a fire weather zone or zones. A watch may be issued in the first 12 hour time period only for an expected dry thunderstorm event.
Wind and Humidity - Wind and humidity criteria are geared toward those situations which may result in rapid spread of wildfires. Because topography and vegetation play a big role in this, several sets of criteria are used across California. Where possible, issuance criteria have been meshed with those used in adjacent states to meet the needs of agencies whose jurisdictions cross state lines. Criteria are listed in the Wind/Humidity Table (see below).
Red Flag warning/fire weather watches in discussions and headlines - In the discussion portion of the Fire Weather Planning Forecast (FWF), NWS offices will mention critical weather patterns that might lead to conditions approaching or exceeding Red Flag criteria through the extended forecast. This will assist fire agencies in their allocating and moving resources in anticipation of increased fire activity. Fire Weather Watches and Red Flag Warnings will be headlined in spot forecasts, the fire weather narrative, and appropriate zone sections within the fire weather planning forecast. The headline will be in the same format as on the RFW product itself.
Collaboration with agencies - Fire Weather Watches and Red Flag Warnings normally will be issued only after conferring with the affected agencies or a representative subset of affected agencies, to include the Redding and Riverside Predictive Services Units. This will allow for input on fuel conditions and local concerns. However, the ultimate responsibility for the issuance of a watch/warning rests with the NWS forecaster.
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Northern California East of Cascade/Sierra Crest and Western Great Basin including the Modoc Plateau |
214, 270-273, 278, 284, 285
272 is the zone for the Lake Tahoe Area |
Tahoe Management Basin: Three hours of wind gusts > 30 mph and Relative Humidity < 20% |
Rest: Three hours of wind gusts > 30 mph and Relative Humidity <15%. |
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Tuesday, September 07, 2010
