Midflame Wind Speed

The speed of the wind measured at the midpoint of the flames, considered to be most representative of the speed of the wind that is affecting fire behavior. Fire behavior models calculate midflame windspeed from 20 foot winds using a wind reduction factor. In IFTDSS, Landscape Fire Behavior and Landscape Burn Probability it is the wind velocity at the midflame height.

In IFTDSS this is expressed in miles per hour in the Map Studio and download outputs.

The calculations use midflame wind speed, which is derived from the 20 foot wind speed entered. For each cell in the landscape, a wind adjustment factor, based on canopy height and canopy cover, is applied to convert the 20 foot wind speed to a midflame wind speed. Note that wind direction for each cell is modeled over space, the wind is not changing over time.

The image below demonstrates typical fuel sheltering for slope locations. The midflame windspeed will be LESS THAN the 20-foot windspeed, because vegetation and friction slow down winds closer to the surface. That is why all the adjustment factors in the table are less than 1.

Partially sheltered fuels are associated with Midflame wind speeds of about 1/3 that of 20 foot wind speeds. Fully sheltered fuels are associated with Midflame wind speeds of about 1/5 that of 20 foot wind speeds. Unsheltered fuels have midflame windspeeds of about half that of 20 foot wind speeds.

For a detailed explanation of Midflame Wind Speed concepts we recommend reading the NWCG web page on Midflame wind speed .

Midflame windspeed can be viewed in Map Studio