Pat,
I have never looked at degree days in WD, but it looks as though its using the simple formula.
degree day base value +/- mean temp.
So if the mean temp is 70 your cooling degree day value would be 5 (assuming 65 base value)
if your mean temp was 60 your heating degree day value would be 5.
If you mean temp has not gone above 65 for day / month / year you will have a cooling degree day value of zero.
I know VWS uses this simple method.
On your weatherlink noaa summary it show cooling degree days, it also says Method: integration. For this method the software calculates degree–days using the average temperature for an interval and the interval time. So its possible to have both, as you indicated by the 5.1 cooling degree day you noticed yesterday.
The integration method appears to be better to show actual heating or cooling needs, but hard to replicate by yourself. Obviously if your daily average temp is 64, you would not have any cooling degree days shown using simple method. but in that day if it was 90 degrees for 3 hours, chances are your air co will have kicked in......and the integration method would have captured that in its calculation.
Andrew
