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, FARSITE landscape file, GeoTiff, or ERDAS Imagine file), a domain-mean initial wind speed and direction, and specification of the dominant vegetation in the area. A diurnal slope flow model can be optionally turned on or off. 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 a .kmz file (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.