The weather has an effect on energy supply and demand. For instance, if there is a major heatwave in Western Europe, power companies will need to increase their output for cooling purposes. So what these companies need is someone who can predict these anomalies in the weather and thus become hedged against adverse price movements in the natural gas and crude markets. There also is actually a contract traded on the CME called a weather derivative used as insurance against adverse temperatures.
The weather also affects agricultural commodities such as soybeans and wheat, et cetera. Major shifts in weather forecasts cause changes in market prices because weather affects planting, output and supply concerns during the growing seasons.