The McArthur forest and grassland fire danger meters estimate fire behaviour from measurements of wind speed, fuel moisture content and drought for specific fuel types. They also combine the most important fire danger variables to estimate rate of fire spread and flame height. They work best during long, dry periods, when grasses are fully cured and when forest fuels do not contain residual moisture from recent rain and the maximum amount of fuel is available for combustion.
Local variation of wind speed will occur, particularly in mountain topography, and fire fighters must take care to observe the wind speed in a clear, open site. They must not be lulled into a false sense of security by the presence of relatively light winds on sheltered aspects or in the lee of the convection column of a large fire.
RATES OF SPREAD, FLAME HEIGHTS AND BEHAVIOUR PREDICTIONS ARE ALL MINIMUM AND SEVERE BEHAVIOUR WELL ABOVE THE METER'S PREDICTIONS MAY BE EXPECTED AT FIRE DANGER RATINGS OF HIGH, VERY HIGH OR EXTREME.
These programs are based on a paper by Noble, Bary and Gill "McArthur's fire-danger meters expressed as equations" 1980.