The US Department of Energy's Wind Program and the National Renewable Energy Laboratory (NREL) published a wind resource map for the state of Montana in 2010. The map shows the predicted mean annual wind speeds at 80-meter height. The data are presented at a spatial resolution of about 2 km (interpolated to a finer scale for display). The data are estimates by AWS Truepower. This map is better used to identify high potential areas for wind prospecting than for actually siting turbines.
NREL map of estimated wind speed at 80 m
DEQ produced similar maps from a 2002 NREL data set that show estimated wind speed at 50 meters. These maps show the transmission grid and highlight either state-owned or Bureau of Land Management (BLM) lands.
DEQ map of estimated wind speed at 50 m highlighting State-owned lands
DEQ map of estimated wind speed at 50 m highlighting lands owned by BLM
The 2002 wind resource estimates used by DEQ were developed using MesoMap, a wind mapping system developed by TrueWind Solutions. MesoMap combines two models, MASS, a mesoscale atmospheric simulation model similar to a weather forecasting model, and WindMap, a simples wind flow model. The results were validated by NREL and independent meteorologists using historical data. Wind speeds shown are estimated to be within about +/-5% accuracy, and wind power density values (which are related to the cube of the speed) are estimated to be within about +/-15% accuracy. This means that the actual wind speed should be within 5 percent of the predicted at two-thirds of the locations on the map, and should be within 10 prcent of the actual at about 95 percent of the locations, assuming that the measurements are taken in well exposed areas, with minimal obstructions, and following wind industry measurement guidelines.
The two models work together, but at different scales. MASS operates on a spatial grid resolution of 2.6 km (1.6 miles), whereas WindMap operates on a resolution of 400 meters (1312 ft, or one-quarter mile), which is the final scale of the maps. While WindMap can simulate the acceleration of winds over small hills and ridges, many other terrain effects require the more sophisticated MASS. Such effects include channeling through valleys or passes (such as Judith Gap or Livingston Pass) and downslope flows (e.g., Blackfeet area). To the extent these effects are at work, the accuracy of the maps is limited by the spatial grid resolution of MASS. To be resolved completely, a terrain feature must be larger than about 3-4 grid cells. Therefore, for instance, a valley that is less than about 7-10 km wide will not be fully "seen" by the MASS model, and if there is any channeling through that gap, it will be underestimated or entirely missed in the map. Likewise, detailed aspects of a downslope flow, including its intensity and full extent, will not be resolved better than the scale of the MASS simulations.