Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 192116
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
230 PM PDT SUN JUN 19 2016

.SYNOPSIS...A weak upper level low just offshore will bring a
chance of showers back into the area by Monday evening. Weak high
pressure will build over the region Tuesday. A more significant
trough will move through the area Thursday and Thursday night.

&&

.SHORT TERM...The weak upper level low just offshore looks like it
may spin up a little again and come ashore--for a chance of showers
probably around Monday evening. This little upper low could move
ashore earlier like the UW model--but the WRFGFS doesn`t show much
in the way of shower activity so we may just see some clouds and
only a spotty shower or two. There isn`t much cool air aloft left
with this low, but it may destabilize enough for scattered afternoon
towering CU and a few CBs Monday afternoon. Tuesday will be dry.
The next front out ahead of the next big upper trough has been quicker
in the models--the coast may see a little light rain Wed or Wed night.

.LONG TERM...The next significant upper trough is likely to arrive
Thursday or Thursday night for a good chance of showers. People
heading into the mountains will probably get wet, and maybe a PSCZ
will set up for awhile. After that, the models are looking dry for
the weekend--although there has been a lot of flopping around. This
is a fairly active and troughy pattern, but for the moment the GEM,
GFS, and ECMWF agree that an upper trough arrives around Thursday
and that next weekend will be dry.

&&

.AVIATION...
A weak upper low will spin around over the Washington coastal
waters through Monday giving southerly flow aloft to the area. At
the surface, high pressure over the area will shift north this
evening as a thermally induced trough of low pressure extends
northward into the western Oregon interior, giving northerly low
level flow to the area. The air mass is dry and somewhat stable.

Light shower activity has shifted over Vancouver island and the
offshore waters, while skies across most of the region have cleared.
Partly cloudy skies with good VFR conditions are expected across the
region this evening through early Monday. Albrecht/13

KSEA...Northerly winds 6-12 kt at the terminal this evening. Winds
will slow a bit overnight to 4-7 kt after 06Z. Expect mainly clear
conditions this evening through early Monday.

&&

.MARINE...
Weak high pressure will shift north today, while a thermally induced
trough of low pressure expands northward into the western Oregon
interior valleys this evening through Monday morning. The developing
surface pattern will result in increasing northerly winds across the
region this evening. A small craft advisory remains in effect for
the southern two thirds of the Washington coastal waters starting at
6 PM PDT this evening and continuing through 2 AM PDT Monday.

The thermal trough will shift inland Monday while high pressure
develops over the offshore waters. This will result in the
development of moderate to strong onshore flow late Monday
afternoon and Monday night. A gale watch has been issued for the
possibility of gale force winds Monday night in the central and
eastern portions of the Strait of Juan De Fuca. Small craft
advisory conditions appear likely Monday night in Admiralty Inlet
and portions of the Northern Inland waters Monday evening as the
inflow through the strait increases.

Onshore flow will gradually weaken Tuesday and Tuesday night. Then
varying degrees of onshore flow are expected Wednesday through the
end of the week. Albrecht/13

&&

.SEW Watches/Warnings/Advisories...
WA...None.
PZ...Small Craft Advisory from 6 PM this evening to 2 AM PDT Monday
     for 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.

     Gale Watch from Monday afternoon through Tuesday morning for
     Central U.S. Waters Strait Of Juan De Fuca-East Entrance
     U.S. Waters Strait Of Juan De Fuca.

&&

$$

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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