Abstract: Methods and articles of manufacture for providing an indication or representation that describes the state of weather over a period in the past for a particular location. Observation data for the location is accumulated and stored over the period. Because forecast engines exist and can be adapted for use in determining the indication of weather, the observation data is converted into a format of forecast data. The data is then grouped into subsets and processed as forecast data. For each subset, a representation of weather is determined. The representations of weather for each subset are then processed to determine the representation of weather for the period of time.