FXUS66 KSEW 132231
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
331 PM PDT Thu May 13 2021

.SYNOPSIS...Dry westerly to northwesterly flow aloft will persist 
through Friday. Upper level ridging will build over the region 
this weekend with sunny skies and warmer temperatures through 
Sunday. The ridge is expected to weaken Monday setting up a more 
active weather pattern with a series of weather systems moving 
into the area next week.

&&

.SHORT TERM /TONIGHT THROUGH SUNDAY/...Most of the mid- and high-
level clouds embedded in the northwesterly have been limited to 
the south of Puget Sound this afternoon with sunny skies and 
temperatures in the upper 60s and low 70s. A weak upper level 
trough will move south of the area Friday which will do little 
more than nudge the flow aloft to the northwest with any increase 
in mid and upper level clouds well to the south over Oregon. 
Northwesterly surface gradients overnight will result in stratus 
along the coast and parts of the Strait and Admiralty Inlet by 
Friday morning. Fewer clouds Friday will give high temperatures a 
bit of a head start over the interior reaching into the mid 70s 
over the interior and near 60 degrees along the coast. 

An upper level ridge will build into Western Washington Friday 
night and Saturday with northwesterly low level flow keeping night
and morning stratus pinned to the coast. Sunny morning skies over
the interior will boost temps over the interior into the mid 
70s, and lower 60s along the coast. 

.LONG TERM /MONDAY THROUGH THURSDAY/...Ensembles continue to
support the notion of the ridge remaining in place Sunday, making
the warmest day in the forecast period with the warmest locations
getting into the upper 70s. A weak marine push Sunday night into 
Monday morning will cool temperatures over the interior with the
weakening ridge - supported by the ensembles - showing an 
increasing potential for showers mainly Monday evening. Tuesday 
and Wednesday continue to look more unsettled with a cool upper 
level trough over the area. Lower snow levels Monday night onward
will dip to near 4500 feet Tuesday and as low as 3500 feet 
Wednesday. Much cooler high temperatures Tuesday and Wednesday 
will reach only into the mid 50s to around 60. 

&&

.AVIATION...Pattern defined by northwesterly flow aloft, while
high pressure at the surface continues to promote onshore flow in
the low levels. Satellite this afternoon shows generally clear
skies across the interior of Western Washington, as stratus has
retreated back to the Pacific Coast. This has allowed for conditions
at area terminals to rebound back to VFR this afternoon, with 
just some cirrus around 25kft and some scattered cumulus passing
overhead through the afternoon and evening hours. Another round of  
stratus looks to push inland overnight, however guidance hints it
will be less widespread than this morning. Any areas in stratus
will likely see a few hours of MVFR to IFR conditions on Friday, 
before stratus retreats back to the coast by 17-18Z. Northerly 
surface winds will ease and become light this evening, before 
increasing back to 5-10kts Friday morning. 

KSEA...VFR conditions through this evening with passing cirrus
overhead. A brief period of stratus could make it into the
terminal Friday morning and could briefly reduce visibilities to
MVFR. N winds will become light this evening, increasing slightly to
5-10kts Friday morning. 14

&&

.MARINE...High pressure offshore will remain the dominant
influence in the low levels over the next couple of days. This 
will help to keep Western Washington in an onshore flow regime, 
and will likely yield additional mornings with low stratus and 
areas of fog over portions of the area waters (especially the 
coastal waters.)

This evening, a stronger diurnal push is expected down the Strait, 
which will prompt a small craft advisory for the central and eastern 
portions of the area. West wind of around 25kts can be expected 
from mid- evening to shortly before sunrise Friday. NW wind over 
the outer Coastal Waters will also pick up to small craft 
criteria this evening and looks to remain elevated through much of  
the weekend.

Otherwise, expect additional diurnal westerly pushes down the 
Strait each evening and overnight period into early next week.
Guidance still indicates that the pushes will strengthen each 
day, with gradients still indicating the possibility for gale 
force winds in the Strait Sunday evening/night. 

Seas and swells appear rather calm over the next week at generally 
7ft or less. 14

&&

.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 7 PM this evening to 5 AM PDT Friday 
     for Central U.S. Waters Strait Of Juan De Fuca-East 
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 7 PM this evening to 1 AM PDT Saturday 
     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-Coastal Waters From Point Grenville To Cape 
     Shoalwater 10 To 60 Nm.

&&

$$

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