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
000
FXUS66 KSEW 261622
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
922 AM PDT Mon Jun 26 2017

.SYNOPSIS...Onshore flow will bring a typical weather pattern of
night and morning clouds, with afternoon clearing and near normal
temperatures for the upcoming work week. An upper level trough will
move through the area over the weekend bringing a slight chance of
showers.

&&

.SHORT TERM...Satellite imagery this morning showing a mixed
bag of clouds, including mid and high clouds over a marine stratus
deck along the coast, central strait and much of the interior south
of Admiralty Inlet. Low cloud coverage over the interior will
continue to expand through mid morning before beginning to lift and
burn back to the coast around midday. Mid and high level clouds will
continue to stream into the area with the southwesterly flow aloft
today. Weak instability aloft coupled with an upper level short wave
moving into Oregon may be enough to product a few light showers,
especially over the south this morning. The instability and
dynamics over Oregon is resulting in a few weak Thunderstorms just
west of the Portland/Vancouver area this morning. While it is not
expected to affect the area this morning it does warrant mention and
will be monitored. Afternoon clearing will result in mostly sunny
skies for most of the interior. Lingering onshore flow will make it
clearing along the coast difficult. High temperatures today will be
near normal.

The overall weather pattern will remain in place through Wednesday
with late night and morning clouds and afternoon clearing over the
interior. Temperatures will remain near normal. On Wednesday, an
upper level ridge offshore will begin to build into the region while
flow at low levels remains onshore. This will set the stage for a
bit of warming, mainly Thursday into Friday.

.LONG TERM...from previous discussion...Extended models in good
agreement Thursday and Friday with the upper level ridge offshore
moving over the area. 500 mb heights rising into the lower 580 dms.
The low level flow will remain onshore both days. High temperatures
will be a few degrees warmer both days compared to the short term
with with 70s and lower 80s over the interior. With the onshore flow
highs on the Coast will remain in the 60s.

Model solutions inconsistent for the weekend with the GFs building
another ridge over the area for Sunday while the ECMWF brings a
trough into western Washington for the weekend with a weak
shortwave. The Canadian model is a compromise between the GFS and
ECMWF. The ECMWF solution has remained consistent for a few runs
while the ridging on the GFS is a somewhat new solution. The
forecast is more in line with the ECMWF solution at this point and
will stick with that idea in this package with mostly
cloudy/partly sunny skies and a slight chance of showers at some
point over the weekend. Highs will cool back down to near
normal, 60s to mid 70s. Felton

&&

.AVIATION...A slow moving weak upper level trof centered over
western Canada will prevail over the region thru this evening. SW
flow aloft will become W this evening. The low level flow will
remain strong onshore thru this evening. The air mass is weakly
unstable (above the marine layer) over SW WA this morning. There is
a slight risk of ISOLD tstms over Lewis County this morning.

Expect primarily MVFR CIGs (1-2K ft) to prevail over much of the
lower elevations this morning. The clouds are anticipated to scatter
out over the interior between 1800 and 2100 UTC. Areas of MVFR CIGs
will persist over the coast throughout the day.

KSEA...Expect MVFR CIGs this morning. It looks like the stratus may
hang around later than the current TAF indicates, possibly as late
as 2000 UTC. Look for low clouds (MVFR CIGs) to return late tonight
or after 2 AM PDT. Winds will be S or SW 5-13 knots, strongest this
afternoon and evening.

&&

.MARINE...
High pres offshore with lower pres E of the Cascades will result in
onshore flow through midweek. The flow will be the strongest through
this evening.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Gale Warning until midnight PDT tonight for Central U.S.
 Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of
Juan De Fuca.

 Small Craft Advisories are in effect for parts of the coastal
waters, the west entrance to the Strait of Juan de Fuca, and the
Admiralty Inlet.

&&

$$

www.weather.gov/seattle

An illustrated version of this forecast discussion can be seen 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.