Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 271056
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
356 AM PDT FRI MAY 27 2016

.SYNOPSIS...A large upper level low will remain anchored over
British Columbia through this weekend.  A series of small weak upper
level shortwave troughs embedded in the flow around the main low
will bring scattered showers at times to western Washington.
Much warmer weather is expected beginning Memorial day and
continuing into the middle of next week as an upper level ridge
builds offshore then moves over western Washington.

&&

.SHORT TERM...Satellite imagery shows upper level trough over
western Washington early this morning. Doppler radar shows
scattered showers along the coast and showers in a convergence
zone over Snohomish and the northern King county. Temperatures at
3 am were in the mid 40s to mid 50s.

Little change in the pattern today with the upper level trough
remaining over the area keeping at least a chance of showers in
the forecast. Convergence in the lower levels will also continue.
Little change in the surface pattern or the flow aloft will
result in little movement of the convergence zone. Highest pops
over the area today will be in this area over Snohomish and King
counties. Low level onshore flow means plenty of cloud cover for
most of the area. Highs will remain below normal...in the mid 50s
to lower 60s.

Low level onshore flow and the convergence zone will dissipate
tonight as a weak shortwave spinning around the trough approaches
the coast turning the surface gradients southeasterly. Shortwave
will be near the coast by 12z Saturday keeping a chance of showers
in the forecast. Lows will be around 50.

Shortwave trying to move inland on Saturday but falls apart
before it gets east of the Puget Sound. Plenty of shower activity
on the coast Saturday. For the remainder of the area just a chance
of showers. Highs will continue to be on the cool side...mid 50s
to lower 60s.

Not much going on Saturday night. What is left of the shortwave
dragging across the area keeping a chance of showers in the
forecast. Lows once again near 50.

Last in the series of shortwaves moving into western Washington on
Sunday keeping a chance of showers in the forecast. Surface
pattern once again favorable for a convergence zone over Snohomish and
northern King county in the afternoon. Highs will remain below
normal...mid 50s to mid 60s.

.LONG TERM...Some changes to the forecast beginning Sunday night.
Model trends continuing with the idea of faster upper level ridge
development offshore with the upper level trough moving east
faster as well. Have dried out the forecast Sunday evening west of
Puget Sound and taken the pops out of the forecast overnight
Sunday night/Monday morning. Flow at the lower levels light Monday
morning and with plenty of low level moisture still around will be
hard to get rid of the cloud cover. By afternoon with the ridge
building in and the low level flow going northwesterly expect the sun
to break out. With more sunshine in the forecast have raised the
high temperatures a few degrees with the warmer locations getting
into the lower 70s. Rapid warm up still on tap for Tuesday as the
upper level ridge moves overhead and the low level flow goes
offshore as a thermally induced trough builds along the coast.
Warmer locations on Tuesday should reach the lower 80s. Another
warm day on Wednesday with the thermally induced trough moving
inland. Combination of the upper level ridge shifting east with
plenty of high level moisture moving over the area in southerly
flow aloft and a transition to light onshore flow at the surface
will result in some cooling on Thursday. Felton

&&

.AVIATION...An upper level trough over B.C. will extend south over
Washington through the weekend. moderate northwesterly flow aloft.
Strong low level onshore flow...easing Friday. Moist in the lower
levels and mostly stable. A Puget Sound convergence zone is possible
at times through tonight...mainly affecting the KPAE terminal.

Cigs 3-5K FT today with areas of MVFR this morning. MVFR cigs are
likely in the vicinity of the convergence zone...mainly affecting
KPAE.

KSEA...Mainly VFR cigs but MVFR is possible at times this morning.
Southwesterly wind 8-12 Kt.

&&

.MARINE...Onshore flow will gradually ease through Saturday...then
increase Sunday behind a weak front. Small craft winds are likely in
the Central and East Strait through tonight. The flow will
transition to offshore early next week.

&&

.SEW Watches/Warnings/Advisories...
WA...None.
PZ...Small Craft Advisory until 9 AM PDT this morning 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-West Entrance U.S. Waters
     Strait Of Juan De Fuca.

     Small Craft Advisory until 5 AM PDT Saturday 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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