EFFECTS OF VARIOUS PARAMETERS 

Wind:  Winds usually result in more rapid combustion due to more oxygen being available for the combustion process. Wind will also lean flames closer to the fuel resulting in more preheating. Fires burn more intense and faster.  Helps to disperse smoke.

Temperature:  Higher temperatures result in more kill.  Convected heat can result in excess crown scorch.  Remember that the heat produced by the fire will be added to the heat (ambient temperature) that is already there.

Relative Humidity:  Low humidity results in a faster, cleaner burn but usually associated with unstable conditions.  High humidity results in a slower burn with more smoldering smoke. 

Stability:  Unstable conditions result in rapid, intense burning that can be very intense if moderate to heavy fuel loading.  Conditions can also change rapidly.  Smoke is lifted off the ground but control could be a problem. Slightly unstable to unstable conditions are best for prescribed burning. More unstable conditions result in a more intense fire that more readily lifts the smoke and moves it on out of the area. However, such fires may cause damage to an overstory that is low. Control also may be a problem.

Fuel Moisture:  High fuel moisture will result in a smaller percent of the fuel being available.  Fire intensity and spread will be slower with larger than average amounts of smoke being produced because more heat will be used in driving out the moisture in the available fuel.

Fuel Loading: If fuel loading is high but a low intensity fire is desired, wait until after a period of rains when fuel is thoroughly soaked, then burn after a few days of dry weather when the top of the litter and the fine fuels are dried out and will burn but most of the fuel will still be too wet to burn.

The lower the moisture in the fuel that burns, the less smoke will be produced. 

Fine Fuels:  Fine fuels that are loosely arranged will burn rapidly with most, if not all of the fuel being consumed during the flaming phase producing much less smoke. They also help to dry out larger fuel.

Slope: Prescribed fires are used more predominantly in the coastal and lower piedmont areas where slopes are moderate or don’t exist. They have little effect on fire behavior during the day. At night however, the wind generally dies down and there is little or no heat to lift the residual smoke that may be produced. It will tend to stay close to the ground and flow down-slope and down-drainage. It will flow down even the slightest slope and concentrate in low areas. This has become a major problem when prescribed burning, especially when large amounts of residual smoke are produced.

Time of Day: All elements of weather tend to change during the 24- hour day. As a result, fires will be the most intense during the middle of the day and early afternoon. Spread will also be the most rapid. Due to the lag-time for fuels to lose moisture, they will be the driest during the middle to the late part of the afternoon.