Winter '10 / '11 - North Atlantic Oscillation at Winter/s Crest

Meteorological winter has reached the half-way mark.  Coldest time of the year in the Northern Hemisphere...yet for much of the first half...temperatures have been much below normal...an unexpected oddity during la Nina.

This Hovmöller diagram from CPC shows the 5-day running mean of 5H anomalies above 65°N.

The strong action center along 60°W shows strength and persistence of the NAO over the past 90 days. 

The blocking HIGH over Greenland has weaken in recent days with a subsequent rise in the index to minus 2...heading for positive territory this weekend.

NAO is forecast to fall below zero later in the week as the PNA index rises to about 3...suggesting a favorable environment for coastal storms to develop off the SE coast.