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Posted at 10:00 AM ET, 01/24/2011

D.C. Decembers: Trending colder?

By Matt Rogers

Top 10 coldest Decembers in D.C. since 1950

We've had some mighty cold days this January (how about this morning's lows of 6 degrees at Dulles Airport and 17 at Reagan National?). But the current departure from average for the month of -1.1F pales in comparison to December's -4.9F. It turns out that December 2010 in Washington, D.C. (as observed at Reagan National), was the eighth coldest on record since 1950. The official top-10 ranking is shown to the right.

Some of you may remember the brutal December 1989 (No. 1 on the list) around here. What's especially fascinating is that every decade is represented on the top-ten list except for the warmer 1990s. The 1950s and 1960s scored the most with three each.

To put December 2010 into deeper historical context, I decided to look at things from a decadal perspective.

I calculated D.C.'s average December temperature for each decade (1950-1959, 1960-69, etc.) and found some interesting results. I think most would guesstimate an upward temperature trend. Not so for December in D.C.:

Average December temperature in D.C. by decade.

What really surprised me is that Decembers in the 1970s, especially the first half of the decade, were warmer in D.C. than the 1980s. More recently, the 2000s have come in colder than the 1990s, and here we are with a chilly start to the 2010s. If anyone asks you what the coldest decade is for D.C. Decembers, you can answer the 1960s (of course, pending how the 2010s play out).

Finally, I wanted to see if there was any definable trend for D.C. Decembers. So, I plotted the five-year running average of the D.C. December average temperature and found the following...

Five-year running average of D.C.'s average December temperature.

A warming trend definitely existed from the 1950s to the 1970s, but temperatures have been relatively level ever since. The most recent peak period in the 1990s has certainly relaxed somewhat. The 2010 December average of 34.6F is quite a ways below the five-year running average. Why is our five-year average so warm given the cold December 2010? Because we had three relatively warm Decembers in a row that were at or above 40F for the average temperature (2006, 2007, 2008).

What's responsible for the recent cold? A big reason appears to be that oceanic oscillations, such as the North Atlantic Oscillation, in the Atlantic and Pacific are shifting into phases that generally lead to colder winters for the eastern half of North America.

I'll look at January next month.

(Note: if we look at a longer time period, dating back to 1880, December 2010 was the 30th coldest on record, as Ian mentioned a couple weeks ago. However, D.C.'s observing site was in different locations prior to the early 1940s when it moved to National Airport)

Data Source: Speedwell Weather and NOAA.

By Matt Rogers  | January 24, 2011; 10:00 AM ET
Categories:  Latest, Local Climate  
Save & Share:  Send E-mail   Facebook   Twitter   Digg   Yahoo Buzz   StumbleUpon   Technorati   Google Buzz   Previous: Forecast: Cold, but warming before Wed. storm
Next: Near rain-snow line for significant Wed. storm


Folks- a reminder that we'll have an updated post on the Wednesday storm in a little while. Aiming for before noon. Suggesting discussing Wednesday storm in my earlier forecast post thread and keep discussion here focused on temperatures.

Posted by: Jason-CapitalWeatherGang | January 24, 2011 10:09 AM | Report abuse

Great analysis, Matt. I think those "warm" winters of the 90's aren't going to be seen again for a while. As cold as this past December was, December 2011 could be even colder (basing that on the Pacific being in it's cool phase now).

Posted by: cloudking | January 24, 2011 11:01 AM | Report abuse

Yeah, it wasn't my imagination. Last month was &%#@*!& cold.

Posted by: FIREDRAGON47 | January 24, 2011 11:04 AM | Report abuse

Thanks cloudking. The reason I think we have turned a significant corner is that despite major Pacific events that usually give us warm winters here (last year we had a strong El Niño and this year a strong La Niña), we are getting impressive blocking patterns and cold air transport. I worry what will happen when we actually do get a Tropical Pacific pattern that favors cold around here.

Posted by: MattRogers1 | January 24, 2011 11:12 AM | Report abuse

Correct, FIREDRAGON47. Although I am sure snow lovers will tell you it was too warm and "not how winters used to be around here".

Posted by: SouthsideFFX | January 24, 2011 11:13 AM | Report abuse

i went to my crazy, global-warming-denying in-laws (whom i dearly love and wouldn't trade for anything) last night. remember how it was pretty cold last night? well, maybe it was that and the fact that they were watching the steelers/jets game with temps in the teens and dropping when i came in, but, sure enough, i got the "how's that global warming working for ya, walter" greeting, with laughs all round... sigh...

i explained how 2010 was arguably the warmest year on record, and how the temperature at one's own house doesn't reflect global temperatures etc, etc. surprising how often people extrapolate from local to global temps.

so, following that thought, does this analysis of "cold decembers" extend/apply to the east coast, the united states, north america, the northern hemisphere, the globe?

