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Area Forecast Discussion (AFD)

Issued by Seattle/Tacoma, WA (SEW)

                            
000
FXUS66 KSEW 240314
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
815 PM PDT Tue Apr 23 2019

.SYNOPSIS...Onshore flow will decrease overnight and high pressure 
will build toward the area. A weak ridge will keep the weather dry 
Wednesday and Thursday. An upper trough will bring a chance of 
showers and cooler weather to the region by the weekend.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY/...Clouds are mainly in the 
convergence zone this evening and along the west slopes of the 
Cascades. Skies are starting to clear elsewhere. After areas of 
morning clouds--skies should be partly to mostly sunny by midday 
Wednesday. A broad and progressive upper ridge will give low level 
northerly flow to the area as well as drying on Wednesday. Highs 
will be mainly in the upper 50s to mid 60s. 

A broad and weak upper trough will approach the area from the west
on Thursday. A rather thick layer of moisture in the mid and upper
levels will bring increasing clouds to the area through the day,
then some lower clouds will spread inland during the evening hours
as low level flow becomes onshore ahead of the incoming trough.
Despite the cloud cover, expect highs to be in the 60s. Despite 
the increase in moisture aloft, expect it to remain dry.

The broad trough with increasing flow aloft will give partly to
mostly cloudy skies to the region on Friday along with an
increase in onshore flow and a chance to slight chance of showers
(mainly to the Cascades and northern portions of the area).
Onshore flow will result in daytime temperatures falling a few
degrees, back to around the 60 degree mark. 

.LONG TERM /SATURDAY THROUGH TUESDAY/...Troughing will dominate
conditions over the weekend. Models continue to show mainly only
chance pops with partly to mostly cloudy conditions across the
region. Snow levels will be low, as low as 3000 ft or so at times,
so some snow showers may be seen in even the lower passes.
Precipitation amounts appear that they will be rather light, so
no significant impacts are expected at this time. 

Models generally agree that the early week period will be
dominated by a weak trough that will provide partly to mostly
cloudy conditions with a chance of showers and temperatures near
normal for late April. While models do show a good deal of
consistency today, their continuity with previous solutions is
not good. Forecasts represent a blend of the ECMWF with the
National Blend of Models. Albrecht

&&

.AVIATION...Clouds are mainly in the convergence zone area and into 
the Cascades this evening, with clearing skies outside of the zone. 
On Wednesday skies should be mostly sunny after areas of morning 
clouds, with just some scattered fair weather cumulus and maybe a 
little cirrus.

KSEA...There are clouds in the convergence zone and that will 
continue through the night. Skies will scatter out Wednesday, 
perhaps not at 18z but that is the forecast for now.


&&

.MARINE...Strong onshore flow will ease overnight and then winds 
will be more northerly Wednesday. Marine air will push back into the 
area Thursday and then an upper trough will move toward the area 
late in the week--for strengthening onshore flow.


&&

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

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 8 PM this evening to 8 AM PDT 
     Wednesday 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 from 8 PM this evening to 5 AM PDT 
     Wednesday 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.

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

     Small Craft Advisory until 3 AM PDT Wednesday for Northern 
     Inland Waters Including The San Juan Islands.

     Small Craft Advisory until 5 AM PDT Wednesday for Admiralty 
     Inlet.

     Small Craft Advisory from 8 PM this evening to 2 AM PDT 
     Wednesday for Puget Sound and Hood Canal.

&&

$$

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