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Area forecast discussion 
National Weather Service Portland or
936 PM PDT Thursday Oct 8 2015

Synopsis...mild night ahead with passing high clouds will allow
another round of fog to develop overnight. The low that was once oho
has weakened as it neared the Pacific northwest this evening.
However...there will still be an increase in winds and seas for the
coastal waters Friday and Saturday. A weak cold front will spread
light rain to parts of northwest Oregon and SW Washington Friday...followed
by a moister front on Saturday and Saturday night. Showers will
decrease Sunday. Zonal flow expected for next week with occasional
weak fronts.


Update...the upper level wave associated with the former oho has
weakened considerably as the remnants near the Pacific
northwest...however a line of thunderstorms did develop ahead of it
late this afternoon. This line of thunderstorms was way offshore near
130n and should stay offshore as the remnants continue to move

Any clearing of skies tonight should lead to radiation fog as the
surface temperature/dew point depressions are small. There is signs
of fog developing in the interior low lands this evening with 3 miles
visibility reported at scapoose. Satellite suggests further clearing
inland the next few hours. This clearing should allow temperatures to
cool enough for more widespread low land fog developing around
midnight...and persisting through Friday morning.

The surface front expected for Friday is unimpressive on satellite
imagery this evening. Models forecast that the tale end of the front
will swing over northwest Oregon and SW Washington Friday. Abundant moisture
is available with this front...but the dynamics are on the weak side.
The coast...Coast Range...and Washington Cascades have the best
chances for rain...with less than 0.25 inch expected. Only light
rain...less than 0.05 inch is expected for the Willamette Valley and
the Oregon Cascades.

Although rain is not very impressive Friday...south winds along the
coast and higher terrain will be gusty with gusts up to 50 miles per hour.

There is greater confidence in higher accumulation rain on Saturday
as a more organized surface front will move across the region. Tj

Previous short term...tonight through Sunday...low clouds and fog
have dissipated at this hour and will expect some modest clearing
overnight tonight. This and dew points in the 50s should result in
another batch of fog tonight and early tomorrow. Coastal areas will
see more fog and low clouds tonight as well as the ocean stratus
field gets pushed back onshore.

Oho remnants will weaken as they make their closest approach to our
area. The surface low pressure rises to around 986 mb near 138w off
the mouth of the Columbia. The extratropical low then strengthens
again reaching 981 mb by 12z at 55n 138w as they interact with the
broad upper trough over the Gulf of Alaska. The trailing surface
trough will drag close to the coast tomorrow morning and bring wind
gusts of 45-50 miles per hour to the coast. The offshore gradient will also
serve to weaken the incoming front from the advancing upper trough.
There will be plenty of tropical moisture left over the area to
still bring rains to a large part of the area although the central
Cascades may be left dry.

A stronger front with dynamic support form the upper trough will
cross the region Saturday and bring some of the best rains seen in
some time through Saturday night. The associated cold front will
also have tropical moisture from western Pacific typhoon remnants
entrained in the westerly Pacific flow. Upwards of a couple inches
will be possible ending Sunday morning for the Willapa Hills...north
Coast Range...and Montana St helens area extension of the South
Washington Cascades. The associated surface low will also pass north
of our area and allow north-S pressure gradients to open up with and
just behind the cold front crossing midday Saturday through the
early evening. Gusts 50-55 miles per hour at the coast and around 35 miles per hour for
the inland valleys will be likely although briefly higher gusts will
be possible during the frontal passage. Rain is followed by
orographic showers behind the front and continuing into Sunday.

Still have concerns for overall public safety this weekend on the
beaches and jetties as unusual swell combinations will affect our
coast. Please refer to the Special Weather Statement for additional
information. /Jbonk

Long changes. Previous discussion follows...Sunday night
through Thursday...weak upper level ridging will keep most of the
shower activity confided to the northern portions of the forecast
area late Sunday. Models continue to show another front moving across
the Pacific northwest on Monday but are still struggling with some of
the details. As of looks like most of the quantitative precipitation forecast will remain
well to our north...with only modest accumulations expected across northwest
Oregon and SW Washington. Upper level ridging returns Tuesday and
looks to persist through much of the upcoming week. This will bring
the return of warmer and drier weather...with temperatures remaining
a few degrees above normal. /64


Aviation...patchy fog already beginning to form in a few areas as
high dewpoint air mass remains over the Willamette Valley and
southwest Washington. Expect widespread IFR and LIFR fog to
continue to form in many areas after 07z. Fewer high clouds
tonight...with one large hole over the Willamette Valley at 04z
will help cooling and fog formation. Mixing will likely begin
around 12z-14z as surface pressure gradients increase with
approaching extratropical oho low remaining well offshore. Fog and
low stratus should lift to VFR or local MVFR deck after about 18z
with increasing winds and some light rain. Expect coastal areas to
remain mostly VFR except some local LIFR ceilings in fog over the
north coast likely for a few hours 09-12z before winds increase
and mix to a VFR cloud deck sometime around 16z. Schneider

Kpdx and approaches...VFR conditions expected through this evening
with broken high clouds overhead. Light winds and clearing skies
should allow IFR fog or low stratus to form between 07z and 09z.
Approaching front and increasing surface wind likely will mix out
the low clouds between 14z and 18z with some light rain
developing. Schneider


Marine...fairly benign conditions continue through this evening
with southerly winds of 10 to 20 knots and seas remaining at 3 to 5
feet. However seeing the first signs of extratropical remnants of oho
in the 5 feet long period S swell over the coastal waters. The
surface low will pass quite a way to the west of the coastal
waters but the wind field will expand to encompass Oregon and
Washington coastal waters Friday morning. Winds will begin to
increase after midnight 20 to 25 knots then rapidly near sunrise to
25 to 30 knots with gusts 35 to 40 knots gales over the outer waters
and then spreading to the inner waters during the morning. Seas
will also increase with the long period swell being overshadowed
by shorter period...9 second...swell from the southwest generated
closer to our region and seas building to around 12 feet in the
morning and then 15 feet in the afternoon. The strongest winds
will be further offshore.

There will be a relative lull in the winds later Friday and Friday
night...although expect wind speeds will still be at solid Small
Craft Advisory speeds. The trailing cold front will move through
the waters on Sat...and expect another round of gales will
accompany this frontal passage. At the same time old oho swell
will continue arriving...but with longer periods containing more
energy on Saturday. This will result in higher surf and the
strongest surf of the season so far. the present it
doesnt look like there will be enough energy to warrant a high
surf advisory. If thats not enough a west-northwest swell is expected to
arrive Saturday evening. This will result in a period of confused
seas combined with wave heights running in the 13 to 15 feet range.
Please see the marine weather statement /pdxmwspqr/ for additional
information about these concerns. Seas do look to finally subside
during the early part of next week. Schneider


Pqr watches/warnings/advisories...
Pz...Gale Warning from 2 am to 5 PM PDT Friday for waters from Cape
Shoalwater Washington to Cascade Head or from 10 to 60 nm-waters
from Cascade Head to Florence or from 10 to 60 nm.

Gale Warning from 5 am to 5 PM PDT Friday for coastal waters
from Cape Shoalwater Washington to Cascade Head or out 10 nm-
coastal waters from Cascade Head to Florence or out 10 nm.

Small Craft Advisory for rough Columbia River bar from noon to
11 PM PDT Friday.



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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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