Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
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
000
FXUS66 KSEW 281049
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
349 AM PDT Sun May 28 2017

.SYNOPSIS...A strong upper level ridge over Western Washington
will move slowly east into Eastern Washington today into Memorial
Day. Daytime highs will remain well above normal through Memorial
day for the interior. Increasing onshore flow start to cool
temperatures on Monday with a more dramatic cool down on Tuesday.
Southerly flow aloft will also bring a chance of showers to the
area on Tuesday. Weak disturbances may bring a chance of showers
to the area into the end of the week.

&&

.SHORT TERM...Satellite imagery shows upper level ridge over the
area with low clouds along the coast, about half way down the
Strait of Juan De Fuca and on the south side of the Olympics as
far east as Shelton. Temperatures at 3 am/10z were in the upper
40s to lower 60s.

Upper level ridge remaining over the area today with the ridge
axis shifting over into Eastern Washington later today. Surface
gradients remain flat to weakly onshore. Temperatures aloft have
shown little change overnight and this trend will continue today
with 850 mb temperatures in the plus 14 to 16C range. With little
change in the pattern will go for a repeat of Saturday today with
high temperatures in the mid 70s to upper 80s over the interior
and 60s along the coast. The low clouds will burn back to the
beaches this morning but with the weak onshore flow the low clouds
could hang along the beaches all day.

Upper level ridge east of the area tonight and Memorial day.
Onshore surface gradients increase overnight with the gradients
remaining onshore during the day on Monday. Models have the
temperatures aloft remaining similar to todays readings with 850
mb temperatures within a degree or two of plus 16C. The marine
layer associated with the increasing onshore surface gradients
will be shallow with the low clouds overnight making a run at the
metro area but most likely will not get east of Puget Sound. With
the weak marine push will go for 5 to 10 degrees of cooling for
the interior on Monday putting highs mostly in the 70s while the
coast with the increasing onshore flow will see highs only near 60
with the low cloud cover hanging on longer.

Upper level ridge moving east Monday night into Tuesday with an
upper level trough approaching from the west. Onshore surface
gradients increasing resulting in a stronger marine push for the
interior. Flow aloft becoming southerly with the air mass
becoming somewhat unstable above the marine layer later in the day
on Tuesday. Models have been having a hard time timing the first
shortwave to get kicked out of the trough. This mornings model run
brings the shortwave up over the area later in the day on Tuesday.
The air mass will be unstable enough for at least a slight chance
of thunderstorms with the shower chances with the shortwave. The
combination of the marine push and the increasing cloud cover from
the shortwave will keep highs mostly in the 60s on Tuesday.

.LONG TERM...Extended models in good agreement for the first
couple of days with the upper level trough offshore pushing
shortwaves over the area at times Wednesday and Thursday. This
will keep at least a chance of showers in the forecast. Model
solutions start to diverge on Friday with the GFS building a flat
ridge over the area while the ECMWF keeps a trough over Western
Washington. The ECMWF does try to build a ridge over the area on
day 8. Current forecast splits the difference in the models with a
chance of showers continuing on Friday with just a chance of
showers over the Cascades on Saturday. High temperatures will
return back to near normal with 60s common through the extended
period. Felton

&&

.AVIATION...A ridge of high pres will remain over the region for
contd SW flow aloft. Expect the surface onshore pres gradient to
grdlly tighten during the day today. Meanwhile, widespread IFR CIGs
over the coast will lift into the MVFR category range during the day
today. Expect areas of LIFR CIGs and/or VSBYs east of KHQM and west
of a line from about KSHN-KOLM-KKLS to dissipate by 1800 UTC.

KSEA...VFR with light northerly winds through this evening. Winds
will become light and variable late tonight.

&&

.MARINE...
High pressure offshore along with lowering pressure east of the
Cascades will result in strengthening onshore flow through Tuesday.
This will lead to the potential for gale force winds over parts of
the Strait of Juan de Fuca tonight, Mon, and Tue. Gale force winds
appear likely tonight but there is some uncertainty in the timing.
It could happen as early as 8 PM PDT tonight or as late as 1 AM
Monday, hence the issuance of the Gale Watch.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Gale Watch from this evening through late tonight for Central
     U.S. Waters Strait Of Juan De Fuca-East Entrance U.S.
     Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 6 PM PDT this evening 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 6 AM PDT Monday
     for Admiralty Inlet-Northern Inland Waters Including The
     San Juan Islands.

     Small Craft Advisory from 3 PM this afternoon to 6 AM PDT Monday
     for West Entrance U.S. Waters Strait Of Juan De Fuca.

&&

$$

www.weather.gov/seattle

You can see an illustrated version of this discussion at
www.wrh.noaa.gov/sew/gafd/latest_webafd.html



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.