# make an arc to Arcturus, and speak to Spica

By: superfalke , 6:17 AM GMT on February 21, 2010

Beautiful winter sky around midnight, with the moon low in the sky.

Using "Yesterday's Official Weather and Almanac", and looking at the data below, i have to wonder:
What sort of math takes (-5), adds (2), and averages the result to arrive at (0)? That is, to get 26 heating degree days for both Actual and Average.

Roanoke data for 2/19/10:

...........Actual.....Avg.....Record
Max Temp.....45.....50.....77 (1939)
Min Temp.....32.....30......7 (1979)

Heating Degree Days:
.............26.....26

Since 7/1/09 heating degree days:
...........3112.....3086 (how about that, 26 hdd above normal)

Here's the explanation.
When rounding off, if you're exactly in the middle, then round off to the even number. Also, in this case, compute the contributions from MIN and MAX temps separately. For example, the actual MIN was 32, so its contribution to total heating degree days = (65 - 32)/2 = 16.5 which rounds down to 16.

Actual MIN (20/2) = 10
Actual MAX (33/2) = 16.5 ==> 16
HDD = 10 + 16 = 26

Average MIN (15/2) = 7.5 ==> 8
Average MAX (35/2) = 17.5 ==> 18
HDD = 8 + 18 = 26

=====================================================

Looks like we've got a horse race this year anyway. Could be the first time in a long time to have a colder than normal heating season. Need to break 4284 hdd to make it happen here in Roanoke VA.

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##### 1. unclemush
7:02 AM GMT on February 21, 2010
 Nice pictures! :)
Member Since: July 7, 2001 Posts: 60 Comments: 13187

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### superfalke's WunderBlog

Superfalke was a Scheibe motorglider that flew from San Diego to New Castle VA in 1983.

### Local Weather

 Roanoke, Virginia 76 °F Overcast

### Personal Weather Stations

 Coopers Cove at Lakeshore Terrace Hardy, VA Elevation: 912 ft Temperature: 75.8 °F Dew Point: 70.3 °F Humidity: 83% Wind: Calm Wind Gust: 8.0 mph Updated: 8:59 AM EDT on July 29, 2016 Station History