Smoke Starts to Recede as Marine Air Pushes into Western Washington

A weak inland push of marine air occurred this morning, resulting in dramatic improvements of air quality along the coast, in the Strait of Juan de Fuca and over the south Sound.   On the other hand, some locations over NE Washington have worsened smoke, as local fires have added to the plumes from British Columbia.  Seattle, located in the dead zone behind the Olympics, has not enjoyed much improvement yet...but the smoke will slowly lessen during the next day.

The NASA MODIS satellite imagery shows low clouds along the coast, with some tendrils moving inland through the coastal mountains.   Western Oregon and SW Washington are less smoky, but some smoke is still evident over Puget Sound.  Dense smoke is found over NE WA from a combination of the smoke from BC and local fires (e.g., the Diamond Creek fire).  Very bad over Bellingham and Vancouver.

 Compare today's MODIS image to yesterday's at the same time (around 1 PM).
More smoke over the offshore waters and SW Washington.  Better over NE WA.

Air quality has improved at several locations, but gotten worse at others. Here is the data, showing  a plot of the concentration of small particles (PM2.5).  Seattle (blue) is slightly better, but Aberdeen, Mount Vernon, and Cheeka Peak (NW tip of the Olympics) are almost back to normal.  In contrast, Twisp--in the eastern foothills of the North Cascades--is a disaster, with a huge spike in particles.

A solar radiation measuring device near Twisp indicated a LOSS of 70% of the normal radiation from the sun.  Unbelievable.

Improvement in western Washington is occurring as the thermal trough jumped into eastern WA and an onshore pressure gradient has developed, in turn forcing onshore winds.  You can see this trend from the winds above Seattle (see time0/eight cross section below, time on x axis, height in y).  Both winds (barbs) and temperature--red lines--are shown.  The strong northerly winds of the past few days are gone (which blew in the smoke), but the winds are too light to really mix out our smoky surface layer.

The forecasts model for tomorrow show a continuation of weak onshore flow...this will bring down temperatures (into the upper 80s, but still way above normal), but not enough to clean out the lower atmosphere of western WA.

We are simply not going to cool down much over the weekend.  The reason...an amazingly persistent ridge of high pressure over the West Coast (see map for Saturday afternoon at 500 hPa).  And folks, there is little doubt we are going to break the big record for consecutive dry days (51).

from Cliff Mass Weather and Climate Blog http://ift.tt/2wtJi0H