Posted by: walter-in-fallschurch | January 24, 2011 11:13 AM | Report abuse

Kinda surprised that 1976 was a relatively balmy 35.5 and only 10th on the list - I remember that winter - at least the first half - was absolutely brutal temp-wise

Posted by: hohandy1 | January 24, 2011 11:21 AM | Report abuse

Walter, I love the NWS rankings that they do and here is their latest for December. For Georgia and Florida, it was their coldest December on record (100+ years!). But, New Mexico was the 2nd warmest on record!

Posted by: MattRogers1 | January 24, 2011 11:22 AM | Report abuse

?!?! i don't know any snowlover who wanted december to be any colder than it was... we just wanted the sufficient cold to be accompanied by snow. the cold w/o the snow is lose/lose...

Posted by: walter-in-fallschurch | January 24, 2011 11:23 AM | Report abuse

Dec 1989 was wonderful. Went to the Greenbrier for Christmas that year. Sleigh rides in the snow. Snow on Christmas morning. Frigid temps (way below zero). And then a few days later it warmed up and poof! Winter was over.

Posted by: JerryFloyd1 | January 24, 2011 11:27 AM | Report abuse

I remember Dec., 1989 well...just like today: brutal cold and quite snowy...then winter left for good just after a graupel shower on New Years Day, 1990!

It might be interesting to chart the SNOWIEST Decembers.

Posted by: Bombo47jea | January 24, 2011 11:29 AM | Report abuse

interesting map, matt. looks like the heavily-populated areas, including my in-laws' houses, were pretty cold. i bet just about all of canada would show up w/near-record warmth.

Posted by: walter-in-fallschurch | January 24, 2011 11:34 AM | Report abuse

matt, i addressed my first comment to jason because he put that first comment up there, so i assumed he wrote the article. i see now it was you...

Posted by: walter-in-fallschurch | January 24, 2011 11:36 AM | Report abuse

Any idea/estimate what the Wednesday weather will produce in Garrett County around New Germany State Park? Thanks

Posted by: igbrownlee | January 24, 2011 11:37 AM | Report abuse

Matt - I love this type of answers those random nagging questions weather-freaks like me have in our heads from time to time. Btw, Reston, VA hit 6 degrees this morning...I wonder how Jan will compare to over years, this winter.

Posted by: parksndc | January 24, 2011 11:40 AM | Report abuse

Have we switched our "normals" to reflect the period 1980 to 2010, rather than the period 1970 to 2000? If and when we do, they should reflect the milder, more recent years and the "normals" should go up a bit.

At some point, our normal high for Janaury was 36.5, but due to many cold winters in the 70s and 80s it dropped to 34.9.

National Airport readings seems to be a couple of degrees too warm at this point. We had a similar problem around 1980, which eventually was corrected.

During a windy day, National should not always be 3 degrees higher than Dulles, Andrews, BWI, etc.

Posted by: frontieradjust | January 24, 2011 11:49 AM | Report abuse

Yes, Walter, Eastern Canada was warm in December:

Parksndc, thanks very much. January isn't running as cold so far here in DC (compared to Jan normals), but nationally it is, so I will be curious to see how it ranks too.

Posted by: MattRogers1 | January 24, 2011 11:53 AM | Report abuse

Frontieradjust- I have heard that the normals will be switched at some point this guess would be late spring. But you're right, removing the 1970s will really adjust those normals warmer around here.

Posted by: MattRogers1 | January 24, 2011 11:56 AM | Report abuse

boy, matt, looks like they don't even have red dots big enough for all that canadian warmth... the 5C dot in the legend is smaller than the dots over eastern canada.

why do they take "normals" over a 30yr period? why not make it over as long a period as possible?

Posted by: walter-in-fallschurch | January 24, 2011 11:59 AM | Report abuse

Walter in Falls Church,

There is a worthy contrarian point of view with respect to global warming. If nothing else, the hockey stick has not materialized and is actually pointing south for the past couple years.

I would suggest that you check out Steve Goddard's site. If you google under Steve Goddard, Real Science it should lead you to his site.

Goddard apparently is a climate scientist who is always posting contrarian points of views. While I am not a scientist myself, I believe he is legit.

Posted by: frontieradjust | January 24, 2011 12:00 PM | Report abuse

Walter - we don't want a longer period or else our latest numbers won't effect long-term average by a significant portion. While we can use long-term averages, the most recent numbers will barely BUDGE our "average" unless we limit how many numbers we are averaging.

The more you add to the sample, the harder it is to move a long-term averaged sample. Does this make sense? We don't want to completely flatten the average nor do we want to discount recent numbers from moving the needle. It is a way of both averaging numbers to flatten out some of the "noise" but also keeping the average mobile enough to really see how it is/is not moving.

I hope this helps. I can keep giving you more and more explanation but not sure it would be clearer.

