Monday, February 27, 2017

WeatherWatcher: Winter Weather Advisory extended until Tuesday 4am

The National Weather Service in Seattle has extended the winter weather advisory issued Monday morning all the way into Tuesday morning at 4am.

They are forecasting another 1-3 inches of possible snow on hills 300 feet and above. Again, this is showery weather with a hit or miss pattern, some locations may receive nothing.

As of 9:30pm Monday evening an active convergence zone has set up. According to radar the east-west band of precipitation extends from Lake Union in Seattle as far north as Alderwood Mall in Lynnwood. Shoreline appears to be seeing spotty locations of snow, rain and snow mixed, or light rain at this time. Some precipitation might be evaporating before it reaches the ground.

Given the stable location of the convergence zone I expect that it is possible over night as temperatures cool slightly for a changeover to snow with accumulations especially at the highest points of Shoreline and Lake Forest Park. I'm calling this event a 50% chance of accumulation, in other words there is also a 50% chance of no accumulation. If accumulations occur some rare spots could see even as much as 4 inches of snow.

Bottom line: Impacts are mainly limited to travel challenges and if accumulations are in the higher end there could be some localized power outages. This remains a marginal snow scenario with temperatures struggling to cool below freezing in most places, which means the snow (if any) will be in a constant state of melting more or less.

Forecast: We are expected to warm finally Tuesday afternoon to transition to just rain showers. Tuesday evening winds are picking up for a possible wind storm, not a major one, but at this time we are looking at gusts as high as 40 mph. Temperatures are expected to remain in the mid 30's to low 40's. Steady rain is expected as well but amounts are expected to be light. Rain continues through Friday afternoon with showers returning Friday night and through the weekend.

Longer range: There are new indications now that a surge of arctic air might make its way near or into the region creating a renewed threat of at least some rain and snow mix next Sunday evening, again. This is still fairly far out and models are being vastly inconsistent at this time. I'll be updating as we get closer to that situation.

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