From: Subject: Wednesday Weather Topic in Greater Depth Date: Thu, 8 Oct 2009 10:02:19 -0700 MIME-Version: 1.0 Content-Type: text/html; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable Content-Location: http://www.ametsoc.org/amsedu/online/archive/course/09_fall/f09w04w_sup.html X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5579 Wednesday Weather Topic in Greater Depth

SUPPLEMENTAL INFORMATION...IN GREATER DEPTH

To complement the Daily Summary for Wednesday, 30 = September=20 2009

MONITORING DEGREE DAY UNITS

A familiar gauge used to assess a winter's severity is the amount of = heating=20 fuel that we need to use to keep our homes warm over the winter. In = other words,=20 during the next several months many of us will inquire as to how the = winter of=20 2009-2010 has affected our pocket books when it comes to space heating. = For=20 comparison purposes, we may try to remember how this winter compares = with last=20 winter or to some long-term average. We can monitor this situation by = regularly=20 returning to the tabulations of heating degree-day units.

The heating degree-day unit has been a useful indicator that gauges = the=20 amount of energy required for space heating. During the first several = days of=20 each new month, the Climate Analysis Center of the National Weather = Service=20 compiles heating degree data for the previous month and posts these data = for selected=20 cities around the country. Since the statistics for September are = yet to be=20 processed, those statistics for August will serve as an example. The = number of=20 heating degree-day units accumulated for the month appears in the column = marked=20 "Monthly Total". Adjoining columns display the comparisons between this = year and=20 the "normals", as well as with last year. Specifically, the arithmetic=20 differences between the month totals from this year and the "normals"=20 representing the 30-year averages for the current 1971-2000 = climatological=20 reference interval appear in the column marked "Month. Dev. from Norm." = The=20 difference between this year and the same month last year appear in the = column=20 "Month. Dev. from L. YR." Similar columns show the comparisons between = the total=20 number of heating degree day units accumulated over the current heating = season=20 that started on 1 July and the corresponding values for normals-to-date = and last=20 season-to-date. Percentage differences are also presented.

The climatologists at the Climate Analysis Center have also prepared = a=20 corresponding list of population-weighted=20 heating degree-day units for each state. These latter statistics are = used to=20 show the temperature-related energy consumption on the state, regional, = and=20 national levels.

Since the heating season was only 2 months old for the provided table = and=20 most locales have not experienced daily average temperatures = significantly below=20 65 degrees Fahrenheit, analysis of these statistics is somewhat = premature. A=20 more meaningful analysis could be made by revisiting this site in = several months=20 as winter begins in earnest across many portions of the country. The = preliminary=20 results through August indicate that nationally, slightly more heating=20 degree-day units had been accumulated for the season (since 1 July) than = the=20 30-year "normal". The New England and the eastern South Central States, = along=20 with the North Central States (eastern and western) had higher = accumulated=20 totals than average in July and August 2009. Elsewhere, fewer heating = degree-day=20 units were accumulated. In addition, most of the regions of the = continental=20 United States had more heating degree-day units that have been = accumulated this=20 summer as compared with the first two months of the previous 200 8-2009 = heating=20 season.

Corresponding sets of cooling degree-day units for selected=20 cities and for population-weighted=20 regions were also compiled. These statistics indicate that despite a = cool=20 summer across the Northeast and the Midwest, the entire country = experienced more=20 cooling degree-day units for the first eight months of the year than the = 30-year=20 climatological "normals" to date. This higher number represents a = two-percent=20 increase over "normal". Interestingly, scientists at the National = Climatic Data=20 Center recently reported that the summer of 2009 (June through August) = was the=20 33rd coldest summer nationwide since records began in 1895, with many of = the=20 states across the nation's midsection experiencing below to much below = normal=20 summer temperatures, while the West Coast and Gulf Coast States had = above normal=20 statewide temperatures. Not surprisingly, the East and West Central = States had=20 between 24 and 26-percent fewer cooling degree-day units, reflective of = below=20 average summer temperatures, while the Pacific Coast States had a = 24-percent=20 greater number of cooling degree days, corresponding to the persistent = heat=20 experienced there. When compared with the 2008 cooling season, most = sections of=20 the nation experiencing fewer cooling degree days in the 2009 season to = date,=20 with the nationwide average for this cooling season to date experiencing = a=20 three-percent decrease from the 2008 season.

How these cooling degree statistics translate into a change in the = cost of=20 your utility bill is not as clear-cut as the cost relationship with the=20 cumulative heating degree-day units. Other factors, such as the = atmospheric=20 humidity levels, the amount of sunshine and your life style may also=20 significantly influence your decision to run your air conditioner.

Return to the Wednesday=20 Daily Weather Summary

Prepared by Edward J. Hopkins, Ph.D., email hopkins@meteor.wisc.edu =
=A9=20 Copyright, 2009, The American Meteorological Society. =