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Saturday, September 15, 2012

Winter forecast

My wife is wishing for a snow dump in January and February.

Hard to see signs so far. Many are going with a much colder and snowier forecast than normal, others are saying it will be colder and snowier than last year, which doesn't take much.

After an unusually warm and snowless WINTER, its even more unusual to have them back to back. So its an easy forecast to say snowier than last year. Most forecasters are looking at the El Nino and how strong and developed it is forecast to be, but there are two very different solutions using that parameter. Either like last year, or like the year before. Odds say that it cannot be like last year again though I don't believe it will be much like the year before either.

We suffered last winter from a string of mostly positive NAO values. This started in the fall and lasted to March. Positive NAO = warmer and drier. The year prior we had a long string of negative NAO. Below is the snapshot of the NAO today: Note its mostly negative until September. Next is a graphic from an archive last Dec and how the NAO was acting. You can see a fairly back and forth pattern up until October when it stayed positive, mostly, until May. So if you look back at cycles, they are mostly 3 month, but in 2010 we had a prolonged negative NAO, and the cycles stretched to 6 months.

So if it flips positive in September, it is not likely to flip back until late Jan or Feb at the earliest. So based on NAO patterns I'm saying an above average temp until mid Jan when it normalizes and then goes colder in Feb/Mar. Snow is trickier, as our rain has been more severe than frequent. In Nov/Dec, a storm with 2" of precip typically is rain, until the end of Dec.

Next post will address the upper air motions, which resemble last years with highs moving in from the SW instead of the NW.

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