WeatherWatcher: Winter Storm Watch issued, Forecast

Sunday, January 12, 2020

Snow at the top of motorcycle hill (NE 185th ST and 12th Ave NE.
February 2019, Photo by Carl Dinse


Winter Storm Watch: The National Weather Service in Seattle has issued a winter storm watch in effect from Sunday afternoon through late Sunday night.

  • What: Heavy snow possible. Total snow accumulations of a trace to 2 inches possible, some areas could see up to 5 inches.
  • Where: Seattle, Everett, Tacoma areas, this includes Shoreline and Lake Forest Park.
  • When: Sunday afternoon through Sunday night.
A winter storm watch means there is a potential for significant snow, sleet, or ice accumulations that may impact travel.

Forecast: As you may have gathered, since there is a winter storm watch in effect, snow is certain in the forecast. How much snow is still uncertain even less than 24 hours away. The reason for this uncertainty? the Puget Sound Convergence zone. Models are having a hard time pinning down how strong it could get, and how fast or slowly it could move. 

Right now most models are indicating the areas from Everett to North Seattle could pick up around 5 inches of snow, maybe even 7 inches of snow if it gets really intense. 
Past convergence zones have been known to surprise forecasters and computer models by dumping anywhere from 6 inches of snow to 14 inches of snow when only 1-3 inches of snow or no snow at all was expected.

I know of several examples of convergence zones that were not forecasted until they were on top of us and left us buried in 6-8 inches of snow. April 2008 was one of them, December 18, 1990 was another, and I can remember one in the mid 90's as well that brought us 6-7 inches of wet snow. All three of those events were not forecasted at all until after the snow started falling, and then the accumulations were always underplayed. 

A second uncertainty is how cold it will be before the arctic front moves south. It could be cold enough during the day Sunday for some areas to see snow before the arctic air mass moves in, which could easily add a couple inches of wet snow accumulation before the freeze.

Here's what we can generally expect on Sunday: Breezy south winds, gusting to 35mph. Rain at times, up to a half inch of rainfall is possible. Around 2-4 pm in the afternoon the cold air should be passing through Shoreline and Lake Forest Park. Sometime in that transition or a little before that transition the rain will change over to snow. 

Winds will calm down as they switch from the south to the north. When the winds are in transition the convergence zone is overhead. Once north winds start getting gusty it'll be the indicator that the snow is heading south and should taper off to snow showers, likely late in the evening. 

When all is said and done, we could be sitting in anywhere from 1 - 7 inches of snow. Slight chance it could be more, but we'll probably stay under the 7 inch mark.

Forecast: 
Monday through Wednesday: Cold, cloudy with a chance of snow the entire period. Lows are expected to be in the low 20's, to upper teens, with highs near 30. Monday night or Tuesday morning is expected to be the coldest night.

Wednesday evening our next storm moves in, with increasing snow. Models are still not making up there mind but the latest runs seem to average another 5 - 6 inches of snow from this storm before it ends on Thursday or Friday. Temperatures are also a little inconsistent, we are not sure that some rain may mix in during the warmest periods of the day or not yet.

Right now, next weekend is showing a slight warm up. We are dealing with a lot of uncertainty that far out though so we'll have to wait until the middle of the week to see what it really looks like.


For current weather conditions, advisories, watches or warnings, visit www.shorelineweather.com




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