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The Arctic Oscillation

The Arctic Oscillation refers to opposing atmospheric pressure patterns in northern middle and high latitudes.
The oscillation exhibits a "negative phase" with relatively high pressure over the polar region and low pressure at midlatitudes (about 45 degrees North), and a "positive phase" in which the pattern is reversed. In the positive phase, higher pressure at midlatitudes drives ocean storms farther north, and changes in the circulation pattern bring wetter weather to Alaska, Scotland and Scandinavia, as well as drier conditions to the western United States and the Mediterranean. In the positive phase, frigid winter air does not extend as far into the middle of North America as it would during the negative phase of the oscillation. This keeps much of the United States east of the Rocky Mountains warmer than normal, but leaves Greenland and Newfoundland colder than usual. Weather patterns in the negative phase are in general "opposite" to those of the positive phase, as illustrated below.

Over most of the past century, the Arctic Oscillation alternated between its positive and negative phases. Starting in the 1970s, however, the oscillation has tended to stay in the positive phase, causing lower than normal arctic air pressure and higher than normal temperatures in much of the United States and northern Eurasia.

Spec8472 wrote:If this year is like last year, it'll be a very cool Christmas - probably 25C or so.
Which is very odd, because it's normally up around the 35C mark.

Winter? No, it's Summer for half the planet, thanks.

Spec8472 wrote:If this year is like last year, it'll be a very cool Christmas - probably 25C or so.
Which is very odd, because it's normally up around the 35C mark.

Winter? No, it's Summer for half the planet, thanks.

kal wrote:that makes me want to fly south for the winter

boballab wrote:Actually what you are experiencing is not that funky, it is just what happens when the Arctic Oscillation (AO) goes positive. Last year at this time the AO was negative which allowed very cold arctic air to drop much further south.

GBLW wrote:

boballab wrote:Actually what you are experiencing is not that funky, it is just what happens when the Arctic Oscillation (AO) goes positive. Last year at this time the AO was negative which allowed very cold arctic air to drop much further south.

I'd say it's a bit more than AO - since it appears that Canada's arctic sea ice is the least on record for MANY years -
http://www.cbc.ca/news/technology/story ... -loss.html
and recently -
http://www.cbc.ca/news/interactives/map ... e-regions/

As for the weather locally, it's a bit warmer than normal and we're not having quite as much rain as we usually do. Of course last year at this time we were starting to worry about not having any snow at all for the winter oh-limp-ix.

The whole problem is we base our expectations on climate - only what we have to live with is weather.

kp

November 2, 2011
A rapid freeze-up
Arctic sea ice extent increased rapidly through October, as is typical this time of year. Large areas of open water were still present in the Beaufort and Chukchi seas at the end of the month. The open water contributed to unusually warm conditions along the coast of Siberia and in the Beaufort and Chukchi seas.

Atmospheric conditions
In recent years, low sea ice extent in the summer has been linked to unusually warm temperatures at the surface of the Arctic Ocean in the fall. This pattern appeared yet again this fall.

Air temperatures over most of the Arctic Ocean for October 2011 ranged from 1 to 4 degrees Celsius (1.8 to 7.2 degrees Fahrenheit) above average, measured at the 925 millibar level, about 1,000 meters or 3,000 feet above the surface. However, over the eastern Canadian Arctic and Greenland, temperatures were as much as 3 degrees Celsius (5.4 degrees Fahrenheit) below average.

These temperature anomalies in part reflect a pattern of above-average sea level pressure centered over the northern Beaufort Sea, and lower than average sea level pressure extending across northern Eurasia. This pattern is linked to persistence of the positive phase of the Arctic Oscillation through most of the month. These pressure and temperature anomalies tend to bring in heat from the south, warming the Eurasian coast, but they also lead to cold northerly winds over the eastern Canadian Arctic Archipelago. However, along the Siberian coast and in the Beaufort and Chukchi seas, warmer temperatures came primarily from the remaining areas of open water in the region, as heat escaped from the water. These effects are more strongly apparent in the surface air temperatures: average October temperatures in the region were 5 to 8 degrees Celsius (9.0 to 14.4 degrees Fahrenheit) above average.

December 5, 2011
Winter in the Arctic: Ice and storms

Northern Hemisphere snow cover
The positive phase of the Arctic Oscillation also tends to be associated with unusually warm conditions over Scandinavia. According to Sweden's meteorological office, the country's average temperature for the month of November so far was 7 degrees Celsius (12.6 degrees Fahrenheit) above average. Typically by November, much of Scandinavia is already covered with snow, but maps from the Rutgers University Global Snow Lab show that snow cover levels were anomalously low over Scandinavia and northwestern Europe during November. Below-normal snow conditions were also evident over most of the continental United States, except for the northern Rockies.