Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 210340
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
845 PM PDT MON JUN 20 2016

.SYNOPSIS....A weak upper low just offshore will move through the
area tonight for a chance of showers. Weak high pressure will
build over the region Tuesday. Another upper level low will move
through the area Thursday night bringing showers Thursday and
Friday. A weak upper level ridge will build over Western
Washington for warmer and drier weather this weekend into early
next week.

&&

.SHORT TERM...The evening has been characterized mainly by clearing
skies, though there is still accas present and there has been a
persistent thunderstorm over the north Olympic peninsula. Another
thunderstorm in south Pierce county is moving north; it will
probably remain in or near the Cascades. The grids and forecasts
have already been updated.

Clouds are likely to increase over most areas late tonight as an
upper low moves east and onshore surface gradients rise. Showers on
Tuesday should be confined to the Cascades and there will be
afternoon clearing. Highs Tuesday will be in the mid 60s to mid 70s.

On Wednesday and Wednesday night a weak surface front will stall off
the coast and then move inland bringing a chance of precipitation
mainly to the coast and Olympics. Highs Wednesday will be similar to
Tuesday`s.

Another upper level low will approach the coast Thursday and move
inland Thursday night. This will bring chance pops to the region
Thursday morning and likely pops in the afternoon and evening. Highs
on Thursday will be several degrees lower. Burke

.LONG TERM...Previous discussion...Models are indicating residual
showers, especially in the mountains, on Friday from the upper level
low moving out of the area. The GFS, ECMWF, and GEM models are all
showing an improving trend for the weekend and early next week with
a ridge building in and drier and warmer weather in store. Smith

&&

.AVIATION...Southwest flow aloft over Western Washington this
evening will veer to westerly tonight, as the upper low just
off the coast moves inland and a weak upper ridge moves into the
offshore waters. The air mass is somewhat moist and unstable, with
isolated thunderstorms over the mountains, but it will stabilize
in the next few hours. The mid and upper levels will dry, but a
moist low level marine layer will push inland tonight in
increasing onshore flow.

MVFR conditions should become widespread late tonight 10Z-13Z with
bases of marine stratocumulus probably around 012-016 in most
areas. The morning clouds will burn off late morning through
afternoon for VFR conditions with ceilings generally above 120.

KSEA...South to southwest wind 7-13 kt gusting 20 kt, probably
shifting to northwest 5-10 kt late Tuesday afternoon. Marine
stratus should push inland to KSEA tonight, giving BKN-OVC013beginning
around 10Z. McDonnal

&&

.MARINE...Onshore flow developed late today and will increase
through this evening with small craft advisory winds over the
outer coastal waters, the central and eastern Strait of Juan de
Fuca, and adjacent parts of Admiralty Inlet and the northern
inland waters.

Weaker onshore flow will continue Tuesday and Tuesday night. A weak
front will move through the coastal waters Wednesday, but onshore
flow will prevail through the end of the week. McDonnal

&&

.SEW Watches/Warnings/Advisories...
WA...None.
PZ...Small Craft Advisory until 5 AM PDT Tuesday 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-Northern Inland Waters Including The San Juan
     Islands.

     Small Craft Advisory until 9 AM PDT Tuesday for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.

     Small Craft Advisory until midnight PDT tonight for Admiralty
     Inlet.

&&

$$

www.weather.gov/seattle

You can see an illustrated version of this discussion at
www.weather.gov/seattle/gafd/latest_webafd.html



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