Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
FXUS66 KSEW 271000
Area Forecast Discussion
National Weather Service Seattle WA
300 AM PDT MON JUN 27 2016
.SYNOPSIS...An upper ridge will bring sunny warm weather to
Western Washington today. Isolated afternoon and evening
thunderstorms are possible over the mountains. Fair weather will
continue Tuesday through Friday with mostly sunny days, night and
morning clouds mainly at the coast, and temperatures a little
above normal. Cooler cloudier weather is likely next weekend.
.SHORT TERM...Southwest flow aloft continues over Western
Washington early this morning,as an upper ridge builds and moves
slowly east toward the Rocky Mountains. Light northerly flow
prevails at low levels. The air mass is dry with clear to partly
cloudy skies, except for areas of marine stratus along the coast
and over the coastal waters. Temperatures at 2 am ranged from 51
at Quillayute to 69 at Vancouver.
The upper ridge will move to the Rocky Mountains today. A small
shortwave trough -- currently along 130W -- will move northeast
across Western Washington late today, probably triggering isolated
thunderstorms over the Olympics and Cascades. For the lowlands it
should be another generally sunny day, and the morning stratus
along the coast should be short lived. Highs today will be roughly
1 to 3 degrees higher than yesterday in the interior. It will be
slightly cooler along the coast, as onshore flow develops in
response to the upper shortwave.
Light and dry southwest flow aloft will continue tonight. The
increase in onshore flow will deepen the marine layer along the
coast and stratus should be more widespread. Stratus should move
into the interior overnight, through the Chehalis Gap into the
south Puget Sound region and south interior and through the Strait
of Juan de Fuca. The large-scale ridge over the area will build
Tuesday, with 500 mb heights rising to around 5850 meters. So
stratus should burn back to the coast in the morning, and highs
will be mainly in the 70s to lower 80s.
There will be little change in the pattern Tuesday night and
Wednesday, with dry southwest flow aloft and weak to moderate
onshore flow with a shallow marine layer at the surface. Aside
from late night and morning stratus mainly at the coast, Wednesday
will be another sunny day with highs mostly in the 70s to lower
.LONG TERM...Upper heights over the region will fall beginning
Wednesday night and Thursday and probably continue through the
weekend, as the Four Corners high weakens and a a series of minor
troughs move into British Columbia and the Pacific Northwest. The
change in the weather should be fairly gradual, with mostly sunny
weather on Thursday and Friday and high temperatures only a few
degrees lower. Troughiness will probably deepen over the weekend,
and the latest run of both the GFS and ECMWF suggest that our
forecast -- especially for Sunday -- might be optimistic. McDonnal
.AVIATION...A dry upper short wave will move through Western
Washington this afternoon and evening in southwest flow aloft.
Weak high pressure aloft will move over the area tonight. At the
surface, onshore flow will prevail with high pressure offshore and
lower pressure inland. Onshore flow will increase late today as
the upper short waves moves through.
The air mass is dry and stable. Mid level moisture will increase
slightly today and the air mass will become unstable, especially
over the mountains. Areas of stratus should remain confined to the
coast and locally down the Strait this morning. Stratus will
spread partially into the interior tonight. Schneider
KSEA...High clouds at times today with northerly wind 5-10 knots.
There is a chance stratus could reach the terminal after sunrise
Tuesday morning. The wind should become light southerly early
Tuesday morning. Schneider
.MARINE...Onshore flow will prevail through Friday with high
pressure offshore and lower pressure inland. Small craft advisory
west winds should occur for the Central and Eastern Strait each
day. There will also be small craft advisory northwest winds over
the coastal waters at times, with the strongest winds generally in
the late afternoon and evening hours.
Onshore flow will increase later today, aided by a passing upper
short wave. This will likely bring gale force west winds to the
Central and Eastern Strait tonight. A gale warning has been
issued. Gale force winds are possible again for the Strait
Tuesday evening and pretty much every evening for the remainder of
the week as moderate to strong onshore flow continues. Schneider
PZ...Small Craft Advisory from 5 PM this afternoon to 11 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 from 5 PM this afternoon to midnight PDT
tonight for Coastal Waters From James Island To Point
Grenville Out 10 Nm-Coastal Waters From Point Grenville To
Cape Shoalwater Out 10 Nm.
Gale Warning from 5 PM this afternoon to 3 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 5 PM this afternoon to 3 AM PDT
Tuesday for Admiralty Inlet-Northern Inland Waters
Including The San Juan Islands.
You can see an illustrated version of this discussion at