weathersupermarket.co.uk is a broker for weather forecasts. This works on same principle as the increasing popular price comparison sites, "compare the market", "money-supermarket" etc.
There are many forecast providers whose forecasts can vary widely. Users can view a summary of forecasts to quickly see the best and worst with a star rating.
Users enter a location of interest, weathersupermarket then checks with each forecaster whether they can forecast for that location, and asks the user to resolve any ambiguity in the location entered.
weathersupermarket provides all the forecasts in a table with a column for each day.
Source data is a mixture of RSS and screen scrapes. All data is then standardized to allow unified display.
All forecast providers use different systems for mapping search strings to forecast locations. To overcome this visitors are presented with drop-down lists to confirm ambiguous locations, e.g. Manchester in UK or US. The choosen IDs are then passed onto the next stage of the process that requests the forecast.
Each forecast also has a star rating. The algorithm for this uses simple fuzzy logic scoring based on temperature and keywords. Keywords are scored and averaged, e.g. rain is negative 1, heavy rain negative 2, sunshine positive 2 etc.