WindNinja is a computer program that computes spatially varying wind fields for wildland fire application. It requires elevation data for the modeling area (in the form of an ASCII Raster DEM file), a domain-mean initial wind speed and direction, and specification of the dominant vegetation in the area. Outputs of the model are ASCII Raster grids of wind speed and direction (for use in spatial fire behavior models such as FARSITE and FlamMap), a GIS shapefile (for plotting wind vectors in GIS programs), and .kmz files (for viewing in Google Earth). WindNinja is typically run on domain sizes up to 50 kilometers by 50 kilometers and at resolutions of around 100 meters. It is currently in development, but a beta version is available.

WindNinja runs much faster than WindWizard, with typical run times of a few seconds to 5 minutes depending on hardware and program settings. These short run times are possible because of incorporation of less physics than WindWizard (specifically the handling of momentum). This can lead to less accurate results predominantly in the lee areas of hills/mountains where recirculation zones would be expected to occur.

Both WindNinja and WindWizard must make certain physical approximations to make development and its use by fire managers possible. An important assumption the user should be aware of is that of a neutrally stable atmosphere. This means that the models do not include buoyancy effects due to diurnal flows, non-neutral stability, or the fire itself. The wind models should therefore be most accurate when these effects are small compared to the ambient wind.