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.