Friday, April 20, 2012

Warm 2011-2012 winter in parts of US due to NAO, North Atlantic Oscillation -Washington Post

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Too early to say for sure about next winter, but if El Nino forms it could be very cold and snowy.

4/18/12, "Grading our 2011-2012 winter forecast," Washington Post, Matt Ross

(scroll down) "Overall:...

What went wrong this winter? The answer is actually quite simple. The NAO (North Atlantic Oscillation).

A negative NAO, prevalent the prior two winters and one which we favored in our outlook, typically represents high latitude blocking (areas of upper level high pressure), especially near Greenland. This type of blocking usually leads to colder air masses in our region with a greater likelihood of snow events. In the end, the NAO was sharply positive most of the winter, and this led to colder air being bottled up in Canada, and a storm track to our west - typical of a La Nina without blocking.

What can we expect next winter? It is way too early to have much of a clue, but there are some indications that an El Nino might form. El Nino events have led to some of our snowiest winters (and often cold as well), though a snow winter is hardly a lock, especially if other factors such as the NAO work against it. Of course, after this winter, anything will seem cold and snowy by comparison."...via Tom Nelson


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