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Wednesday, November 24, 2010

Broken crystal balls

Not all weather forecasting relies on sophisticated computer modeling. Sometimes it's just a matter of simple pattern-recognition. You see this particular set of variables together and the next day you have this particular weather; multiple repetitions of the pattern becomes a trend. A few subsequent successful predictions based on that trend, and the correlation becomes canon, more or less.

A shining example of this is a model which has been used to successfully predict major snowstorms in the Salish Sea basin. I first heard of it from my wife, who at the time was an undergrad at UW; she had come up with it on her own through simple observation over one season of especially frequent snowstorms. I then saw it published by NOAA Commander Ken Lilly in the excellent Marine Weather of Western Washington.

The model is this. If you have:

a) a very deep and cold High over central British Columbia

b) a very deep Low marching in just south of the Olympic Mountains and

c) the jet stream sitting right over the Columbia River

then you are setting up for a very substantial snowstorm.

Over the past 20 years I've watched this pattern play out many times. More importantly, I have not seen a major snowstorm develop here without these parameters.

On Sunday night, we didn't meet any of these parameters. We expected the arctic blast, we didn't expect the snow. This week's weather changed the model. A lot of people will be poring over a lot of data gathered this week and developing new models from it for better prediction in the future. Is this week's storm, as some media outlets have suggested, a symptom of global climate change? Possibly. More on that topic later today.   

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