This Demonstration plots cumulative cooling and heating degree days with cooling days as negative values to show undulating seasonal weather patterns. Each plot has two major features. The undulation of the seasons, with more heating days around summer and more cooling days around winter shows an annual cycle. Also there is an overall drift, downward for the cooler cities in the north and upward for the relatively warmer cities. This is simply a result of the net excess of heating or cooling degree days in the annual cycles of warm or cool locations.
These main features plus nonstationarity from the randomness of weather and longer-term changes are important aspects of understanding and forecasting the climate. This Demonstration applies to the eighteen cities covered by the exchange traded weather futures (at the Chicago Mercantile Exchange).