What proportion of the rated capacity of wind power should be assumed available when performing a security analysis? This report answers the question by providing the regional and GB-wide probability distributions of wind power over three time periods: longterm, winter and during peak demand. To obtain these distributions, a methodology is provided. The methodology takes a dataset of hourly wind speed observations from the Met Office, cleans the dataset and models the wind speed as power output. The GB distribution is calculated from a weighted average of the regional distributions. The weights realistically reflect where current and future wind generation is and will be. It was found that the peak demand capacity factor is better than the longterm, but worse than the winter capacity factors.