Monday, December 6, 2010

Can We even Dream of a Warm Christmas?

It is hard to think warm when I saw solid ice on a road in Durham at 1:30 PM today.  Winter's featuring La Nina often start off cold in the Eastern US and Western Europe but this season is definitely a bit extreme.  Great Britain and Ireland are covered in snow!  Recent Satellite photos would make one believe that the two islands used to moderate winters are in an Ice Age.

Great Britain and Ireland are reliving the Little Ice Age
Source: NOAA Earth Observatory
Portions of NC and VA enjoyed an early season snow this past weekend.  Deeper than expected cold allowed a relatively dry system to cover grassy areas with a coating to 2".  I had expected an early season snow by the end of November and was 4 days late.  The question now is whether this La Nina winter will actually behave like most of them and warm up for the holidays and much of January.

In my previous article I mention the potential monkey wrench to a warm Christmas being seen by computer models in the re-forming of a North Atlantic ridge of high pressure and movement into the -NAO region.  Unfortunately that is not off the table.

Out in the Pacific and Siberia models are forecasting weaker versions of the -EPO and -WPO.   The EPO is known as the East Pacific Oscillation.  It's negative phase features trough NE of Hawaii which ultimately leads to an Eastern US trough.  The WPO is the West Pacific Oscillation.  It's negative phase is freezing us right now with arctic air.  A -WPO is a bubble of high pressure in East Siberia which shoves Arctic air over the Pole into our hemisphere.  Here are the forecast values:
Even a weak -EPO is not a warm sign.
WPO is forcast to continue strongly negative.
Source: NOAA Earth Science Research Laboratory

Global Forecast System (GFS) Ensembles provide 12 possible outcomes for Dec 22 (Day 15).  None of them look particularly warm, some are pretty cold.  Could it warm up in the 3 days leading up to Christmas?  This year could feature my most difficult holiday forecast ever because of how small deviations in jet stream and storm tracks can mean big weather differences.

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