Update on the Friday/Saturday Snowstorm

5:40 AM Friday.  Will do a major update at 9 AM.  Currently, a weak band of snow is over NW Washington (light snow is reported at Orcas Is). and a few snow showers approaching the coast..see radar below.  The main show is not until this afternoon.  The morning commute around Seattle will be fine.  I am going to try NOWCASTING later today... frequent updates heavily using weather radar.

5:40 AM weather radar...green are snow showers

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We are now approximately a day out from the beginning of a significant snowstorm of the Northwest and the models are now converging inn their solutions.  As a result, our confidence is now quite high that snow will begin falling earl tomorrow afternoon around Puget Sound, with an earlier initiation to the north, later to the south.

The timing of the snow is critical, since the initiation of snow mid-day might leave folks stranded at work or lead to road grid-lock if everyone runs for home when the snowflakes begin to fly.

The latest model runs suggest that the snow will reach the area by the early afternoon.  The UW WRF model shows the snow just reaching Seattle at 1 PM Friday (2100 UTC)--see below.

With snow over the entire Puget Sound region by 4 PM (below) and will continue through much of the evening.

The  total snowfall through 4 AM is shown below: 4-5 inches around Puget Sound with more towards the Cascades and to the south.

The early afternoon timing is consistent with the NOAA High Resolution Rapid Refresh (HRRR) which snow just getting to Seattle around noon (see below)

Weather.com combines many models and data sources using a sophisticated statistical engine; its forecast is consistent--starting the snow around noon.

Models are very consistent with amount.  The European Center model is suggesting 5-6 inches around Puget Sound by 4 PM Sunday:

Why am I so confident going for this snow event?  Because the models and virtually all the ensembles (running the models many times, each a bit different) are going for this snow event.  For example, here is the European Center ensemble of 51 members for accumulated snow at Seattle (top panel).  Amazing--the prediction are almost all on the same page. Snow starts in the afternoon (09/00 is 4 PM Friday) and all get to the blue colors (2-8 inches).

The bottom line is that the snow will move in during the early afternoon, and there will be some accumulation  (at least an inch) by the drive-time home. By mid-day Saturday many folks will have 5-6 inches around Puget Sound.  Similar amounts will fall over the eastern slopes of the Cascades, with more (like a foot) over the northern side of the Olympics and on the western slopes of the Oregon Cascades.

Now the difficult part.  Can we use this predictive information to avoid disaster tomorrow?  Can we prevent widespread accidents and grid lock?  

I believe we can.     If you can, work from home tomorrow.  Use light rail if you are in Seattle.  If you drive to work or school, head home early (before noon).  And if you drive, park in a location that you will avoid hills.   

Local transportation agencies (SDOT, WSDOT) need to prepare the roads before the snow hits.  That means using lots of salt and other pretreatments BEFORE the snow starts in order to prevent the snow from bonding to the road surface.  And then aggressively plow the snow off, followed by more salt afterwards.