|
|
A Value-Added Approach in Calculating Daily Degree Days
| Click on the calendar to view past maps: |
|
| Data is available since January 21, 2012 |
Background:
The NWS method of determining heating and cooling degree days is based off a mean temperature of the day by taking the average
of the daily maximum and minimum temperatures, or (Tmax + Tmin)/2. Other statistical methods have been shown to be more
accurate, utilizing either hourly degree days or the average temperature of the day. As a demonstration of the potential
value of using such methods, the plots below compare differences in daily degree days between the current NWS method and
a scheme using the average temperature of the day, Tavg (where Tavg = (T1 +T2....+T24)/24). While differences on any given day
are relatively small, prior research has shown that correctly forecasting these differences may contribute to substantial
revenue savings to regional utility companies over longer time scales. The maps below show observed degree days using the
current NWS method (Tnws), calculated degree days using the daily averaging scheme (Tavg), and resultant differences between
each (Tdif). For a full description, see here |
Click to enlarge 
NWS Method (Tnws) |
Click to enlarge 
Daily Averaging Method (Tavg) |
Click to enlarge 
Difference (Tdif) |
Disclaimer:
Maps shown are 2.5km resolution and incorporate 24 hour observational data from quality controlled data sources.
Slight differences of up to 1 degree day may be noted between the Tdif plots and the actual difference values represented
in the two methods. Differences are due to several contributing factors, including numerical rounding and
background mapping techniques. These factors also contribute to the apparent "herringbone" pattern in the Tdif maps. Heating
(Cooling) degree days are depicted as negative (positive) values in Tnws and Tavg maps. Tdif values are always positive, as
they express the absolute value in the difference between Tnws and Tavg. |
|
|
weather.gov 
