The annual mean wind speed value we provide is our best estimate of the actual mean value. The +/- (plus or minus) symbol indicates that the true annual mean value is within a range plus or minus the number shown after the provided wind speed value. The Prospecting Tools directly incorporate a confidence interval for the annual mean wind speed data, showing a range of expected wind speed values, to provide a realistic assessment. We are 68% confident that the true annual mean wind speed for a given location falls inside the displayed range. The narrower the range of wind speeds, (i.e. the smaller the +/- value we show) the more confidant we are concerning the long-term annual mean wind speed value.

For any location, the annual mean range is only meant to be used at the prospecting stage and doesn’t present the full story of a potential site. Data on annual and diurnal variability, prevailing wind direction, and many other atmospheric factors are necessary to more accurately assess the wind resource at any given location.