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January 8, 2010

Why so cold? Blame the North Atlantic Oscillation

 Cold, snow in Baltimore

I received this question in a reader comment a little while ago. Seemed like a fair one:

"Why so cold this year Frank?  Jet stream - El nino?  Any indication that it will continue?  Wasn't planning a break but with these temps may break up the winter with a trip to the Keys."

Check before you fly off to the Keys. The forecast there for Sunday calls for a high of 57 degrees and a low of 46. I've been there in that kind of weather. It ain't no picnic.

As for why it's been so cold, I sent the question to Chris Strong, at the National Weather Service Forecast Office in Sterling. Here's his reply:

"The North Atlantic Oscillation is the reason for recent cold. It is a cycle that to a large extent governs how cold we are here at any given time.

"Unlike the El Nino/La Nina cycle which happens over years, the NAO cycles over weeks.  Here is a link to the recent trend on the Climate Prediction Center's webpage...

"However, I would caution that we are grading 'cold' on the skewed scale compared to our relative mild weather over the past several years. A few thoughts:

* November was over 4 degrees above normal (very mild), which will also alter people's impressions going into winter.

* Looking at Dec 1-Jan 7, we are 27th coldest in Baltimore's records with a 33.7 degree avg. 1876-7 was coldest at 26.0 degrees, but more recent colder were 1989-90 27.8 (#3) and 2000-01 at 29.5 (#5).

* December was a few degrees below normal, but was just our 36th coldest on record.

* The first week of Jan has been cold, but as the first week of January goes, it was just the 24th coldest on record.

* Another important temperature records have been broken this winter in Baltimore."

So, maybe it's not so cold, after all. And if it feels cold, just figure the NAO can change over a period of weeks. It can't last forever.

(AP PHOTO/Steve Ruark/Jan. 8, 2010)

Posted by Frank Roylance at 1:36 PM | | Comments (8)
Categories: Phenomena


So this is not slowing down the global warming?

FR: It's a short-term weather cycle.

Frank- somehow a helicopter crashing in Garrett County (presumably from the weather) didn't make the Sun! Here is a link from the Cumberland Times-News.

FR: Thanks!

Although December temperatures weren't extreme, statewide precipitation averages were the wettest on record for Maryland and Virginia.

Why is it so cold? Mainly, because the sun has had less activity in sunspots lately and because of this North Atlanic Oscillation.

This does however make it ABUNDANTLY clear that man has little effect on the climate of the planet, and that we are basically at the whim of what this planet wants to do at any given moment.

The NWS should be embarrassed by the response from LWX.

NAO is an effect...not a cause. The NAO state is a measure of atmospheric pressure differences over two stations in the north Atlantic. It/s an observation.

What caused the cold outbreak was a stratospheric warming event during late NOV / early DEC. This caused the polar vortex to slow...split in two...and reverse direction...creating an anti-cyclonic (clock-wise)circulation aloft. The reversal took about 3 weeks to propagate to the surface...creating HIGH pressure over the pole....which in turn created favorable conditions for arctic outbreaks...such as the one currently observed.

These reversal events occur preferentially during years (such as this one) where an east wind is observed in the tropical stratosphere (quasi-biennial oscillation - QBO) and solar activity (sunspots) is low. Above normal snowfall in eastern Eurasia this fall played a significant role in initiating the stratospheric warming event.

HIGH pressure @high-latitudes are indicated by negative NAO and the Arctic Oscillation (AO). To blame the cold on -NAO is just plain wrong.

Right, only if it is warmer than normal should it be reported it as global warming. If it is colder than normal, report as weather. I'm sure Mann has a paper out explaining that.

FR: Nope. If it's warmer than normal on short time scales, that, too, is weather. Global warming is about the long-term, global trend.

According to Professor Mojib Latif from Germany, eminent climate scientist and leading member of the UN's Intergovernmental Panel on Climate Change, this "short" cold period isn't as short as you might think. It's the beginning of a 20-30 year cooling cycle just as the warming cycle we're now leaving wasn't due to human-caused global warming, but rather to the normal cycles the planet goes through.

FR: You (and the Daily Mail and George Will) are twisting his position. Here's an interview with NPR in which he tries to clarify misinterpretations of his work by GW deniers. He makes it clear he believes GW is and will remain a real issue after any short-term cooling has passed: "However, if we look further, then we have some indications that there are after, say after 2015 or 2020, you know, global warming will accelerate again." Here's the interview:

TQ, I'm not sure where your getting your information from but there was no Major Warming (MMW) in the stratosphere in late November and early December.

But I'll give you the importance of the qbo, sun, and Eurasian snow cover. Don't forget the El Nino as well though.

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About Frank Roylance
This site is the Maryland Weather archive. The current Maryland Weather blog can be found here.
Frank Roylance is a reporter for The Baltimore Sun. He came to Baltimore from New Bedford, Mass. in 1980 to join the old Evening Sun. He moved to the morning Sun when the papers merged in 1992, and has spent most of his time since covering science, including astronomy and the weather. One of The Baltimore Sun's first online Web logs, the Weather Blog debuted in October 2004. In June 2006 Frank also began writing comments on local weather and stargazing for The Baltimore Sun's print Weather Page. Frank also answers readers’ weather queries for the newspaper and the blog. Frank Roylance retired in October 2011. Maryland Weather is now being updated by members of The Baltimore Sun staff

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