December 18th, 1990 Snow Event

Also known as the Arctic Express, Mother of all Convergence Zone's and Seattle's December Blizzard.  This storm was not only my first most vivid memories of any weather event but probably one of the biggest influences on why I am so interested in weather today.  I never wish property damage, injury or death to anyone, however, I would love to observe a storm like December 1990 again as an adult where I am more capable of documenting and photographing such an event.

Heaviest snow fall I've ever witnessed started at about lunch time on this day.  I could be wrong but if memory serves 8 inches fell within a half hours time.  After that we had lighter snow fall for the rest of the afternoon.  Near as I could tell there was a little over a foot of snow when I left school, I remember it coming all the way up to my knees (I was a little boy at the time.)  When I had gotten home from school that afternoon the power was out, and it didn't return until mid day the next day.  I remember just after it got dark that there was a bright flash and a very loud thunderclap, snow was coming down pretty hard again during this time.  As darkness completely fell I wasn't able to tell from inside if it was still snowing because the power was out everywhere around us, no street lights or porch lights to watch for falling snow under.  It was an early start to the school districts winter vacation and the ground remained covered in snow until it was time to go back to school after New Years Day. 

Stories and photos from the storm are difficult to find and I've noticed particularly out of all the news articles I can dig up, like with many events, The then unincorporated King County, (Shoreline School District) now City of Shoreline was largely left out of the picture.  I've been unable to find what the snow depths were or any other details other than based on my own memory as a child.

My own artwork inspired by the December 1990 snow, created 1997.

One thing I haven't been able to find at all, is a surface analysis map of the region on December 18th, 1990, around noon time.  Everything I've read and researched says it was a Puget Sound Convergence zone storm, biggest one probably ever observed by modern instrumentation.  All the stories go, that a cold air mass in British Columbia moved closer and closer to the US border, when during the afternoon the cold air rushed into the Puget Sound generating a convergence zone.  Such convergence zone would not be the conventional kind where Westerly wind moving around the Olympics meets in the middle of the Puget Sound, but instead a convergence of warm moist air to the south colliding with the cold arctic air pouring into the Puget Sound.  We had a similar but not nearly as strong convergence in December 21st, 2008. 

I can only imagine right now that in order to generate that pattern you would have to have a strong high pressure over Western Canada with a deep low pressure sliding south off the coast of Western Canada and Washington before changing into an eastern direction just south of the Puget Sound or through Oregon.  A similar situation was occurring in December 2008, however the pressure gradients were not nearly as strong or in quite the same directions and paths.

Was it really a blizzard?  The current criteria for a Blizzard is falling snow, with winds exceeding 35mph gusts causing a reduction in visibility to less than a quarter mile, for 3 hours or longer.  We had winds gusting to 50-70mph, after the heaviest snow had already fallen, was it still snowing?  Hard to say due to blowing snow but I do remember visibility being cut down quite a bit.

Temperatures started in the low 40's in the morning and then quickly dropped to the low 20's in the afternoon as the snow started falling.  Temperatures at Sea-Tac (Not Shoreline) never broke freezing again until Christmas Day.  Lows ranged in the teens with highs in the mid 20's.  After December 25th another surge of arctic air blew in and resulted in a wider spread snow storm for the region before everything begin to thaw starting around New Years Day.

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One of my goals with this blog, is to have all of the major arctic or snow events, documented in one place that has occurred in the greater Seattle area, in an effort or attempt to identify any patterns associated with the snow events.  I suspect it's actually several global patterns and local patterns combined that make the perfect recipe for a snow disaster for this region.