Snow Showers Move Into Western Washington

A band of snow showers has moved into western Washington this morning, but most roads  should be ok.

The 6 AM composite radar image shows the shower activity, which is associated with the approach of an upper level low.  The main band is moving through now and should be out of the way by 8 AM.  But more random snow showers are behind it.

You can also see it in the infrared satellite picture.  Most of the shower activity should be over by 10 AM.

The key issue is temperature, which is marginal since there is onshore flow--coming off the relatively mild Pacific Ocean.   The latest temperature profile from Seattle SnowWatch indicates a freezing level (elevation at which temperatures decline to freezing) at around 1200 ft (see plot), which means the snow level is roughly 200 ft.  So snow is falling nearly to sea level, and even there, wet flakes could mix in during heavier showers.  More snow on top of local hills and away from the water.

Last night's high-resolution UW WRF model run suggested a total snowfall amount through 1 PM of roughly 1-2 inches away from the water....but that is not snow accumulation on the ground....which would be much less (since the snow will be wet, there is melting on the ground, compaction).

A key datum is the road temperature.   Again using the Seattle SnowWatch site one sees the road temperatures (boxes) are above freezing.  Surface air temperatures are are also shown.

So there will be a few hours of snow showers, which may accumulate a bit on grass and bushes above a few hundred feet.  Roads may get a light accumulation during heavy showers that will melt quickly.  During the day, temperatures should warm and the showers should decline. 

There is further snow potential this evening, particularly in any convergence zone forming over  the north Sound.  Last night's WRF run shows snow total through 4 AM Friday shows as much as 3-4 inches of snowfall, which might end up being half that much as accumulation over vegetated surfaces.

Want to see the difference a few hundred feet make?   Here is the latest WSDOT cams at the Mukilteo ferry terminal and at Paine Field (around 450 ft).  No snow at one, a dusting at the other.

from Cliff Mass Weather and Climate Blog https://cliffmass.blogspot.com/2019/03/snow-showers-move-into-western.html