The perpetual west coast ridge and central/east coast US trough continue to hold fast, but some changes in the upper-level pattern over Russia will begin to affect things downstream leading to a retrograde of the amplified pattern. The cold arctic air has continually been sliding just east of us on the other side of the Rockies but it looks to reach WA this time as the trough retrogrades and a positively tilted short wave provides the offshore oomph aloft to help push the arctic air west.
The strong polar jet over eastern Russia is beginning to split into a northerly and southerly branch (a sign of spring). The ensembles all have the northern branch, with a strong embedded 150+knot jetlet, take a trip over Alaska and dive south along the west coast. This feature helps retrograde the North American trough and supports a positive tilt short wave impacting WA Friday .... all ensemble support this feature, although the magnitude and timing is slightly different from run to run.
Friday night there is high probability that an arctic front will pass south through the Fraser river gap. Moderate chilly winds will arrive Friday night but last only a day or so.... the air won't be that cold, but there is possibly a chance for a flurry or two Friday night around Skagit/Island counties and possibly along the northeast of the Olympic peninsula.
A second short-wave arrives Monday night and may be more interesting ... several of the ensemble runs and the ECMWF support a quick pulse of arctic air.. a bit colder and a bit more lift/moisture than the first feature. However, ensemble spread is higher for this feature.
Both of these features are rather weak for an 'arctic blast' event and are quick lived ... the air won't be that cold (it's almost March!) and the pressure gradients aren't too extreme. However, both could result in a period of gusty winds in the NW interior especially in W Whatcom County, and possibly some light snow along the frontal boundaries and north Olympic peninsula.
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