Most of us are familiar with the adjective terms low, moderate, high, very high and extreme in regards to fire danger. Fire danger ratings are typically reflective of the general conditions over an extended area, often hundreds of thousands of acres. The National Weather Service provides forecast observations that are used to calculate the forecast fire danger rating.
In fact, weather parameters are used to determine fire danger. Temperature is the single most important weather factor affecting fire behavior. Warm fuels will ignite and burn faster because less heat energy is used to raise the fuels to their ignition temperature. Fuels exposed to sunlight will be warmer than the fuels in shade. They will also be drier.
Wind is another factor impacting fire danger. Wind influences the rate of spread and intensity of the fire. High winds will cause the head of a fire to move ahead rapidly. It may cause the fire to crown into the top of the trees and to jump barriers that would normally stop a fire. Wind can carry sparks and firebrands ahead of the main fire causing spotting. Wind also increases the supply of oxygen, which results in the fire burning more rapidly. It can change speed, direction, or become quite gusty which makes it harder to fight.
Relative Humidity also affects fire danger. Relative humidity is the term used in prescribed burning to express the amount of moisture in the atmosphere. The lower the relative humidity, the more readily a fire will start and burn, the more vigorously a fire will burn.
A prolonged period of dry conditions with little or no rain can also raise fire danger. In Southwest Florida's dry season, the lack of rainfall causes a peak fire season between the months of March and May. Since January 1st, Page Field in Fort Myers has had roughly 3 inches of rain, which is close to 3 inches below average. This has led to a moderate drought in Lee county and across all of southwest Florida.
The below average rainfall, combined with low relative humidity under 35% and warm temperatures have prompted the very high fire danger for Lee and Hendry counties and a high fire danger for the rest of Southwest Florida April 2nd. Humidity will be a bit higher Friday which has led to a moderate to high fire danger across all of Southwest Florida. Wind will be around 10 mph the next several days which helps as well. Unfortunately the first half of April looks to be below average in regards to rain which will not help our drought. However, rainy season is right around the corner which will help our drought conditions and fire danger for all of Southwest Florida.