A familiar gauge used to assess a winter's severity is the amount of heating fuel that we need to use to keep our homes warm over the winter. In other words, during the next several months many of us will inquire as to how the winter of 2007-2008 has affected our pocket books when it comes to space heating. For comparison purposes, we may try to remember how this winter compares with last winter or to some long-term average. We can monitor this situation by regularly returning to the tabulations of heating degree-day units.
The heating degree-day unit has been a useful indicator that gauges the amount of energy required for space heating. During the first several days of each new month, the Climate Analysis Center of the National Weather Service compiles heating degree data for the previous month and posts these data for selected cities around the country. Since the statistics for September are yet to be processed, those statistics for August will serve as an example. The number of heating degree-day units accumulated for the month appears in the column marked "Monthly Total". Adjoining columns display the comparisons between this year and the "normals", as well as with last year. Specifically, the arithmetic differences between the month totals from this year and the "normals" representing the 30-year averages for the current 1971-2000 climatological reference interval appear in the column marked "Month. Dev. from Norm." The difference between this year and the same month last year appear in the column "Month. Dev. from L. YR." Similar columns show the comparisons between the total number of heating degree day units accumulated over the current heating season that started on 1 July and the corresponding values for normals to date and last season to date. Percentage differences are also presented.
The climatologists at the Climate Analysis Center have also prepared a corresponding list of population weighted heating degree-day units for each state. These latter statistics are used to show the temperature-related energy consumption on the state, regional, and national levels.
Since the heating season was only 2 months old for the provided table and most locales have not experienced daily average temperatures significantly below 65 degrees Fahrenheit, analysis of these statistics is somewhat premature. A more meaningful analysis could be made by revisiting this site in several months as winter begins in earnest across many portions of the country. The preliminary results through August indicate that nationally, fewer heating degree-day units had been accumulated for the season (since July) than the 30 year "normal". New England and the Middle Atlantic States had slightly higher accumulated totals than average. In addition, this region plus the North Central States had slightly more heating degree-day units were accumulated as compared with the first two months of the previous 2006-2007 heating season. Unseasonably warm weather across the Rocky Mountain and Pacific States during this summer has meant fewer heating degree day units as compared with last season.
Corresponding sets of cooling degree-day units for selected cities and for population weighted regions were also compiled. These statistics indicate that the entire country experienced a greater number of cooling degree-day units for the first eight months of the year than the 30-year climatological "normals" to date, which represents a 10 percent increase over "normal". This result should not be surprising, since scientists at the National Climatic Data Center recently reported that the summer of 2007 (June through August) was the sixth warmest summer nationwide since records began in 1895. Furthermore, all regions except for the West South Central States reported above normal cooling degree-day units. When compared with the 2006 cooling season, most sections of the nation experiencing fewer cooling degree days in the 2007 season to date, with the nationwide average for this cooling season to date experiencing a 5 percent decrease from the 2006 season. Scientists last year reported that the first eight months of 2006 had been the warmest on record across the nation. This year, only the East North Central, East South Central and Mountain States had slightly more cooling degree days than last year to date. How these cooling degree statistics translate into a change in the cost of your utility bill is not as clear-cut as the cost relationship with the cumulative heating degree-day units. Other factors, such as the atmospheric humidity levels, the amount of sunshine and your life style may also significantly influence your decision to run your air conditioner.