Wednesday, November 28, 2007

News: Great article at LAFD Blog - Fire weather, Red Flags and Burn Index

The Science Behind LAFD Fire Weather

By Brian Humphrey, Spokesman Los Angeles Fire Department
Original article at: LAFD Blog -
The Science Behind LAFD Fire Weather

How are decisions made by the Los Angeles Fire Department to pre-deploy resources on days of high wildfire hazard?

The answer is science.

The LAFD utilizes a Burning Index (BI) as the basis to determine the Department’s commitment to pre-deploy resources. A number of procedures occur daily to determine the actual BI:

First, fuel moisture readings are taken at Fire Station 108 on Mulholland Drive and communicated to the Division 3 office located at Fire Station 88 in the San Fernando Valley.

These fuel moisture readings are matched with predicted fire weather information (i.e. high/low temperatures, humidity, wind speed and direction) provided by a group of federal meteorologists that specialize in fire weather predictions at the Fire Weather Center (FWC), in Riverside California. This inter-agency group composed of California Department of Forestry & Fire Protection, Bureau of Land Management, the Forest Service and the California Governor's Office of Emergency Services provides the information to determine the LAFD Fire Rating and pre-deployment of resources.

LAFD Division 3 also conducts real time weather surveys throughout the San Fernando Valley to determine existing weather conditions. In addition, the National Weather Service web site is used to monitor fire weather conditions in and around the City of Los Angeles.

The National Weather Service information may be different from the weather information provided by the Fire Weather Center. National Weather Service information may indicate a Red Flag Warning, where weather information from FWC will indicate a lesser rating i.e. Extreme or Very High rating.

When the National Weather Service and FWC weather information do not match, the importance of real time weather surveys gain importance when considering pre-deployment of resources.

Real time weather surveys and long-term weather predictions are considered to be a better predictor of weather conditions for the City of Los Angeles. However, this does not preclude the possibility of Red Flag Warning conditions in other areas of Los Angeles County.

The BI-levels stated as a numerical value are as follows:

BI 0 to 37 = Low
BI 38 to 47 = Moderate
BI 48 to 110 = High
BI 111 to 161 = Very High
BI 162 to 211 = Extreme
BI 212 and above = Critical

Red Flag Alert days occur simply when the wind speed is 25 miles per hour or more and the relative humidity is 15% or less.

A red flag warning means that critical fire weather conditions are either occurring now... or will shortly. History has proven that a combination of strong winds, low relative humidity and warm temperatures will create explosive fire growth potential.

On Extreme, Critical and Red Flag Alert days the Fire Department pre-deploys resources.

The pre-deployment of resources into selected Neighborhood Fire Stations serving brush areas is proactive to address the increased brush fire potential. The specific stations/locations selected for pre-deployment are based on fire experience, area access, and fire potential.

To determine current Red Flag Parking Restrictions within the City of Los Angeles, please call 3-1-1 or visit:

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