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Area Forecast Discussion (AFD)

Issued by Seattle/Tacoma, WA (SEW)

                            
000
FXUS66 KSEW 231851
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
1151 AM PDT Sun Jun 23 2019

.UPDATE...Updated MARINE section for stronger winds through the
Strait of Juan de Fuca.

&&

.SYNOPSIS...Onshore flow will continue. An upper trough will move 
over the Pacific Northwest by the middle of the week with showers 
increasing. The trough will move out of the area late in the week. 

&&

.SHORT TERM /TODAY THROUGH TUESDAY/...Mostly cloudy skies, a 
few areas of morning drizzle, and scattered showers will be the rule 
through today through Monday. Satellite imagery this morning shows 
that parts of the Olympics have sunshine and there is a patch of 
clearing off the north coast--a few more areas ought to open up and 
have some afternoon sun today and Monday, the south part of Western 
WA and around the San Juans and Strait of Juan de Fuca. The PSCZ 
area and west slopes of the Cascades will probably only see some 
afternoon and evening sunbreaks and then will fill in again quickly 
overnight. It will remain cool. Tuesday will probably be a little 
warmer and brighter--with less low level moisture in lighter onshore 
flow. An approaching upper trough will increase the chance of 
showers Tuesday afternoon or evening as the flow aloft becomes 
southerly and the air destabilizes.

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...Extended models still in
good agreement with the upper level trough moving over Western 
Washington on Wednesday and remaining over the area Thursday 
keeping showers in the forecast both days. Trough kicking out to 
the northeast on Friday with a weaker trough moving through the 
area early Saturday followed by some weak upper level ridging 
developing offshore. Friday looks to be the transition day with 
showers still in the forecast but shower chances decreasing before
the forecast dries out on Saturday. High temperatures remaining a
little below normal Wednesday through Friday, mostly in the upper
50s to mid 60s. Some warming on Saturday getting highs back to to
near normal, lower 60s to lower 70s. Felton

&&

.AVIATION...Generally widespread MVFR conditions with isolated 
IFR and drizzle this morning with the exception of the northern 
Olympic Peninsula (including KCLM). Most areas will once again 
struggle to break up today, with most areas seeing CIGS top out 
BKN between 3000-4500 feet later this afternoon. CIGS will drop 
again this evening, reaching low-end MVFR to high-end IFR 
overnight. Another window for a potential convergence will develop
this afternoon across King/Snohomish County, potentially bringing
some north winds through the central Puget Sound as far south as 
KSEA. Outside of that, winds will generally be west to southwest 
6-12kt with some isolated higher gusts possible at KBLI, KCLM, and
KHQM.

KSEA...MVFR CIGS generally expected to rise today, likely reaching
around BKN040 late this afternoon/early evening before falling
back down to low-end MVFR overnight. Winds generally 6-12kt
through the period. Drizzle will taper off mid-morning but 
another convergence zone will bring back precipitation chances 
this evening and overnight. This convergence zone has the
potential to result in a period of north winds at the airport 
this evening (most likely between 01z- 07z). -Wolcott-

&&

.MARINE...Onshore flow continues today, stronger than forecast
through the central/eastern Strait of JDF. Upgraded SCA to Gale
Warning through 06z then SCA through 15z for that area. SCA for
the adjacent waters was left in place.

Guidance continues to suggest that gradients will relax during 
the first half of the upcoming week, though periods of 
precipitation are expected as a slow moving upper level low 
settles over/near the area. Daily westerly pushes through the
Strait of JDF are likely. -Wolcott-

&&

.HYDROLOGY...The daily hydrology discussion has ended until the
start of the next rainy season; it will only be updated as needed
until then.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 11 PM this evening to 8 AM PDT Monday 
     for Central U.S. Waters Strait Of Juan De Fuca-East 
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Gale Warning until 11 PM PDT this evening for Central U.S. 
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters 
     Strait Of Juan De Fuca.

     Small Craft Advisory until 5 AM PDT Monday for Admiralty Inlet-
     Northern Inland Waters Including The San Juan Islands.

&&

$$

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