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Area Forecast Discussion (AFD)

Issued by Seattle/Tacoma, WA (SEW)

FXUS66 KSEW 131739 AAA

Area Forecast Discussion
National Weather Service Seattle WA 
936 AM PST Tue Nov 13 2018

.SYNOPSIS...Weather over Western Washington will transition today as 
high pressure aloft weakens while a warm front reaches the coast 
this afternoon with rain spreading inland afterward. A secondary 
system will keep conditions wet Thursday and into Friday. Upper 
level ridging is expected to resume over the weekend allowing for 
dry conditions as well as overnight and morning fog. A front may 
approach the region early next week with a chance of rain.


.SHORT TERM...A combination of current satellite imagery and a peek 
out the window shows some high clouds over W WA this morning...and 
will likely see cloud cover increase steadily throughout the day as 
high pressure aloft exits the area allowing for the next weather 
system...an approaching warm front...to bring rain into the area. 
This feature is expected to reach the coast this afternoon with rain 
then spreading inland tonight while keeping rain in the forecast for 
into Wednesday.

Models suggests a brief break in the action Wednesday night and into 
Thursday morning before a secondary system Thursday afternoon and 
evening...tapering off by midday Friday. As one would 
expect...models having their usual discrepancy...the ECMWF bringing 
in the system earlier and with more widespread precip...the GFS 
being later and with less precip. Get a new shtick fellas. Models 
fall back into agreement with another upper level ridge building 
over the Pacific allowing dry conditions to return Friday.

Inherited forecast covers the above well...see no reason for morning 
updates at this time.  SMR

.LONG TERM...From Previous Discussion...Global models agree on 
building a strong ridge over the region Friday through the weekend. 
The air mass will gradually dry, but moisture will become trapped 
near the surface, beneath the subsidence inversion. Expect chilly 
nights with areas of fog and freezing fog. Cold pockets will dip to 
the upper 20s and the milder metro areas will be in the 30s, with 
frost likely. 

Long range models have also trended toward a stronger ridge
solution that could keep the area dry out through Monday. Timing
of the next front is uncertain, and did not make much change to
end of the forecast period. There is a chance rain could return
late Monday or Tuesday, or be delayed due to the strong ridge.



.AVIATION...Broken high clouds present across the area this
morning with VFR conditions. A weak front will move inland on the 
coast this afternoon and across the rest of the area later this 
evening into Wednesday. Light rain is expected across the area as 
this system moves through. Conditions will likely bounce around from 
VFR to MVFR during this period. Aloft, southwesterly flow today will 
shift to the west tonight into Wednesday. Southerly winds at the 

KSEA...Above discussion applies. VFR conditions today into this 
evening with broken high cloud deck. Showers will move in after 3-4Z 
this evening, continuing through about 18-20z Wednesday. Cigs/vsby 
may jump around from VFR to MVFR Wednesday morning. Winds will be 
southerly to 10 kts through the period. CEO


.MARINE...A weak front will approach the area this afternoon and
move inland tonight into Wednesday. Small craft advisory conditions 
expected across most of the coastal, Strait, and inland waters with 
the exception of the central Strait. A brief period of onshore flow 
likely in its wake with winds relaxing slightly during the day 
Wednesday. A second weak system will then clip the area on Thursday. 
Offshore flow will return this weekend.


.HYDROLOGY...A frontal system will bring rain at times to most of 
Western Washington later this afternoon through late Wednesday. The 
initial warm front will produce moderately strong southwest flow 
aloft which will enhance rain amounts in the mountains. Meso models 
indicate 1-2 inches at most over roughly a 36 hour period. This 
amounts to a nice rain, but not much more than that. Area rivers 
will see a bit of a bump up from the storms. Bottom line is that 
flooding is not expected on area rivers through the next 7 days. 


PZ...Small Craft Advisory until 2 AM PST Wednesday for Coastal Waters 
     From Cape Flattery To James Island 10 To 60 Nm-Coastal 
     Waters From Cape Flattery To James Island Out 10 Nm-Coastal 
     Waters From James Island To Point Grenville 10 To 60 Nm-
     Coastal Waters From James Island To Point Grenville Out 10 
     Nm-Coastal Waters From Point Grenville To Cape Shoalwater 
     10 To 60 Nm-Coastal Waters From Point Grenville To Cape 
     Shoalwater Out 10 Nm-West Entrance U.S. Waters Strait Of 
     Juan De Fuca.

     Small Craft Advisory until 10 AM PST Wednesday for Admiralty 
     Inlet-East Entrance U.S. Waters Strait Of Juan De Fuca-
     Puget Sound and Hood Canal.

     Small Craft Advisory from 4 PM this afternoon to 10 AM PST 
     Wednesday for Northern Inland Waters Including The San Juan