Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

FXUS66 KSEW 270318

Area Forecast Discussion
National Weather Service Seattle WA
818 PM PDT SUN JUN 26 2016

.SYNOPSIS...An upper ridge will bring mostly sunny warm weather
again on Monday. Isolated thunderstorms are possible over the
mountains Monday afternoon and evening as an upper level
disturbance passes across the area. Marine clouds will increase
on the coast Monday night and there will be areas of morning
clouds on Tuesday. Mostly sunny days are expected Wednesday
through Friday with some clouds at times on the coast. The weather
will probably be cooler and cloudier next weekend.


.SHORT TERM...A short wave upper ridge is passing eastward across
Western Washington this evening and will move through Eastern
Washington on Monday.

A short wave upper trough over the offshore waters will move
inland during the day on Monday giving some instability and a
chance of thunderstorms to the mountains during the afternoon and
evening hours. Lifted indices in the mountains approach -4 in the
afternoon while MU CAPE values exceed 2500 J/kg per the GFS.
While conditions over the mountains late Monday afternoon are
quite unstable and there will be a chance of thunderstorms there,
only the GFS shows a 30-40 percent chance of convection moving
from the Olympics and coastal terrain into the interior lowlands
Monday afternoon and evening. The ECMWF and NAM are dry. Will wait
to see what the complete 00Z suite of guidance says before
expanding the thunderstorm chances for the interior lowlands.

Pressures rise from the west Monday evening behind the upper
level disturbance. This should allow marine air to push nicely
into the interior Monday night and Tuesday morning, and provide
for about 5 degrees cooling on Tuesday.

Another weak short wave trough will pass across the area Tuesday
evening resulting in another surge of marine air pushing inland.
Temperatures should cool another 2-4 degrees on Wednesday.

Forecasts will be modified slightly to add some clouds to the
mountains Monday afternoon and evening and to modify the cloud
cover amounts Monday night into Tuesday. Otherwise forecasts look
like they are in good shape. Albrecht

.LONG TERM...Longer range models shift the upper ridge from the
Four Corners region and Western Montana eastward to about 100-105
degrees longitude by next weekend. This shift and the development
of some ridging along 150W will allow a weak upper trough to drop
into the Pacific Northwest and persist through the Independence
Day weekend. This should result in an increase in night and
morning marine moisture in the interior, cooler temperatures -to
about 2-4 degrees below normal- and perhaps a few showers by later
in the weekend. The long range forecast was earlier nudged in that
direction and will be maintained for now. Albrecht


.AVIATION...An upper ridge over Eastern Washington will shift over
Western Montana on Monday. A mostly dry upper short wave will
move through Western Washington Monday afternoon and evening in
southwest flow aloft. At the surface, onshore flow will prevail
with high pressure offshore and lower pressure inland. Onshore
flow will increase late Monday as the upper short waves moves

The air mass is dry and stable. Mid level moisture will increase
slightly on Monday and the air mass will become unstable,
especially over the mountains. Schneider

KSEA...High clouds at times. Northerly wind 5-10 knots. Schneider


.MARINE...Onshore flow will prevail through Friday with high
pressure offshore and lower pressure inland. Small craft advisory
west winds are expected 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 Monday, aided by a passing upper
short wave. This could bring gale force west winds to the Central
and Eastern Strait Monday evening. A gale watch has been issued
for this possibility. 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


.SEW Watches/Warnings/Advisories...
PZ...Small Craft Advisory until 2 AM PDT Monday 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 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 Monday afternoon through late Monday night for
     Central U.S. Waters Strait Of Juan De Fuca-East Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 1 AM PDT Monday for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.



You can see an illustrated version of this discussion at is the U.S. government's official web portal to all federal, state and local government web resources and services.