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Area forecast discussion...updated 
National Weather Service Portland or
1203 am PDT Tuesday Oct 13 2015

Updated marine discussion and wwa section

Synopsis...a weak cold front will bring some light rain to
southwest Washington and extreme north Oregon coast tonight.
For the remainder of the forecast area clear skies will allow
fog develop in the valleys. An upper level ridge will strengthen
Tuesday and maintain dry and warmer weather through late
Friday...though some local morning fog will still be possible. There
is a chance of rain for next weekend.


Update...satellite shows stalled front hanging off the South
Washington and far north Oregon coast this evening. Radar shows weak
returns associated with the front while rain gauges have around 0.10
inch in part of SW Washington. There is also some light rain in the
Astoria area but in Tillamook it is already clear. Latest hrrr model
shows the front moving a little south and east overnight...reaching
further inland not passing the Coast Range. For the remainder of
the area expect radiational fog to develop in the valleys. However
some clouds may reach the north Willamette Valley and interior of SW
Washington limiting fog development.

Previous discussion from this afternoon...
short term...tonight through Thursday...visible satellite imagery
shows the last few pockets of this mornings dense fog dissipating
over the north Willamette Valley and Clark County early this
afternoon. A swath of clouds associated with a weak cold front
remains fixated on southwest Washington...but the main rain band is
situated just north of the forecast area border. 12z models show some
precipitation trickling down near Astoria later this evening...before the
cold front pushes inland and dissipates early Tuesday morning. Total
accumulate precipitation for this frontal band is around 0.10" for far southwest
Washington through Tuesday morning.

Expect a near repeat of fog Tuesday and Wednesday morning for the
coast and valley as light surface flow persists. A strong upper ridge
begins to build over the area Tuesday which will bring
dry...sunny...and warm weather through Thursday. Temperatures are
prognosticated to stay above our normal 60-65 degree through much of this
week...with inland highs expected in the lower to middle 70s. By
Wednesday night...dry easterly winds develop as thermal troughing
pushes north...which should inhibit any fog development for Thursday
morning. /27

Long term...Thursday night through Monday...upper level ridging
continues into Friday...keeping widespread dry and sunny conditions
under easterly flow over the region. Heights begin to decrease Friday
ahead of the next system dropping out of the Gulf of Alaska...which
reaches our coastline early Saturday. Enjoy Friday as it looks like
it will be the last sunny...dry...warm day before wet conditions
arrive for the weekend. The main push of rain will occur on
Saturday...then expect light rain under onshore flow to prevail
through Sunday morning. High pressure noses in over the eastern
Pacific late Sunday...which would hint at a drying trend for Sunday.
Another frontal system rides over the ridge...bringing another threat
for precipitation by next Monday...but models differ on the overall strength
of this system. Went more towards climatology pop for early next
week...with 25-35% pop expected. /27


Aviation...clear skies across most of our area. Dissipating front
has brought IFR ceilings and visible to kast with -ra. Ceilings and visible
could lower to LIFR with continued -ra or -dz early Tuesday
morning. Will see clouds from this front make their way into the
far north Willamette Valley...keeping fog patchy in this
area. Stratus from this front moves in around 4500 feet and could
lower to MVFR around 2500 feet Tuesday morning. Further south
expect less fog than last night as conditions seem to be drier.
Ksle and keug could still see fog bring ceilings and visible down to
IFR/LIFR just before sunrise...but confidence is lower. Along the
central Oregon coast the dissipating front approaching may allow
some fog or low stratus to develop and push onshore...but winds
along the coast in this area are forecast to turn offshore later
tonight which will try to keep this fog or low stratus off the
coast. Offshore winds may prove to be too weak...which would bring
LIFR ceilings and visible to konp later tonight through Tuesday morning.

Kpdx and approaches...VFR conditions tonight with clouds moving in
around 4500 feet. There is a moderate chance ceilings could lower down
to 2500 feet around 13z. Ceilings should start to clear out around 18z
with mostly clear skies Tuesday afternoon. -McCoy


Marine...have updated the forecast as seas at buoy 89 are coming
in around 14 feet at 13 seconds under a west-northwest swell. This
is running about 3 feet higher than guidance. Standard decay rate
will only see them drop around a foot for the inner waters. Still
not seeing the same increase at buoy 50 where seas are at 9
feet 12 seconds but do expect there will be enough of an increase
to push seas to 10 feet for the central waters for a time as well.
As such...have extended the Small Craft Advisory for seas there until 4 am.
Remainder of the previous discussion follows. /Jbonk

High pressure builds over the waters behind this
dissipating front on Tuesday. This in addition to a thermal low
developing along the northern California and southern Oregon coast
brings back gusty northerly winds to 20 to 25 knots Tuesday evening
and Wednesday evening. Seas stay up around 7 to 9 feet but could
become steep with more wind driven seas during the evening hours
Tuesday and Wednesday. Summer-like pattern breaks down on Thursday
with the approach of our next frontal system forecast to move
through the waters over the weekend. Winds become southerly
Thursday or Thursday night but should stay below 20 knots until early
Saturday when the front moves closer to our waters. Seas may fall
back down to 4 to 6 feet Thursday into Friday...before winds start
to build seas back up over the weekend. -McCoy


Pqr watches/warnings/advisories...
Pz...Small Craft Advisory for hazardous seas until 5 am PDT Tuesday
for coastal waters from Cape Shoalwater Washington to Cascade Head or
out 60 nm.

Small Craft Advisory for hazardous seas until 4 am PDT Tuesday
for coastal waters from Cascade Head or to Florence or out 60

Small Craft Advisory for rough Columbia River bar until 9 am
PDT Tuesday.



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This discussion is for northwest Oregon and southwest Washington
from the Cascade crest to 60 nautical miles offshore. The area is
commonly referred to as the forecast area.

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