Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
FXUS66 KSEW 201614
Area Forecast Discussion
National Weather Service Seattle WA
914 AM PDT MON JUN 20 2016
.SYNOPSIS...A weak upper low just offshore will move through the
area tonight for a chance of showers. Weak high pressure will
build over the region Tuesday. Another upper level low will move
through the area Thursday and Thursday night. A weak upper level
ridge will build over Western Washington for the weekend.
.SHORT TERM...Southerly flow aloft from an upper level low
spinning just offshore, combined with moisture in the mid levels,
will continue to bring overcast to broken mid level clouds over
much of the interior of Western Washington today. There is a
chance of thunderstorms over the mountains late today but have not
expanded to the lowlands since the mid level cloud layer should
inhibit surface warming a bit. Highs today will be fairly typical
for this time of the year, in the mid 60s to mid 70s.
Tonight the upper level low offshore will move inland for a chance
of showers tonight. A short lived Puget Sound Convergence Zone
could set up as surface winds switch to the south overnight.
Tuesday will see some drying with zonal flow over the area. Expect
improving conditions through the day for partly sunny skies and
temperatures again near normal under onshore flow conditions.
Wednesday into Wednesday night a weak surface front will move
through the area for showers mostly on the coast and in the
mountains...and mostly cloudy skies elsewhere. Smith
.LONG TERM...Extended models in good agreement with the upper
level low approaching the coast Thursday afternoon. Low level
onshore flow and a destabilizing air mass will result in
increasing shower activity in the afternoon. With the cooling
aloft associated with the low and the afternoon precipitation
highs on Thursday will be cool for early summer...only in the 60s.
Upper level low moving through the area Thursday night into Friday
morning keeping showers in the forecast. Upper level ridge
building offshore Friday with drier northwesterly flow aloft
eventually taking over. Friday will be another cool day by first
week of summer standards with highs in the 60s and lower 70s.
General agreement in the models over the weekend with a ridge
building into Western Washington. The gfs and Canadian are more
aggressive with the ridge building with 500 mb heights rising into
the lower 580 dms. The ecmwf is a little weaker with the ridge
with 500 mb heights only in the mid 570 dms. All of the models are
dry. Will stay with current cool trend and go for highs closer
to the ecmwf guidance...70s for the most part...for Saturday and
.AVIATION...An upper level low is spinning off the WA coast this
morning with mid level clouds across Western Washington. VFR
conditions will prevail. There is a slight chance of thunderstorms
this afternoon, mainly over the Cascades where instability is the
greatest. The upper low will shift inland tonight for isolated to
scattered showers. MVFR conditions are likely early Tuesday
morning as the marine layer spreads inland. Otherwise, Tuesday
will be drier with weak ridging over the region. 33
KSEA...VFR conditions today with N winds at the surface. Winds
will flip to S/SW by 06Z with -SH in the vicinity. MVFR conditions
are possible by 09-12Z the the marine layer pushes inland. 33
.MARINE...Low level onshore flow will increase this afternoon and
evening as low pressure shifts into Eastern Washington. Small
Craft Advisory winds are expected over the Outer Coastal Waters,
Central/East Strait and Northern Inland Waters. Winds will ease
late tonight. A weak front will pass through the waters on
Wednesday. Onshore flow will prevail through the end of the week.
PZ...Small Craft Advisory until 3 AM PDT Tuesday 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.
Small Craft Advisory until 9 AM PDT Tuesday for Central U.S.
Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
Strait Of Juan De Fuca.
Small Craft Advisory from 6 PM this evening to 3 AM PDT Tuesday
for Northern Inland Waters Including The San Juan Islands.
Small Craft Advisory from 6 PM this evening to midnight PDT
tonight for Admiralty Inlet.
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