Small Craft Advisory 128, NWS Seattle, WA

Area Forecast Discussion
National Weather Service Seattle WA
336 AM PDT Mon May 22 2017

.SYNOPSIS...Warmest days of the year for most places today with an
upper level ridge over the area. Strong onshore flow will develop
on Tuesday with an upper level trough rapidly moving toward
Western Washington spreading clouds into the area and bringing
cooler conditions. The upper trough will weaken and shift east
Thursday and an upper ridge will arrive next weekend.

&&

.SHORT TERM...Satellite imagery shows upper level ridge over
Western Washington early this morning with the ridge axis on top
of the area. High clouds streaming through the ridge cover most of
the area at 10z/3 am. Temperatures were in the 50s and lower 60s.

Warmest day of the year in store for most of the area today with
the upper level ridge remaining over Western Washington. 500 mb
heights are in the mid 580 dms with 850 mb temperatures peaking
this afternoon around plus 16c. Surface gradients never really
turn solidly offshore and by 00z Tuesday the gradients are
northwesterly. This will put a cap on the high temperatures with
upper 80s being the warmest temps but even locations near the
Strait will at least get into the mid 70s.

Upper level ridge starts to weaken tonight with an upper level
trough approaching Haida Gwaii. Trough still far enough to the
north and west to not result in any changes in the surface
gradients. Lows will mostly be in the 50s.

Trough rapidly moving toward Western Washington on Tuesday with
the surface gradient going strong onshore. High end gale force
winds are expected in the Strait of Juan de Fuca by the end of the
day. With the marine air flooding inland in the afternoon high
temperatures will be much cooler than Monday with highs on the
coast staying in the 50s with mid 60s to mid 70s common over the
interior.

Upper level trough moving over Western Washington Tuesday night
and remaining over the area on Wednesday. Nothing really organized
with the trough but with the change of air mass and some
instability a chance of showers can not be ruled out. High
temperatures over the interior will continue to cool with highs
only in the 60s with highs near 60 along the coast. Lows Tuesday
night will be in the mid 40s to mid 50s.

.LONG TERM...Extended models in pretty good agreement this morning
with the upper level trough over the area on Thursday and the
trough moving east Friday. Upper level ridge offshore building
into Western Washington for the holiday weekend. Chance of showers
on Thursday with the shower chances confined to the Cascades on
Friday. Have taken the chance of showers out of the forecast for
Cascades on Saturday. Extended models are trending toward a
stronger ridge Friday through the holiday weekend. If the trend
continues look for the chance of showers to get taken out of the
forecast for the lowlands on Thursday. High temperatures will
slowly warm through the period from 60s and lower 70s on Thursday
to upper 60s to near 80 by Sunday. Felton

&&

.AVIATION...The upper level ridge over the region will continue to
build today before heights begin to fall this evening ahead of
system approaching the area from the northwest. Flow aloft will
remain light and northerly. At low levels high pressure over the
offshore waters will drive onshore flow today with light northerlies
through the interior. The air mass will remain dry and stable today
with VFR conditions.

KSEA...VFR conditions with northeasterly winds 6 to 8 knots
this morning becoming northwesterly 8 to 12 kt around midday.

&&

.MARINE...High pressure over the offshore waters will keep
northwesterly onshore flow going through tonight. Strongest flow is
expected again during the evening hours over the coastal waters,
then through the central and east Strait after midnight. Onshore
gradients will further increase Tuesday as a disturbance over the
Gulf of Alaska approaches from the northwest. Gradients peak Tuesday
afternoon highlighting a very strong marine push during the late
afternoon and overnight hours on Tuesday. A gale watch has been
issued to highlight the potential for strong gale conditions for the
central and eastern Strait of Juan de Fuca, as well as for marginal
gale conditions in Admiralty Inlet and in portions of the Northern
Inland Waters. Small Craft Advisory conditions are possible for the
the remaining waters. A steep fresh swell will develop off Vancouver
Island and push into the coastal waters later Tuesday into
Wednesday. Conditions across the waters will gradually improve
Wednesday night into the later part of the week as temperatures
across the interior cool and high pressure offshore builds into the
area.

&&

.CLIMATE...Today will be the first 80 degree plus day in Seattle
this year. The average date for the first 80 degree plus day in
Seattle is May 21st so we are right on schedule. Last year at this
time there had already been 8 days with highs 80 or more in
Seattle heading toward the record 9 days of 80 degrees plus days
in April and May.

The record high for Seattle today is 86 degrees set in 1969. In
Seattle the high has only been 80 degrees or greater today 5 times
since records started in 1945. Felton

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 6 PM this evening to 5 AM PDT
     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.

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

     Small Craft Advisory from midnight tonight to 6 AM PDT Tuesday
     for Central U.S. Waters Strait Of Juan De Fuca-East
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Gale Watch from Tuesday afternoon through late Tuesday night for
     Admiralty Inlet-Northern Inland Waters Including The San
     Juan Islands.

&&

www.weather.gov/seattle

You can see an illustrated version of this discussion at
www.wrh.noaa.gov/sew/gafd/latest_webafd.html