The Met Office has developed the Virtual Met Mast ™ (VMM) tool for assessing the feasibility of potential wind farm sites. It provides site-specific climatological wind information for both onshore and offshore locations. The VMM relies on existing data from past forecasts from regional-scale numerical weather prediction (NWP) models, to which corrections are applied to account for local site complexity. The techniques include corrections to account for the enhanced roughness lengths used in NWP models to represent drag due to sub-grid orography and downscaling methods that predict local wind acceleration over small-scale terrain. The corrected NWP data are extended to cover long periods (decades) using a technique in which the data are related to alternative long-term datasets. For locations in the UK, the VMM currently relies on operational mesoscale model forecast data at 4 km horizontal resolution. Predictions have been verified against observations made at typical wind turbine hub heights at over 80 sites across the UK. In general, the predictions compare well with the observations. The techniques provide an efficient method for screening potential wind resource sites. Examples of how the VMM techniques can be used to produce local wind maps are also presented. 411 2. The long-term data at the reference location must be of a consistently high quality, with known instrument faults or changes corrected. The period must be sufficiently long to represent the local climatology. Typically, a minimum period of 20 years is required. The reference location should be close to the site of interest and sufficiently similar in nature that the wind at the two sites is strongly correlated. Clearly, if the winds experienced at the sites are very different (due to local topographic variations, for example), then the method will fail. Modelling techniques can be used to account for the effects of local site complexity, but the difficulties of modelling airflow in complex terrain mean this may not be successful. [8][9][10] An alternative approach to MCP is to generate synthetic reference climatology data. Over recent years, there has been a growing trend of the use of numerical weather prediction (NWP) data for the generation of climatological wind predictions. 4,11 Run at sufficiently high horizontal resolution, modern NWP models can, in principle at least, account for local variations in orography and the land surface and therefore be used to generate site-specific wind predictions. One advantage of using model data over reference observations is that model data can be co-located with the target site, avoiding the uncertainties due to using observations at a different site. A recent study 12 shows that using model data in place of reference site observations can work well in a MCP approach.The use of NWP data for climatological wind predictions relies on an accurate model run at high spatial resolution. The resolution requirements will generally depend on the site location. A relatively coarse horizontal grid spacing of a fe...