Spring begins next Monday (1 March 1999) - at least in terms of the meteorological seasons. For many areas of the country, spring-like conditions have prevailed for the last month. However, the deep snow found along the Sierras and the Cascades makes spring seem distant. So before we can close the books on the three month winter season (December, January and February) we should take a look to see its severity.
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, how has the winter of 1998-1999 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. 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. The recently compiled data for the month of January, 1999 serves as an example. The number of heating degree days 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 1961-1990 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.
By the end of January, many sections of the country typically have experienced the coldest conditions from a climatological viewpoint and the heating season has reached the half way point. Inspecting the state-wide heating degree data through January reveals that with the exception of California, all the states have accumulated fewer heating degree days units so far during this 1998-1999 heating season as compared to the corresponding 30 year "normal" heating season. The eastern and western South Central states had the greatest percentage-wise departure, or approximately 20 percent less than the long term average. The New England States had the smallest relative departure, with approximately 5 percent fewer heating degree day units as compared with the average. Suprisingly, much of the country with the exception of the Pacific States (California, Nevada, Oregon, Utah and Washington), also accumulated fewer heating degree day units than the previous heating season, which had relatively few heating degree day units, courtesy of the El Niño episode that contributed to the warmest winter season across the northern tier of states since 1895.
Ultimately, the "bottom line" has been that for most residents across the country, to date, the mild winter weather would demand less energy as compared to the long term average, and therefore not strain the pocketbook - assuming that monetary inflation or other non-weather related price increases are not taken into account.
Corresponding sets of cooling degree day units for selected cities and for population weighted regions were also compiled. Since the cooling season only started on 1 January and most locales have not experienced daily average temperatures above 65 degrees, analysis of these statistics is somewhat premature. Florida and Hawaii accumulated greater than average cooling degree days units during January, while the other states across the Sun Belt, stretching from California east to the Carolinas had slightly below averag cooling degree day units.
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Prepared by Edward J. Hopkins, Ph.D., email hopkins@meteor.wisc.edu
© Copyright, 1999, The American Meteorological Society.