Dangerous Icing and Super Inversion over Western WA This Morning

Roadway conditions are quite dangerous over much of western Washington, particularly on less traveled roads, as the combination of freezing fog and frost has put a glaze on many roadway surfaces (and pathways).

Foggy Sunrise Over Seattle

With high pressure in place, skies are relatively clear aloft allowing good radiational cooling to space from the surface.  At the same time, temperatures aloft have warmed.  The result is a super inversion, with temperature increasing rapidly with height.  Here are the latest temperatures above Seattle from the radar-wind profiler at Sand Point.  An increase of 12C (22F!) in 800 meters (2600 ft)

 Here are the 7 AM observations around the region.  Lots of fog and air temperature at and below freezing at many locations.  And remember these temperatures are taken at 2 meters above the surface--the surface is colder!

Really dangerous, so be careful.   The street in front of my house is all glazed up...I will have to be extremely careful in my bike in to work.  Fog is more extensive this AM because the offshore flow has weakened, something shown by the time-height cross section for the observations above Seattle-Tacoma Airport (red temps, blue winds, height in pressure...850 being about 5000 ft, time increasing to the left).

Why is fog and subfreezing temperatures so dangerous?  Because fog has a lot of water content and can freeze rapidly on roadway surfaces.  So, an image like this spells DANGER on a cold morning.

And in this one, you can SEE the ice on the roadway!

Some folks have reported strange sound effects with the strong temperature inversion, hearing boat horns many miles away.