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Area Forecast Discussion (AFD)

Issued by Seattle/Tacoma, WA (SEW)

FXUS66 KSEW 160952

Area Forecast Discussion
National Weather Service Seattle WA
300 AM PDT Thu Aug 16 2018

.SYNOPSIS...Onshore flow has brought marine layer clouds into 
parts of Western Washington this morning. Air quality has improved. 
Clean marine air will push inland from the coast again tonight.
Light offshore flow is likely for a couple of days early next week.


.SHORT TERM...Areas of night and morning low clouds will push from 
the coast into parts of the interior for the next few days. Temps 
will bottom out a little on the cool side Friday, but should rebound 
a notch Saturday. There is scattered convection over northeast 
Oregon and the Columbia Basin early this morning--but that will miss 
our area entirely. The main weather story is the improvement in air 
quality as clean marine air pushed into the area--and another push 
of marine air will occur tonight. There will be some smoke aloft at 
times, but the low levels should be in good shape for several days.

.LONG TERM...High pressure will be offshore with lower pressure over
the Pacific Northwest. A couple of hazy smoky days are not a bad bet
and another marine push is likely around the middle of next week.


.AVIATION...Flow aloft will remain southwesterly today as a 
weak upper level trough works onshore. Strengthening onshore flow 
has brought marine stratus into the south interior and south Puget 
Sound as well as the Strait of Juan de Fuca as of 09 UTC. Expect 
stratus to fill in much of the interior lowlands by by daybreak with 
IFR conditions lingering into mid morning before lifting and 
scattering out around midday for most areas. Lingering smoke 
affecting the area will remain aloft, and not impact the surface.

KSEA...Marine stratus is expected to reach the terminal by 12 UTC 
with IFR ceilings and MVFR visibilities. Low clouds/fog will 
dissipate by 1800 UTC. Winds will remain south/southwest 10 mph or 


A 1030 mb high well offshore with lower pressure east of the 
Cascades will keep the flow onshore or westerly flow through 
Saturday. The flow will strengthen late this afternoon for the 
possibility of gale force winds over parts of the Strait of Juan 
de Fuca. 


PZ...Gale Watch from this evening through late tonight for Central 
     U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. 
     Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 5 PM this afternoon to midnight PDT 
     tonight for West Entrance U.S. Waters Strait Of Juan De 

     Small Craft Advisory until 6 PM PDT this evening for Central 
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 6 AM PDT Friday for Coastal Waters 
     From Cape Flattery To James Island 10 To 60 Nm-Coastal 
     Waters From James Island To Point Grenville 10 To 60 Nm.