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THURSDAY MARCH 29 - NORTH ATLANTIC OSCILLATION: PART 2
Last night I introduced the North Atlantic Oscillation, or NAO. This cycle has
two extremes, called the
negative phases. Research has shown that
when the NAO is in its negative phase, there's a greater chance of cold and snow
in the East. Here's why.
negative phase, the high altitude winds that
move weather systems across
the Atlantic Ocean tend to be relatively weak, and the jet stream pattern tends
to have lots of dips and bends in it. The weaker winds mean that cold air in the
Eastern U.S. doesn't move out to sea very quickly, keeping the chill on land. The
wavy jet-stream pattern tends to promote stronger storms. So colder air plus a
tendency for strong storms means more potential for snow.
graph showing the NAO the last couple months.
Times when our area got at
least one inch of snow are marked with a snowflake (*). It's far from a perfect correlation,
but in general the snowy times tend to occur when there’s a negative value of the NAO.
So if we can predict the NAO, it's at least a heads-up to forecasters for times to be
especially watchful for snow. I promise, you'll be hearing a lot more about the NAO in
winters to come.