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February 2015
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Shifting Patterns

Posted: February 2nd, 2015

 

Long-range upper level forecast (GFS). Note arctic air in blue over the Gulf of Alaska... Let's keep our eye on that.

Long-range upper level forecast (GFS). Note the arctic air in blue over the Gulf of Alaska… Let’s keep our eye on that.

 

We’ve got a wet week ahead of us. The ridge of high pressure that has been dominating our weather, keeping us relatively dry all season, was knocked down over the weekend by a large low pressure system offshore. Unfortunately for mountain snowpack, freezing levels are expected to remain relatively high through the weekend.

 

The first wave associated with the aforementioned large low passed through the region this morning. For a little while, right around 8:00 AM, it got exciting when radar reflections generated a RainWatch forecast alert. After two hours, though, the most rain that had fallen was only 0.25 inches, which is well short of statistical significance. That said, the shower invited 9 drainage-related calls in three hours.

 

Additional waves are forecast to pass through tomorrow and Wednesday. By Thursday and Friday, a stronger, more organized system is expected to work inland and provide the City and mountains with rainfall amounts, while not too impressive, unseen in weeks. And while forecast models are in general agreement with respect to the overall pattern, the NWS has been emphasizing difficulty around timing.

 

Additional rainfall looks likely next weekend, though we’ll see whether or not the atmosphere tries to rebuild high pressure. Models are curiously showing arctic air pooling over the Alaskan Gulf next week, which depending on its strength and position could bring about another big, ideally colder but probably just drier, shift in the pattern.

 

NWS Area Forecast Discussion
NWS Forecast Table Interface—Seattle
NWS Forecast Table Interface—Tolt Reservoir
NWS Forecast Table Interface—Chester Morse Lake
SPU Water Supply Outlook

 

JRH