The Los Angeles Fire Department uses a Burning Index rating to determine the level of fire danger/threat to the area. They use a scale to assess the threat from 0 (low) to 162 and above (extreme).
The BI forecast for Wednesday into Thursday is 296 -- the highest number the fire chief has ever seen.
Below is an explanation of the Burning Index from LAFD:
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How are decisions made by the Los Angeles Fire Department to strategically place resources on days of high wildfire hazard? The answer is science.
The LAFD utilizes a Burning Index (BI) to determine the Department’s commitment to pre-deploy apparatus and personnel. A number of procedures occur each day to determine the BI in Los Angeles.
- First, dead vegetation fuel moisture readings are taken in the early afternoon at Fire Station 108 on Mulholland Drive near Coldwater Canyon, and communicated to LAFD's North Division Headquarters located at Fire Station 88 in the San Fernando Valley.
- Second, a group of federal meteorologists at the Southern California Geographic Area Coordination Center (SCGACC) in Riverside, California provide a "fire weather forecast" consisting of a predicted high temperature, low relative humidity, wind speed and direction for the next day.
- Third, historical data (high/low temperature, high/low relative humidity and hours of rainfall in the last 24 hours) is mixed into the brew.
All of this information is fed into equations that make up the National Fire Danger Rating System (NFDRS). The result is the BI. Theoretically, fire danger is elevated when BI’s reach high values. The daily BI level is stated as a numerical value:
BI 0 to 37 = Low
BI 38 to 47 = Moderate
BI 48 to 110 = High
BI 111 to 161 = Very High
BI 162 and above = Extreme
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On days of Extreme Fire Danger, your Los Angeles Fire Department may pre-deploy resources at select Neighborhood Fire Stations in-and-near areas prone to wildfire.
Not all forecasts become reality, so LAFD North Division staff conduct real-time weather surveys, monitor Remote Automated Weather Stations (RAWS) in and near the City of Los Angeles and consult the National Weather Service (NWS) to stay abreast of fire weather conditions and forecasts.
Please remember that radio and television weather reports are broadcast to a wider community than the City of Los Angeles, and pass along information on "Red Flag Warnings", for instance, that may *not* apply to the area served by the LAFD.
The NWS and SCGACC may come to different conclusions on the forecast as well, based on which computer model each agency trusts. Ultimately, the LAFD makes decisions on pre-deployment based on all of these inputs – with a lot of experience mixed in.
Kindly note that LAFD uses the term "Red Flag Alert" to indicate forecasted or existing "Red Flag" conditions inside the City of Los Angeles. A "Red Flag Alert" is called when the wind speed is 25 miles per hour or more and the relative humidity is 15% or less. History has proven that a combination of strong winds, low humidity and warm temperatures will create explosive fire growth potential.
For this reason, parking restrictions may exist on certain narrow streets in brush areas during “Red Flag Alert” conditions. To determine current Red Flag Alert Parking Restrictions within the City of Los Angeles, please call 3-1-1 or visit: http://lafd.org/redflag.