Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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406
FXUS66 KSEW 261044
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
344 AM PDT THU MAY 26 2016

.SYNOPSIS...An upper trough will move into the area today. Another
trough will arrive over the weekend. These features will keep
showers in the forecast through the Memorial Day weekend. An
improving trend will start on Memorial day as an upper level ridge
builds offshore. Sunnier and much warmer weather is expected
beginning Tuesday as the ridge moves inland.

&&

.SHORT TERM...Satellite imagery shows cloudy skies over western
Washington early this morning with an upper level trough digging
south down the British Columbia coast. With the cloud cover
temperatures were in a narrow range at 3 am...upper 40s to mid
50s.

The upper level trough will continue to dig south today reaching
western Washington late in the day. Low level onshore flow will
increase ahead of the trough reducing the chances for much in the
way of sunshine. Not much moisture associated with the trough
initially but with a deep layer of low level moisture present the
little bit of lift with the arrival of the trough could set off a
few showers. Temperatures will continue to be on the cool side for
late May with highs only in the upper 50s to lower 60s.

Trough remaining over western Washington tonight. Increasing
onshore flow will result in gale force winds for the central and
Eastern Strait of Juan de Fuca. A chance of showers will remain in
the forecast with the trough overhead. The exception to this is
in the convergence zone which will form early this evening
over Snohomish county. With the strong flow through the strait
and west northwesterly flow in the lower levels the convergence
zone could move into northern King county as well this evening.
Will put higher pops in the convergnece zone location. Lows
tonight will be in the upper 40s and lower 50s.

Trough remaining over western Washington keeping showers in the
forecast Friday. Low level convergence pattern continuing with
the best chance for showers in the central Puget sound region.
Plenty of onshore flow will keep skies cloudy. It will be another
cool day with highs a couple of degrees either side of 60. Snow
levels will get down to near 4500 feet...below the summit of the
higher passes...North Cascades and White.

One trough kicks east Friday night with another trough replacing
it on Saturday keeping the forecast cool with at least a chance of
showers.

.LONG TERM...Extended models in good agreement on Sunday with
the trough remaining overhead with another shortwave moving
through the area. Some differences in the models on Memorial day.
The ecmwf is quicker to build the upper level ridge offshore and
dry out western Washington. The gfs leaves the upper trough in the
vicinity in the morning. Have gone ahead and changed the forecast
for Monday to dry the afternoon out. The models are back in
agreement on Tuesday with a rapid warm up as the upper level
ridge offshore moves over western Washington and a thermally
induced trough develops along the coast resulting in good offshore
flow for the area. Increased the high temperatures on Tuesday into
the 70s for most of the area. On Wednesday both models show the
upper level ridge shifting east with the ecmwf stronger with the
ridge. Low level flow goes weakly onshore during the day. For now
have only cooled down the temps along the coast significantly for
Wednesday with another warm day for the interior. Felton

&&

.AVIATION...An upper level trough over B.C. will dig southward
and brush Washington this afternoon and tonight.
Light westerly flow aloft...becoming moderate northwesterly flow
this afternoon and tonight. Low level onshore flow persists.
The air mass is stable with moisture mostly in the lower
levels...becoming somewhat unstable tonight. A Puget
Sound convergence zone is likely by late afternoon or
evening...possibly affecting the KPAE/KSEA/KBFI terminals with
shifting winds and showers.

Cigs are variable but mostly above 3K FT early this morning. While
some scattering and lifting of clouds occurred
overnight...MVFR cigs are still expected to fill back in and expand
this morning. By afternoon...cigs lifting to 3-4K FT. Areas of MVFR
expected later tonight.

KSEA...Cigs 3-4K FT lowering to around 2500 FT this morning...then
lifting to above 3K FT after 20z. Southwest
wind 7-10 KT...rising to 10-12 KT w/ gusts 22 KT this morning. Winds
swinging around to west or even Northwest this evening with
convergence zone showers over or just north of the terminal. DTM

&&

.MARINE...Onshore flow will strengthen again this afternoon and
evening. Westerly Gales are likely to develop in the Central/E
Strait this afternoon...w/ Small craft strength southwesterly winds
in the south part of the North Inland waters and northwest winds in
Admiralty Inlet tonight.

The onshore pattern will repeat Friday into the weekend...but
gradually weaken. Northerly or offshore flow may develop early next
week. DTM

&&

.SEW Watches/Warnings/Advisories...
WA...None.
PZ...Small Craft Advisory until 1 PM PDT this afternoon for Central
     U.S. Waters Strait Of Juan De Fuca-East Entrance U.S.
     Waters Strait Of Juan De Fuca.

     Gale Warning from 1 PM this afternoon to 5 AM PDT Friday for
     Central U.S. Waters Strait Of Juan De Fuca-East Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 5 AM PDT Friday 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.

&&

$$

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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