Fire Weather Discussion
The Chandler Burning Index (CBI) as seen above uses the air temperature and relative humidity to calculate a numerical index of fire danger.
That number is then equated to the Fire Danger severity of either extreme, very high, high, moderate, or low. It's based solely on weather
conditions, with no adjustment for fuel moisture. Here on the Oak Ridge Weather site, the CBI is calculated from the current weather conditions
and reflects the current calculated fire danger. The National Weather Service calculates a 30 day Chandler Burning Index based on forecasted
weather conditions for the month.
Click the link to the right to see the Chandler Burning Index Descriptioin
Fire danger is the probability of a fire to start, the rate of spread and intensity of its burn. This probability is influenced by fuel
type, fuel moisture, amount of fuel, and slope of the land area. Another important influence is weather, particularly wind and relative
When relative humidity is below 50%, prescribed burning during the summer does best. During the Spring or Fall Fire Season, a relative humidity below 40% can mean that any wildfires will be difficult to control. Wind causes a fire to burn more intensely, and increases the spread of fire by carrying hot embers to new fuel sources. Fuels with a low Fuel Moisture will burn very hot.
Weather data (temperature, relative humidity, wind direction, wind speed, and rainfall in the last 24 hours) from National Weather Service stations and local forestry offices is analyzed every morning. This analysis results in a predicted fire danger class day, which is broadcast statewide at 10 am daily. When conditions are critical by 2 pm, the day's weather data has been analyzed and an actual fire danger class day is broadcast statewide if necessary.
Following below is the official NWS fire Weather discussion as feed as required by the local Pittsburgh National Weather Service in Moon Township, PA (just outside of the city limits of Pittsburgh, PA.).
|Weather Definitions and Weather Facts|
The state of equilibrium in which a parcel of air when displaced has a tendency to move further away from its original position. It is the condition of the atmosphere when spontaneous convection and severe weather can occur. Air parcels, when displaced vertically, will accelerate upward, often forming cumulus clouds and possibly thunderstorms. Related terms: absolute instability, unstable and stability.