Posted by: Camden-CapitalWeatherGang | January 24, 2011 12:13 PM | Report abuse

i appreciate the comment. i will check it out. my in-laws (whom i dearly love and enjoy spending time with...), are still in the "oh it's not warming" stage - i.e., true denial. there are conceivably valid arguments along the lines of "we don't know the consequences" and/or "is it worth the $ to deal with it?" etc, but my in-laws aren't there yet.

they're at the "little ol' humans can't affect big ol' earth's climate" stage.

Posted by: walter-in-fallschurch | January 24, 2011 12:14 PM | Report abuse

re: Steven Goddard

I've found major flaws in some of his work before (related to snow cover) and I think he has a contrarian bias. I'd read his writings with considerable caution.

Posted by: Jason-CapitalWeatherGang | January 24, 2011 12:28 PM | Report abuse

hhhmmm... i totally understand the concept that the longer sample period is the harder it is to "move" its average. i guess i don't understand why you'd want to have the average move.

Posted by: walter-in-fallschurch | January 24, 2011 12:29 PM | Report abuse

Unfortunately, with global warming there has been a lot of embellishment if not outright falsehoods promoted by both sides. My point is to keep an open mind and be careful before buying into the propaganda. There is an awful lot of money at stake.

Posted by: frontieradjust | January 24, 2011 12:54 PM | Report abuse

I agree about Goddard. He has a tendency to get very defensive when he is wrong and is impossible to correct at that point. He was kicked out of WUWT which takes some doing for a skeptic author.

Walter, for your relatives I suggest a new strategy: find out where they agree about things like saving energy (for future generations), smart grid, renewables like wood heat (ahhhh), preparation for disasters (e.g. dams for water control), etc. It is going to be hard to disagree with common sense, conservation (if they are truly conservative), using nature to benefit mankind. You can point out how cheap wind power is (land based, not off shore) and other facts like that (Texans aren't stupid). If you get agreement on those things, there's no need to discuss motives.

In my own case I just point out to my relatives in New England that it is below zero, that's a lot simpler.

Posted by: eric654 | January 24, 2011 1:13 PM | Report abuse

frontieradjust -

"There is a worthy contrarian point of view with respect to global warming. If nothing else, the hockey stick has not materialized and is actually pointing south for the past couple years."

What on earth are you talking about? Global warming refers to GLOBAL warming - the average temperature on a planet (Earth, in this case). Please check out the yearly averages at the NASA site:

I'm giving you the main page because there's lots of good stuff on there. But if you click on the graph in the upper right, you'll see the yearly average, of which last year was either tied with 2005 or slightly higher - depends on factors which are in the noise, and not very important really.

There is nothing about that graph that even vaguely implies any leveling off. You will of course see noise superimposed from year to year on top of the overall upward trend - due to solar variation and other minor factors.

Walter in FC might want to share this graph with his in-laws.

Posted by: B2O2 | January 24, 2011 1:30 PM | Report abuse

thanks eric,
find common ground... i'm thinking...

Posted by: walter-in-fallschurch | January 24, 2011 1:33 PM | Report abuse

Daggone global warming is freezing my buns off!

Posted by: ZZim | January 24, 2011 2:10 PM | Report abuse

I prefer the HadCRUT global data set because they don't change it constantly "to fit the curve". It shows the leveling off since the late 1990s (which also better matches the two satellite data sources).

Posted by: MattRogers1 | January 24, 2011 2:19 PM | Report abuse

walter-in-fallschurch, please listen to your elders and stop drinking the kool-aid. It's time to grow up.

Posted by: DCer1 | January 24, 2011 3:02 PM | Report abuse

Of course, if it really were carbon dioxide alone that was causing the change (the concept that one profiteer was pushing a few years ago), it could only cause temperatures to go up.

When you are in a greenhouse, it is always colder outside.

Posted by: JustJoe3 | January 24, 2011 3:03 PM | Report abuse

Those numbers for the last 30 years were pretty much consistent with the rest of the mid-Atlantic and out to Ohio.

Posted by: BurfordHolly | January 24, 2011 4:23 PM | Report abuse

It's getting WARMER! Leo Dicaprio told me so!

Anyone who denies it is getting warmer is a HATER!

Posted by: pgr88 | January 24, 2011 4:27 PM | Report abuse

Article Jerry linked in the other thread about the "Arctic fence" contains a few extra facts and is missing others. They mention "Despite cooling from La Niña, newly compiled figures show that 2010 was among the two warmest years in the historical record." The first 6 months were the continuation of El Nino. That should obviously be mentioned since it set the stage for the heat waves they talked about.

They say "Bloggers who specialize in raising doubts about climate science have gleefully pointed to the recent winters in the United States and Europe as evidence that climatologists must be mistaken about a warming trend." Not serious ones. The serious critics point out that climate models predict the opposite: a more positive AO. As long as this trend continues it is the climate models that are in question, not the warming trend.

