This Winter Is 37% Warmer than 2010-11 (by Heating Degree Days)

We celebrated Groundhog Day earlier this month. Naturally, that means we held our annual juggling festival here in Atlanta, but some people associate groundhogs with their weather forecasting ability. My question this year was, How can Punxatawney Phil (the weather predicting groundhog) or General Beauregard (his Southern counterpart) say anything at all about more winter when we haven't really had a winter at all? Yes, it's been quite warm this winter, especially in comparison to last year. So I thought I'd check to see just how much warmer it's been.

First of all, looking at the number of Heating Degree Days (HDD) is a great way to compare the cold weather of one year to another. There are three nice websites where you can get the Heating Degree Days for your location:

You should definitely check them out.

Heating Degree Days are a way of looking at how much time your area has spent below a given temperature, called the baseline temperature. The most commonly used baseline here in the States is 65° F, so here's how what it means:

1 minute at 64° F gets you 1 Heating Degree Minute.
1 hour at 60° F would be 5 Heating Degree Hours.
24 hours at 30° F accumulates 35 Heating Degree Days.

See how it works?

One way that you can use these numbers is to calculate the amount of heating your home needs. Since your heating load depends on how cold it is outside, the more Heating Degree Days you have, the more heating you have to pay for. The basic equation for this is:

The number of Heating Degree Days tells you the ΔT over a given time period.

So, here in Atlanta, we had a total of 3396 HDD in the 2010-11 winter. It was really cold last year, and we actually had snow three times. We normally get one little snow a year, but we even got shut down for a whole week with snow that turned to ice on the roads and then stuck around. Our 30 year average is about 3000 HDD, so last year was colder than normal.

This year however, if we look just at December and January, we find a huge difference:

December 2010: 891
December 2011:506

January 2011: 823
January 2012: 570

The 37% number in the title of this article comes from comparing the HDD of just those two months. We had 1714 HDD in those months in 2010-11 and 1076 HDD this winter. It's great for heating bills and getting outside and doing stuff here. Not so great killing bugs though.

How do your Heating Degree Days this winter compare to last winter?

This article was one of many that we publish in the Energy Vanguard Blog. To get them all as they're published, you can subscribe to our blog by entering your email address in the box at the top of the page.

Photo by AlicePopkorn2 from flickr.com, used under a Creative Commons license.

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Comment by David Meiland on February 21, 2012 at 8:02am: My perception was that we have had a warm winter, but comparing December and January this season to last, it has actually been a bit colder this season.

Comment by Edythe Moore on February 20, 2012 at 4:58pm: We are in Michigan, "the Winter Wonderland!" and my friends in Dallas Texas got more snow then Michigan this year. I can't recall a November in Michigan where I only wore a sweater for outerwear!

Comment by Paul Raymer on February 20, 2012 at 7:42am: From the log on my office, we are about 30% warmer this Dec + Jan than last year. The way it's going this February, looks like it will be equally as warm. The only measurable snow we have had here on Cape Cod was while I was away at the ASHRAE conference and my wife was left to shovel the driveway! Our 2009 HDD were 5211, 2010 = 5403, 2011 = 4955. I heard there is an organization for non-skiers that has been started - "Central New Yorkers for Global Warming!"

Comment by Craig A. Lawson on February 20, 2012 at 7:11am

There's 12 months. Here's the data taken from the KSTS station

Station:	SANTA ROSA SONOMA COUNTY, CA, US (122.81W,38.51N)
Station ID:	KSTS

Month starting	HDD
2/1/2009	489
3/1/2009	438
4/1/2009	357
5/1/2009	250
6/1/2009	186
7/1/2009	211
8/1/2009	179
9/1/2009	176
10/1/2009	271
11/1/2009	462
12/1/2009	652
1/1/2010	549
	4220

2/1/2010	430
3/1/2010	470
4/1/2010	416
5/1/2010	313
6/1/2010	158
7/1/2010	191
8/1/2010	208
9/1/2010	170
10/1/2010	252
11/1/2010	429
12/1/2010	481
1/1/2011	580
	4098

2/1/2011	510
3/1/2011	431

Comment by Ed Minch on February 20, 2012 at 6:59am: Craig

Is there a reason you only accounted for 11 months of each year? That would make the 12 month totals even worse when adding January to each.

Comment by Craig A. Lawson on February 20, 2012 at 6:52am: Santa Rosa, California

2/1/09 to 1/1/10 = 4,220 HDD

2/1/10 to 1/1/11 = 4,098 HDD

2/1/11 to 1/1/12 = 4,183 HDD

100 year average = 3,019 HDD

In our local, it begs the question, "Where's the heat?"

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