Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 251026
AFDSEW

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

.SYNOPSIS...High pressure aloft will bring one more very warm day
to Western Washington today. Low level offshore flow will turn
onshore this afternoon and evening cooling temperatures down on
the Coast. For the interior today will be the hottest day. Much
cooler temperatures with some night and morning clouds will
prevail Monday and continue through the week with low level
onshore flow.

&&

.SHORT TERM...Satellite imagery shows clear skies still prevail
across Western Washington early this morning. Stratus just off the
coast has made it as far north as about Cannon Beach on the North
Oregon Coast. Temperatures at 3 am/10z were quite mild, in the
mid 50s to lower 70s in the Seattle metro area.

Record breaking high temperatures expected over the interior
today. Forecast for today still on track with the thermally
induced surface trough currently along the Coast moving inland
this afternoon. Model 850 mb temperatures for 00z this afternoon
range from plus 20 to plus 24C over the area, a couple of degrees
warmer than yesterday. Sandpoint profiler has east winds above 400
meters all the way to 1400 meters with a nice little core of
20-25 knot easterlies around 600 meters. With the thermally
induced trough over the interior in the afternoon winds will be
light. All of these variables add up to a warmer day in the
interior versus Saturday by about 5 degrees for most areas. This
puts highs in the mid 80s over the Northwest Interior to the mid
and upper 90`s over the Southwest Interior. The heat advisory will
remain in effect from about Seattle southward including the
foothills until this evening. High temperatures on the Coast will
be tricky today with the switch to onshore flow during the day.
Highs along the coast will occur in the middle of the day. With
the flow turning onshore along the central Coast first have highs
about 5 degrees cooler versus the north Coast with 70s for the
central Coast and as high as mid 80s for the north Coast.

Marine air rushing inland tonight into early Monday morning
with the thermally induced surface trough east of the area. Model
surface gradients tonight have the KOTH-KSEA gradient peaking in
the plus 5 to 6 mb range with the KHQM-KSEA gradient peaking in
the 2.5 to 3.5 mb range. Stratus along the Coast tonight will move
through the lower Chehalis valley into the southern portion of the Hood
Canal and into the Puget Sound area. To the north the stratus will
make a run down the Strait of Juan De Fuca. Lows will be in the
50s and lower 60s.

Much cooler on Monday with the marine air in place over the area.
Onshore gradients relax but remain intact on Monday so even with
afternoon sunshine over the interior high temperatures will return
back to near normal, mid 60s to mid 70s. Along the Coast with a
deeper marine layer highs will only be in the lower to mid 60s.

Little change in the pattern Monday night and Tuesday with weak
trofiness aloft and low level onshore flow result in late night
and morning clouds with some afternoon sunshine for the interior
on Tuesday. Highs will be in the 60s and lower 70s.

.LONG TERM...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...A strong upper ridge axis will exit east across
Central Washington today and on to the northern Rockies tonight.
Light west flow aloft will become southwest today. Weak low- level
offshore flow and a dry air mass will continue this morning. Low-
level onshore flow will develop this afternoon, and the low-
level air mass will start to moisten tonight. Clear skies through
the day. Currently watching a southerly surge of marine clouds
moving north along the Oregon coast. It is already approaching
the coast near Astoria, so marine stratus will come surging into
Grays Harbor by this evening, spreading inland overnight tonight.

KSEA...Clear skies and light north wind will persist through
this evening. A shift to southwest surface wind is then expected
late this evening around 06z. This will bring IFR marine stratus
to the terminal for a few hours just after sunrise on Monday.
Haner

&&

.MARINE...A somewhat diffuse thermal pressure trough will linger
near the coast until after sunrise, leading to weak low-level
offshore flow. The trough will move east of the Cascades this
afternoon, opening the door to increasing onshore gradients and
wind. Forecast UIL-BLI pressure gradients are marginal for gales
in the Strait tonight, but hot temperatures over the interior this
afternoon favor westerly gales in the Strait tonight. So after
coordination with Environment Canada, opted to go with a Gale
Warning for the central and eastern Strait tonight. Another round
of gales is possible on Monday evening, then moderate onshore flow
will prevail for much of the week ahead.  Haner

&&

.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...Small Craft Advisory from noon today to 3 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 Point Grenville To Cape
     Shoalwater 10 To 60 Nm.

     Small Craft Advisory from 4 PM this afternoon to 10 PM PDT this
     evening for Coastal Waters From Cape Flattery To James
     Island Out 10 Nm-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 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.

&&

$$

www.weather.gov/seattle

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


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