Posted by: eric654 | January 24, 2011 6:50 PM | Report abuse

What does WUWT mean? Why was Goddard kicked out?

Why are there multiple ways to measure the global temperature, some showing an uptrend and others almost a downtrend?

I'm all for conservation and alternative energy. But I don't like scare tactics based on predictions that may not be panning out.

Posted by: frontieradjust | January 24, 2011 6:56 PM | Report abuse

i always felt the "no warming since 2000" argument is an artifact of the incredibly warm 1998. it would be almost like saying, "boy, snowfall totals around here have really dropped since the 2009/10 winter."

smooth that 1998 year out and the graph pretty much keeps it's upward trend. also, almost all the values from the 2000s are higher than almost all the values from the 1990s... and, look at how anomalous 1998 was, and then consider that it only took about another 7 and another 5 years to get other readings nearly that now we're left to discuss whether 1998, 2005 or 2010 is the hottest year on record.

W(atts) U(p) W(ith) T(hat) is a sceptic website run by skeptic anthony watts. there are no trends (i know of) that show a downward trend - certainly none long enough to be any kind of a statistically significant trend.

"When you are in a greenhouse, it is always colder outside."

it is always warmer on earth than it is in outer space... you do know it's not really like a greenhouse's glass enclosure, right?

Posted by: walter-in-fallschurch | January 25, 2011 6:46 AM | Report abuse

Walter, I agree with you that the last decade has seen the warmest conditions per various data sets and 1998 is skewing the data as you suggest. But if you take a look at the predictions from various IPCC reports, we should see a stronger increase in global temps than what we are currently seeing. This disconnect is only going to get worse due to the PDO switch (which leads to more La Niña events and their impact on cooling global temps as what just started impressively just last month).

Posted by: MattRogers1 | January 25, 2011 7:04 AM | Report abuse

DCer1, you said,
"...please listen to your elders and stop drinking the kool-aid. It's time to grow up."

ha! hardly. it's time for you to get your head out of the sand. it's time for you to get your head around the fact burning co2 has consequences.

Posted by: walter-in-fallschurch | January 25, 2011 7:18 AM | Report abuse

Walter, to show you what I mean, look at this projection from IPCC AR4 2007:

Dec 2010 came in at +0.4C on NASA and only +0.2C on the Hadley data. Let's err to the warmer side and look at +0.4C on the chart's axis and then track across to 2011. Notice it is much closer to "Year 2000 Constant Concentration" than any other projection. Now everyone can agree that CO2 concentrations are currently nowhere close to 2000 levels.

Notice the slope of the other projections. We will need to get moving fast to "catch up" to them. I bet 2011 comes in at or COLDER than the 2000 constant concentration forecast.

Posted by: MattRogers1 | January 25, 2011 7:30 AM | Report abuse

When I look at graphs of global mean temperatures, I see 1998, 2005 and 2010 as the warmest years. I believe 1998 was the record El Nino and an outlier. If you ignore that year, what the record shows to me is a warming up to 2005 and then leveling
off for 5 years. If one looks at the curve,
one sees similar periods in the last 30 years.

Carbon dioxide is not the only forcing. There is natural variability, which we do not know well, partly because we have truly global data only for 32 years and that period is contaminated by significant anthropogenic forcing. There are other greenhouse gases, aerosols, changes in land use and changes in solar output. As Kevin Trenberth said, we don't have good enough data to explain year to year changes.

Global warming is based on the results of quite complex models. What is Matt Rogers forecast for 2011 based on? I do not think we know enough about the Pacific Dedacal Oscillation to know what it will do and how strong it will be in the next year.

People who say "Global warming is not occuring" are in my opinion wrong, but not haters.
People who say "global warming is a hoax"
are making a very serious accusation that I resent strongly.

Global warming is a long term trend. A single month is not the correct way to assess it.

Posted by: Dadmeister | January 25, 2011 10:14 AM | Report abuse

matt. that's showing projections out 100 years from 2000. we're 1/10th of the way from the middle of that graph to the end at 2100. it's hard to tell where .4 or .2 are on the graph. maybe i'm not understanding that graph.

are you basically saying it's not warming fast enough? or as fast as predicted?

or pointing at the trend of the last say 10 or 15 years? or of just last december? t's funny because i bet one could choose a certain time scale to prove anything...

i think that noaa page with the dots ( ) would say every month in 2010 was above the 20th century average, and in fact that every month for the past 25 years has been above that average....

i find that truly amazing. 300+ above average months in a row... eric complains about the "20th-century average" being too low, and promises, like you, la nina and some oscillation will bring us a cold month or two...

we'll see.

Posted by: walter-in-fallschurch | January 25, 2011 10:33 AM | Report abuse

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