Fine fuel moisture (FFM) measures the percentage of water weight in dead plant material less than one quarter inch in diameter, such as grass, pine needles, and small twigs. These fuels dry out quickly and respond rapidly to changes in humidity and temperature. Wildland firefighters monitor this metric because low moisture levels mean a fire will ignite easily and spread rapidly.
The FFM dropped below five percent this afternoon, so expect extreme fire behavior if a spark lands.
Related terms
Flash fuel
Lightweight, highly combustible vegetation that ignites easily and burns rapidly.
One-hour fuel
Dead vegetation less than a quarter-inch in diameter that reacts rapidly to changes in relative humidity.
Firebreak
A gap in vegetation or other combustible material that acts as a barrier to slow or stop the progress of a wildfire.