Monday, March 18, 2013

Why is the Winter Pattern Lingering So Long?

This is the most asked question over the last week or so of northern Ohio residents. March of 2013 is the polar opposite of March of 2012 when we had a handful of 80 degree days en route to the warmest March in 140+ years of record keeping.  So far this March (through the 17th) temperatures rank 67th coldest---right in the middle of the 142 years of record keeping.

I only have a few minutes this morning due to the winter precipitation moving through the area along with my multiple weather segments so I'll keep my analysis brief:

The answer lies within the 3 major indices that govern our patterns. The AO (Arctic Oscillation), the NAO (North Atlantic Oscillation) and the PNA (Pacific North American Pattern). Last winter (2011-12) I wrote an extensive explanation on these three teleconnections. You can read it here.

Each index plays a different role at different times of year. In the summer, many of these indices are not as strong. But in March, they can play havoc with the development of spring warmups. The Sunday we had recently with temperatures at 70+ was the one bright spot in this colder than normal pattern.

Recently, these indices that measure the strength of arctic storm patterns (AO, NAO) are strongly negative which mean colder than normal. (graphic courtesy: Dr. Ryan Maue)

The PNA (pacific north american pattern) has been trending positive. All of these keep the NW flow aloft firmly entrenched keeping temperatures well below normal across the eastern US.

Not to worry. The "nickel-and-dime" cold punches WILL some point :)

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