Forest fire managers must be able to predict the normal variation in fine fuel moisture around the clock, since it is a critical factor that affects the behaviour and control of wildfires and prescribed burns. The Canadian Forest Fire Weather Index System contains a Fine Fuel Moisture Code (FFMC) that produces a standard daily index of expected fine fuel moisture at the mid-afternoon peak of fire danger, but does not output normal diurnal variation in FFMC. This paper documents the development and updating of an earlier model of diurnal variation in FFMC, presents the underlying equations and a lookup table, and announces the availability of a computer program version of the model for various user applications.

Describes a model for predicting moisture content of fine fuels for use with the BEHAVE fire behavior and fuel modeling system. The model is intended to meet the need for more accurate predictions of fine fuel moisture, particularly in northern conifer stands and on days following rain. The model is based on the Canadian Fine Fuel Moisture Code (FFMC), modified to account for solar heating of fuels and to predict diurnal trends in fine fuel moisture. The model may be initiated without extensive data on prior weather. When compared to the FFMC and the fire behavior officers' procedures, the new model gave consistently better predictions over the complete range of fuel conditions.