Monday, January 30, 2012

Brrrr: Arctic Oscillation Goes Deeply Negative, Here Comes Winter

Following up on Jan. 9's "Dear Europe: Arctic Oscillation About to Go Negative, Try to Stay Warm".
Here are the latest index values from NOAA's Climate Prediction Center:
Observed Daily Arctic Oscillation Index.

And here are some of this morning's British headlines"
Telegraph:
Big freeze to hit Britain as temperatures plummet to -10C
Daily Mirror:
UK weather: Temperatures set to plummet to -10C this week as parts of Britain wake up to snow - pics 

You don't know where the Arctic 'fence' will open and the timing is always iffy.
If the gates were to open over the U.S. Northwest all that -50F air over Fairbanks would come spilling into the contiguous Lower 48.

Here's the quick tutorial from the Jan. 9 post:

Arctic Oscillation: positive phase (left) has higher air pressure in mid-latitudes than in Arctic, leading to milder winter for US; negative phase (right) has higher air pressure over Arctic, pushing frigid, wet air into US.: Credit: NASA. 
Arctic Oscillation: positive phase (left) has higher air pressure in mid-latitudes than in Arctic, leading to milder winter for US; negative phase (right) has higher air pressure over Arctic, pushing frigid, wet air into US.: Credit: NASA.Technically, the Arctic Oscillation is a measure of atmospheric pressure variations at sea level north of 20N latitude. Where an Arctic high develops affects weather thousands of miles away....

Finally:
Here are the ensemble model runs at NOAA's Climate Prediction Center.
For a major change the index has to go below and stay below the zero line for at least a few weeks

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/ao.sprd2.gif