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Area Forecast Discussion (AFD)

Issued by Seattle/Tacoma, WA (SEW)

                            
000
FXUS66 KSEW 192127
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
226 PM PDT Wed Jun 19 2019

.SYNOPSIS...A relatively deep trough will slide southward over 
Western Washington tonight into Thursday bringing some shower 
activity. Weak high pressure will build in Friday and Saturday. 
Another trough approaches the area late Saturday into Sunday and 
settles over the region into early next week.

&&

.SHORT TERM /TODAY THROUGH FRIDAY/...Next trough digging southward 
southwest of Haida Gwaii this afternoon and will shift southeastward 
over the area late tonight. Starting to see some better signs of a 
convergence zone getting started over Snohomish County and expect 
this to get better organized this evening as it slides southward into 
King County. Also seeing a few showers near the San Juans and expect 
a secondary convergence zone to produce some showers there as well 
as into Skagit County. Overall, shower activity will become more 
widespread through the night across the interior and Cascades. The 
coast will only get spotty showers at best with this system. 

Showers will be dissipating on Thursday and should be confined to 
the Cascades by afternoon. Weak high pressure aloft begins nosing 
into the region on Friday with temperatures returning to something 
that resembles normal for the time of year.   

.LONG TERM /SATURDAY THROUGH TUESDAY/...Dry conditions will continue 
for the majority of Saturday but upper ridging flattens quickly 
as next upper trough shifts southward along the British Columbia 
coast. The 12Z runs of the GFS and Euro are in remarkably good 
agreement 
with the path of the upper low through the middle of next week. 
By later Tuesday, the trough looks to be parked just offshore of the 
OR/WA border and doesn't move much as a series of disturbances 
rotate into the region producing periods of showery weather and 
keeping temperatures below normal much of the time.   27

&&

.AVIATION...An upper trough drop down from the northwest through
the area tonight. An upper low will remain inland on Thursday.
West to northwest flow aloft will become northerly later tonight
and Thursday. At the surface, onshore flow will continue with 
high pressure offshore and lower pressure inland. The air mass is 
moist and relatively stable.

5000-8000 foot ceilings this afternoon and evening will lower
1000-2000 feet later tonight. A Puget Sound Convergence Zone is
also possible tonight over central Puget Sound. This could drop 
ceilings locally below 1000 feet. 

KSEA...Mid level clouds will lower tonight. A Puget Sound 
Convergence Zone will probably form just north of the terminal 
this evening, last into the early morning hours Thursday, then
fall apart. Southerly wind 5 to 10 knots could turn northerly for
a few hours this evening, then switch back to southerly later 
tonight. Schneider

&&

.MARINE...Onshore flow will continue through early next week with
high pressure offshore and lower pressure inland. Small craft 
advisory strength west winds are likely most days in the Strait. 
Gales are expected in the Strait tonight and are possible again 
Saturday night. For the Coastal Waters, there will be small craft
advisory strength northwest winds at times through at least Thursday.
There will also be small craft advisory level steep west swell 
through Thursday. Schneider

&&

.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 until 5 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-
     Coastal Waters From Point Grenville To Cape Shoalwater 10 
     To 60 Nm.

     Small Craft Advisory until 11 PM PDT Thursday for Coastal Waters 
     From Cape Flattery To James Island Out 10 Nm-Coastal Waters 
     From James Island To Point Grenville Out 10 Nm-Coastal 
     Waters From Point Grenville To Cape Shoalwater Out 10 Nm.

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

     Gale Warning from 6 PM this evening to 5 AM PDT Thursday for 
     Central U.S. Waters Strait Of Juan De Fuca-East Entrance 
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 6 PM this evening to 8 AM PDT Thursday 
     for Northern Inland Waters Including The San Juan Islands.

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

     Small Craft Advisory until 8 AM PDT Thursday for Admiralty Inlet.

     Small Craft Advisory from 6 PM this evening to 2 AM PDT Thursday 
     for Puget Sound and Hood Canal.

&&

$$

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