The CPC weekly Degree Day Assessment discusses the Heating Degree Day (HDD) or Cooling Degree Day (CDD) outlook for the coming week, and reviews temperature and degree day statistics for the past week and the heating season (November - March) or cooling season (May - September) to date. This Assessment can assist energy managers in anticipating and analyzing fuel demand, because degree days quantitatively reflect the public need for energy to heat and cool businesses and dwellings.

For any individual day, degree days indicate how far that day's average temperature departed from 65 degrees F. HDD's, which measure heating energy demand, indicate how far the average temperature fell below 65 degrees F (since cooler weather means more heating fuel demand). Similarly, which measure cooling energy demand, indicate how far the temperature averaged above 65 degrees F. In both cases, smaller values represent less fuel demand, but values below 0 are set equal to 0, because energy demand cannot be negative. Furthermore, since energy demand is cumulative, degree day totals for periods exceeding 1 day are simply the sum of each individual day's degree day total. For example, if some location had a mean temperature of 60 degrees F on day 1 and 80 degrees F on day 2, there would be 5 HDD's for day 1 (65 minus 60) and 0 for day 2 (65 minus 80, set to 0 since degree days cannot be negative). For the day 1 + day 2 period, the HDD total would be 5 + 0 = 5. In contrast, there would be 0 CDD's for day 1 (60 minus 65, reset to 0), 15 CDD's for day 2 (80 minus 65), resulting in a 2-day CDD total of 0 + 15 = 15.

In this Assessment, degree day and temperature statistics are based on areally-averaged numbers for each of 102 climate regions of approximately equal area that cover the contiguous 48 states.

[NOTE:  HDD forecast statistics are not available for some areas because of data problems. These are indicated by gray shading on the maps showing U. S. Climate Region statistics. We are investigating this problem and hope to have it resolved soon. The Climate Prediction Center apologizes for any inconvenience this might cause.]

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