Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 231623
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
923 AM PDT FRI SEP 23 2016

.SYNOPSIS...A weak front will move inland today for some rain. A
strong ridge will bring dry and warmer weather Saturday through
Monday with the warmest weather in September possible on Monday. A
marine push will cool things down on Tuesday. Upper level trough
moving out of the Gulf of Alaska in the middle of the week will
bring a threat of more rain to the area by late in the week.

&&

.SHORT TERM...Cloudier, cooler and wetter weather on tap today as
a cold front moves inland. Most areas are already seeing rain this
morning. The back edge of the cold front will reach the coast
around 18z with showers mainly affecting the Cascades this
afternoon and evening. The cooler marine air will keep
temperatures mainly in the 50s to lower 60s this afternoon.

An upper level ridge will start to build inland on Saturday for
drier weather. Low level clouds will likely linger through the
morning hours...then skies becoming partly to mostly sunny in the
afternoon. Temps will nudge upwards with highs closer to normal -
mid to upper 60s.

The upper level ridge will continue to build over the Pac NW on
Sunday...then start to shift east and inland on Monday. Both days
will be dry and mild with temperatures trending above normal. 33

.LONG TERM...Previous discussion...Extended models in good
agreement early on in the extended period with the low level flow
turning offshore briefly on Monday before the flow turns back to
onshore during the day. Upper level ridge shifting east of the
area on Monday but 850 mb temperatures peak on Monday, in the plus
13 to 16c range. The little bit of offshore flow in the morning
will help temperature get off to a warm start. Expect Monday to be
the warmest day in the forecast period...except on the coast where
the transition to onshore flow will take place by Monday afternoon
capping high temperatures near 70. For the remainder of the area
highs in the 70s and lower 80s.

Onshore flow continuing Monday night into Tuesday. Model
consistency starts to break down on Tuesday with the GFS bringing
a very weak shortwave into the area while the ECMWF does not have
this feature. Either way with the marine push Monday night Tuesday
will be much cooler with highs as much as 15 degrees lower than on
Monday, mostly in the 60s. Both models show an upper level trough
digging well offshore on Wednesday. The GFS keeps the trough
offshore on Thursday while the ECMWF moves the trough into Western
Washington. Did not add any pops to the forecast for the interior
on Thursday but did increase the cloud cover. Highs in the 60s
will be common both for Wednesday and Thursday. Felton

&&

.AVIATION...A weak occluded front off the coast will move inland
this afternoon. This front will mostly dissipate before reaching
the Cascades this evening. Expect a weak upper level trof of low
pres to move across the region this evening. Wly flow aloft will
strengthen and become NW this evening. Low level sly flow will
become wly behind the front.

Meanwhile, areas of MVFR CIGs will become more widespread this
afternoon. Expect areas of MVFR VSBYs, mainly with rain. The mtns
will be obscd.

KSEA...Expect VFR CIGs to lower into the MVFR category range this
afternoon. Winds will increase from the S at 10-15 knots with ocnl
gusts near 20 knots after 1800 UTC.

&&

.MARINE...An occluded front over the Washington coastal waters
will continue moving east but is anticipated to mostly dissipate
before reaching the Cascades this evening. Southerly will become
westerly behind the front. The flow will become nearly flat
Saturday night and then northerly on Sunday.

&&

.SEW Watches/Warnings/Advisories...
WA...None.
PZ...Small Craft Advisory until 5 PM PDT this afternoon for Admiralty
     Inlet-Coastal Waters From Cape Flattery To James Island 10
     To 60 Nm-Coastal Waters From Cape Flattery To James Island
     Out 10 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-Coastal Waters From Point
     Grenville To Cape Shoalwater Out 10 Nm-Northern Inland
     Waters Including The San Juan Islands-Puget Sound and Hood
     Canal-West Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory for hazardous seas from 5 PM this afternoon
     to 2 AM PDT Saturday for Coastal Waters From Cape Flattery
     To James Island 10 To 60 Nm-Coastal Waters From Cape
     Flattery To James Island Out 10 Nm-Coastal Waters From
     James Island To Point Grenville 10 To 60 Nm-Coastal Waters
     From James Island To Point Grenville Out 10 Nm-Coastal
     Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm-
     Coastal Waters From Point Grenville To Cape Shoalwater Out
     10 Nm.

     Small Craft Advisory for rough bar until 11 PM PDT this evening
     for Grays Harbor Bar.

     Small Craft Advisory until 5 PM PDT this afternoon for Coastal
     Waters From James Island To Point Grenville Out 10 Nm.

     Gale Warning until 11 AM PDT this morning for Coastal Waters
     From James Island To Point Grenville Out 10 Nm.

     Small Craft Advisory until 2 AM PDT Saturday for East Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 5 PM this afternoon to 2 AM PDT
     Saturday for Central 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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