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Area Forecast Discussion (AFD)

Issued by Seattle/Tacoma, WA (SEW)

FXUS66 KSEW 251629

Area Forecast Discussion
National Weather Service Seattle WA
930 AM PDT Fri May 25 2018

.SYNOPSIS...Today will be dry and any clouds should dissipate. 
Onshore surface flow will increase tonight, bringing marine clouds 
inland along with areas of drizzle Saturday. The pattern will remain 
similar through Memorial Day. Next week will be a little cooler.


.SHORT TERM...There are clouds over most of the interior this 
morning, but the coast, Olympics, and northwest interior are mostly 
clear. Most of the cloudiness will evaporate this afternoon and 
especially this evening. Little if any drizzle will fall out of the 
clouds today. Highs today will be 65-70 over the interior, with 
lower 60s on the coast. 

Onshore flow will increase tonight. Westerly gales are likely in the 
strait tonight, and marine stratus will arrive over the interior 
late tonight. The marine layer is likely to be thick enough to 
produce areas of drizzle. High temperatures will again be in the 60s.

Onshore surface flow will weaken considerably Saturday night and 
Sunday. This will mean fewer clouds and no drizzle on Sunday. With 
plenty of sunshine, temperatures will be higher, with mid 60s on the 
coast and low to mid 70s inland. Burke

.LONG TERM...Previous discussion...Memorial Day is still expected to 
be dry, and temperatures should be about the same or slightly lower 
than on Sunday. So, it still looks like a nice day for outdoor 

The GFS and Canadian models were now close to the ECMWF solution 
in regards to the timing of the midweek system. Thus, the ECMWF 
was the model of preference for this period (Memorial Day thru 
Thursday). Expect onshore flow to strengthen on Memorial Day in 
response to the approaching upper level trof. This trof will move 
the area on Tuesday for cooler and cloudier conditions. The models
were drier with this system; therefore, decided to confine the 
mention of showers to the Puget Sound Convergence Zone and the 
north Cascades. 

The Pacific Northwest will remain under the influence of low 
pressure aloft Wednesday through Thursday for below normal temps. 
There will be a chance of showers over mainly the mountains and 
within the Puget Sound Convergence zone.


.AVIATION...The tail end of a weak upper trough will brush by
Western Washington late today. This will strengthen low-level
onshore flow. Current marine clouds over the interior will burn
off around mid-afternoon. Expecting greater coverage of marine
clouds and somewhat lower cigs on Saturday AM. Moderate southwest
flow aloft today will become weak northwesterly on Saturday. The
air mass will be stable, with a moist marine lower down low and
dry air above.

KSEA...Stratus burnoff now expected around 21z. Winds will be
light and variable until 21z, then pick up a bit out of the north.
A turn back to light southerly wind is expected late this evening,
in the 05z-07z time frame. More marine clouds on Saturday morning,
with cigs below 020 expected. Haner


.MARINE...Moderate to strong onshore flow will continue through 
the Memorial Day weekend. This will lead to near gale or gale 
force winds over the central and eastern Strait of Juan de Fuca, 
mainly during the late afternoon through overnight hours through 
this weekend. The strongest onshore flow is expected this evening.
Gale Warnings are in effect for the Central and Eastern Strait
during the normal diurnal peak this evening. Haner


PZ...Small Craft Advisory until midnight PDT tonight for Coastal 
     Waters From Point Grenville To Cape Shoalwater Out 10 Nm.

     Gale Warning until 3 AM PDT Saturday for Central U.S. Waters 
     Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of 
     Juan De Fuca.

     Small Craft Advisory from 2 PM this afternoon to 3 AM PDT 
     Saturday for Admiralty Inlet-Northern Inland Waters 
     Including The San Juan Islands.

     Small Craft Advisory until 9 PM PDT this evening for West 
     Entrance U.S. Waters Strait Of Juan De Fuca.