Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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795
FXUS66 KSEW 261102
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
402 AM PDT MON SEP 26 2016

.SYNOPSIS...A strong upper ridge will move across the area today for
a warm and mainly sunny day. A weak cold front will bring a chance
of light precipitation tonight and Tuesday morning. Expect partly
to mostly sunny days Tuesday afternoon through Thursday with dry
southwest flow aloft. An upper level trough will bring cool
showery weather Friday through the weekend.

&&

.SHORT TERM...Satellite imagery shows some high clouds over
Western Washington early this morning. Cold front to the northwest
just moving through Haida Gwaii at 10z/3am. Temperatures around
the area are in the 50s and lower 60s.

Upper level ridge over the area early this morning shifting east
with the ridge axis into Montana by 00z Tuesday. Surface gradients
are offshore early this morning with even the cross cascade
gradient negative ( SEA-EAT and SEA-YKM both near -1 mb ).
Sandpoint profiler confirms what the models have been indicating
the last few days...the warmest air in the lower levels will be
over the area today. Current temperatures on the Sandpoint
profiler at 2000 feet above the surface plus 20c with 850 mb temps
plus 18c. Surface gradients turning back onshore this afternoon
with some weak surface ridging out ahead of the approaching cold
front. This will keep high temperatures along the coast near 70
degrees. For the interior the transition to onshore flow will not
be early or strong enough to prevent today front being a couple
of degrees warmer than yesterday with highs in the 70s and lower
80s. Record high in Seattle is 78 and the record at Olympia is 81
degrees. Both of these records are in jeopardy today.

Marine push tonight with the cold front reaching the northwest
corner of the state after midnight. Front running into the back
side of the upper level ridge and will weaken considerably
overnight. Not enough to take the chance of precipitation out of
the forecast yet...but if the model trends continue later
forecasts will be dry for tonight. Lows will be in the upper 40s
to mid 50s.

Front through the area early Tuesday morning. Surface gradients
turn northwesterly with the lower levels of the air mass drying
out quickly. Have reduced the cloud cover for Tuesday afternoon
and added a couple of degrees to the high temperatures pushing
them up into the lower 70s in the warmer locations.

Not much going on Tuesday night and Wednesday. Cold upper level
trough digging south well offshore. Surface gradients remain
northwesterly with dry southwesterly flow aloft. Wednesday looks
to be mostly sunny with highs once again in the 60s and lower 70s.
With the lack of cloud cover and light surface gradients Tuesday
night will be a little chilly with the colder locations dropping
into the upper 30s.

.LONG TERM...Extended models starting to show more consistency in
their solutions for the upper level trough. 00z runs have
the trough continuing to dig south offshore on Thursday for
another dry day. The trough moves east on Friday and into Western
Washington over the weekend resulting in cool and showery weather.
Highs next weekend will be in the lower 60s at best. The air mass
will cool considerably late in the week with the snow levels near
5000 feet for the weekend. This means Paradise on Mount Rainier
as well as the higher passes like the North Cascades highway could
see a little snow. Outside of the forecast window the models are
also consistent in showing very fall like weather after the
weekend with a series of fronts moving into the area. Felton

&&

.AVIATION...An upper ridge and surface high pressure will shift
inland today. A cold front will move through Western Washington
tonight. The air is dry and stable, there will be some cirrus and a
few patches of fog in the sheltered valleys, and then clouds will
increase late this afternoon or evening ahead of the front.

KSEA...Some cirrus at times, a northerly breeze. Clouds arrive
tonight with marine air and a cold front.


&&

.MARINE...Light offshore flow will turn westerly this afternoon on
the coast and in the Strait, and strengthen tonight as a cold front
moves through Western WA. This could result in gale force westerlies
over the central and eastern portion of the Strait of Juan de Fuca
where a Gale Watch is in effect. Onshore westerly flow will turn
more northerly and decrease Tuesday.

&&

.CLIMATE...Today will be the last shot at 80 degree weather for
Seattle this month. So far there has not been an 80 degree plus
day in the month of September. The last year were there wasn`t an
80 degree plus day for the entire month of September was 2005.
Felton

&&

.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 from noon today to 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.

&&

$$

www.weather.gov/seattle

You can see an illustrated version of this discussion at
www.weather.gov/seattle/gafd/latest_webafd.html



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