Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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
000
FXUS66 KSEW 251635
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
935 AM PDT Sun Jun 25 2017

.SYNOPSIS...Upper level ridging over the region will
result in one more very warm, and dry day for much of the area
today. Offshore flow will transition to onshore this afternoon and
evening helping cool temperatures along the Coast but not early
enough to keep the interior from reaching near record levels. Much
cooler temperatures will settle into the interior Monday with
morning clouds as onshore flow and a marine air mass return for the
week.

&&

.SHORT TERM...Satellite imagery shows clear skies over Western
Washington save for the odd mid and upper level cloud streaming over
the upper level ridge axis. Stratus has worked north along the
Oregon coast to the mouth of the Columbia River and Long Beach in
Southwestern Washington as of 15z this morning.

The thermally induced surface trough along the Coast will shift
inland this afternoon helping cool the coast while much of the
interior remains on track for potentially record breaking high
temperatures. 850 mb temperatures are expected to reach as high as
24 C this afternoon with light winds over the area as the thermally
induced surface trough shifts inland. This will combine to help bump
temperatures over the interior by about 5 degrees over yesterday for
most areas, rising into the mid 80s over the Northwest Interior and
the mid to upper 90`s over the Southwest Interior...on track for
record breaking levels especially over the southern half of the
area. Accordingly the heat advisory remains in effect until this
evening from about Seattle southward, including the foothills.

Marine air will push into the interior tonight into early Monday
morning as the surface trough shifts east of the area. Forecast KOTH-
KSEA surface gradients expected to rise into the 5 to 6 mb range
driving stratus along the Coast tonight through the strait into the
north interior as well as through the lower Chehalis valley into the
southern portion of the Hood Canal and Puget Sound area. Lows will
dip into the 50s and lower 60s. Morning stratus and a marine air
mass will result in much cooler, near normal, temperatures on
Monday. Late night and morning clouds will return Monday night into
Tuesday with afternoon sunshine for the interior and near normal
highs again Tuesday.

.LONG TERM...from previous discussion...Extended models in pretty
good agreement but not showing much run to run consistency for
Thursday onward. On Wednesday low level onshore flow continuing with
the weak trofiness aloft coming to an end with an upper level ridge
beginning to build off the Coast. Models are a little faster on the
00z run moving this upper level ridge through Western Washington on
Thursday followed by a dissipating front late Friday into Saturday.
Both the ECMWF and GFS have some light precipitation over the area
late in the period which is a departure from the runs last night
which had an upper level ridge building over the area on Friday and
Saturday. Will not add any chance pops for the forecast for Friday
night and Saturday in this forecast package with the inconsistent
model solutions but will add some more cloud cover and lower high
temperatures a touch for next Saturday back down to near normal. For
Thursday and Friday continuing onshore flow will lead to some
morning cloud cover and highs near normal, mid 60s to mid 70s. Felton

&&

.AVIATION...An upper level ridge over the region will slowly move
E, allowing an upper level trof to approach British Columbia. The
flow aloft will be from the SW. Low level offshore flow will become
onshore this afternoon and then strengthen tonight. Expect stratus
(IFR CIGs) and areas of fog (MVFR VSBYs) to move over the coast
early this evening, grdlly overspreading parts of the interior
lowlands overnight.

KSEA...VFR til about 1000 UTC (3 AM PDT). After 1000 UTC, expect
MVFR CIGs (1-2K ft) to move over the terminal from the south. CIGs
may lower into the IFR category range (700-900 ft) Monday morning.
Light W or NW winds will become southerly near 10 knots late tonight
or after 0600 UTC (11 PM PDT).

&&

.MARINE...
A thermally induced trough of low pres along the coast will shift E
of the Cascades this afternoon, causing the flow to become onshore
or westerly. The flow will strengthen tonight for gale force winds
over parts of the Strait of Juan de tonight. Strong onshore flow
will persist Monday before weakening on Tuesday.

&&

.CLIMATE...Record highs are forecast for Seattle ( record 88 set
in 2006 ), Olympia ( record 90 set in 2015 ) and Bellingham (
record 83 set in 2015 ). A record high is also possible at
Quillayute ( record 81 set in 2000 ).

The warmest June day on record at Seattle-Tacoma airport is 96
degrees on June 30th, 1995 and June 9th, 1955. Records started at
the airport in 1945.

The warmest June day on record in Olympia is 98 degrees on June
18th, 1982.

With Seattle-Tacoma airport still at 71 degrees at 3 am there is a
chance a new high minimum temperature for the day will be set. The
record is 62 degrees set in 2006. The warmest minimum temperature
on record for Seattle in June is 67 degrees set on June 26th,
2006.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Heat Advisory until 9 PM PDT this evening for Bellevue and
     Vicinity-Bremerton and Vicinity-East Puget Sound Lowlands-
     Hood Canal Area-Seattle and Vicinity-Southwest Interior-
     Tacoma Area.

PZ...Gale Warning from 6 PM this evening to 9 AM PDT Monday 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 much of the coastal
 waters, the west entrance to the Strait of Juan de Fuca,
 and the Northern Inland Waters.

&&

$$

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.