WindNinja is a simple diagnostic model designed for simulating microscale, terrain-influenced winds. A recent addition to WindNinja is a diurnal slope flow model. The model uses sensible surface heat flux, distance to ridge top or valley bottom, slope steepness, and surface and entrainment drag parameters to compute a diurnal slope wind. The diurnal wind can be combined with the ambient gradient winds. Testing of the model on a simple, hypothetical hill shows reasonable qualitative results. Fire spread simulations using FARSITE and the diurnal model show that the diurnal winds have some effect on predicted fire spread. The addition of the diurnal model is expected to be a simple, useful tool for fire analysts.