Courtesy of Flowingdata.com, the WeatherSpark site is a graphic and historical representation of weather conditions.
From the site:
WeatherSpark is a new type of weather website, with interactive weather graphs that allow you to pan and zoom through the entire history of any weather station on earth.
Get multiple forecasts for the current location, overlaid on records and averages to put it all in context.
Unlike some mashups it is fairly apparent what is being used as a binding point. Which would make re-use of this data easier.
For example, if I were looking for weak points in a transportation system, I would take the traffic accident/delay records and then map them against the weather records from this site.
Thereby enabling predictions of when and where disruptive activity would have the greatest multiplier effect from natural weather conditions, time of day, etc.