Winter 2010-11 Roundup Part 2

The question I am most often asked is: Why was everybody wrong about how cold it was going to get?   It is a very fair question because when a person hears the term La Nina and lives in the east the expectation is that most of the season will be mild and dry.  As discussed in part 1, La Nina had far less to do with the winter than the Arctic and North Atlantic Oscillations.

I have a theory based on the late 1970's Ice Age winters that hurricane paths have some correlation to the winter weather pattern.  Last summer's hurricanes roamed the east and Central Atlantic.  There were some impacts on Canada but otherwise out to sea.  Much like Summer 1978. Below is the summer 2010 tropical storm tracks:

Note the paths of long-lived major hurricanes in the West Central Atlantic.

The idea is that the storms carve up the high pressure ridges when tend to dominate the Atlantic by feeding King TUTT (Tropical Upper Tropospheric Trough).  The result is a tendency for low pressure in the Atlantic.  Add the tracks to westerly upper level winds in the tropics (West QBO) and favorable conditions for Negative NAO's and the result is a long lived low pressure region which then leads to cold arctic air flows from the land towards the system.

Image Source: Plymouth State Weather Center.
Upper level westerly winds in the tropics and easterlies in
the high latitudes combine to promote a low pressure area.

Fortunately by mid January the -NAO process began breaking down and pattern became milder (for NC and VA) but there were 2 very serious central US storms and historic Arctic outbreaks.

Now that Winter 2010-11 is now history we appear to continue to be set for a moderate summer which contains serious east coast hurricane threats.  My Summer 2011 preview will be coming soon.

Why February will be more Moderate

Unfortunately we will need to survive a serious Arctic outbreak to reach a warmer and more gentle period of temperatures.  During the past couple of days the Stratospheric warmth over the North Pole has broken down.  This is usually a precursor to a +AO (Positive Arctic Oscillation) and a retreat of the coldest of the cold air back to polar regions.  The lag time in my experience from this breakdown to the effects here in Central NC and VA is 10-14 days. 

Source: NOAA Climate Prediction Center

Do not break out the tanning lotion and shorts just yet.  This time of year the rising sun angle is one of many variables which warm the heights of the Rockies relatively faster than eastern lowlands. This favors a High Pressure system called the +PNA (Positive Pacific North America) which sets up in the Northern Rockies and tends to funnel continental Canadian air towards the south. 

Therefore the Outlook through mid February is expected to be near average (which should FEEL warm) and feature quite a bit of back and forth as fronts come and go.