Small Craft Advisory 134, NWS Seattle, WA

Area Forecast Discussion
National Weather Service Seattle WA
930 PM PDT SUN JUN 5 2016

.SYNOPSIS...Temperatures will moderate over the next few days as an
upper ridge moves slowly east. Onshore surface flow will develop
tonight and Monday, and low clouds will spread further inland each
night through Tuesday night. An upper level trough will bring much
cooler conditions, clouds, and a chance of showers to the area later
this week.

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.SHORT TERM...The way records have been broken today...one would
think that W WA had a problem with vinyl. Climate sites that broke
records today include Sea-Tac with 93...Olympia with 97...Bellingham
with 85 and here at the NWS office with 91. For other interesting
stats of this nature...check out AWIPS PIL SEARERSEW.

While the thermal pressure trough responsible for this has pushed
east...and good riddance...the upper level ridge will remain in
place. This means that while onshore flow will be present to cool
things somewhat...high temperatures tomorrow still look to be in mid
80s for interior lowland locations. While this is indeed a relief
compared to high temps today...it is still 10-15 degrees above what
is normally expected this time of year. As the ridge slowly plods
eastward Monday and Tuesday...can expect marine are to nudge inland
just as slowly.

Models remain consistent that an upper level trough will start to
impact the area Wednesday bringing increased clouds and dropping
temperatures to near normal. Precip is also a possibility...but best
chances for that look to hold of Wednesday night into Thursday.

Inherited forecast looks good. No changes or updates needed this
evening.  SMR

.LONG TERM...From 315 PM discussion...The upper low will affect
weather into the weekend. Heights remain low, plunging into the 550s
when the low or trough finally moves through the region. Yesterday
models showed that happening on Friday but today they show it on
Saturday. Showers are likely on whatever day that is, and there is
at least a chance of showers every other day. For now have kept the
forecast as a broad brush mostly cloudy with a chance of showers.
High temperatures will be mostly in the 60s Thursday through Sunday.
Burke

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.AVIATION...A large upper level ridge over the western U.S. will
maintain a warm dry air mass over W WA through Monday. Light SW flow
aloft will prevail with the ridge axis over W MT. A surface ridge
just offshore combined with a thermal surface trough over E WA will
allow onshore flow to develop tonight. The onshore flow will allow
low stratus clouds to develop along the coast from 06z-19z with the
clouds spreading partway inland through the strait of Juan de Fuca
and inland to maybe around Shelton (KSHN), but not reaching the
interior around Puget Sound. Otherwise, skies will remain mostly
clear.

KSEA...mostly clear skies with just some high clouds at times.
Surface winds will remain north 5-10 kt through 08z. Developing
onshore flow should shift the surface winds to SW 5 kt around 12z,
then to W 3-7 kt 16z-20z. Kam

&&

.MARINE...A surface trough has shifted over E WA this evening
while a surface ridge continues over the WA offshore waters.
Moderate onshore is developing this evening and west winds are
rising in the strait of Juan de Fuca, where a small craft advisory
is in effect for the central and east strait. SCA's are also in
effect for the inland waters adjacent to the strait, notably the
southern San Juan Islands and Admiralty inlet, as well as the WA
coastal waters.

The forecast for the strait continues to be a little uncertain,
mainly because it is so easy for a gale to occur at Race Rocks. The
UIL-BLI pressure gradient has risen to 2.2 mb at 03z, which is on
target with respect to the GFS which has a peak gradient of 3.2 mb
at 09z tonight. This is borderline territory for a Race Rocks gale
but not really anywhere else. Other recent model guidance keeps the
winds just below gale, so I will stick with a 20-30 kt SCA for the
strait for now.

Models have remained consistent in showing stronger onshore flow
developing Monday evening. The GFS shows 4.2 mb through the strait
at 03z. A gale watch remains in effect but confidence is higher that
gales will develop Monday evening. The offshore surface ridge will
remain in place through this week but onshore flow should be weaker.
Kam

&&

.SEW Watches/Warnings/Advisories...
WA...None.
PZ...Small craft advisory coast, central and east strait of Juan
      de Fuca, Admiralty inlet, north inland waters.

     Gale watch Monday afternoon through Monday evening for the
      central and east strait.

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www.weather.gov/seattle

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