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fxus66 kpqr 200340 
afdpqr

Area forecast discussion
National Weather Service Portland or
840 PM PDT Thu Oct 19 2017

Synopsis...a very wet cold front was finally moving east of
southwest Washington and northwest Oregon this evening. Behind this
front is the leading edge of a cool upper level trough which will
cause snow levels to lower to near the Cascade passes tonight and
Friday. The snow could be heavy at times in the Cascades. The
Post-frontal showers will linger through Friday, perhaps with a few
thunderstorms. Another strong and wet frontal system is expected to
bring more heavy rain to the forecast area this weekend, as well as
wind, especially along the coast but also locally inland. Drier
weather is likely early next week as a strong ridge of high pressure
builds over the western United States.
&&

Short term...tonight through Sunday...a strong, wet front was moving
east of the Cascades this evening with the persistent locally heavy
rain decreasing. The associated cooler air mass associated with the
parent upper trough was already moving onshore this evening and will
continue to move through southwest Washington and northwest Oregon
the remainder of tonight and Friday. The cooler air is unstable, and
will bring a chance of thunderstorms to the coastal waters, the
coast, and the Coast Range tonight and farther inland on Friday. Snow
levels were already lowering to near pass elevations this evening in
the Cascades as evidenced by web cams at santiam and Willamette
passes, and advisory amounts are expected tonight and Friday. The
greatest amounts, which could exceed a foot, would be at ski resort
elevations, but the passes could get close to or exceed 6 inches as
well.

Precipitation will briefly taper off Friday evening before increasing
later Friday night and Saturday as heavy rain from a strong warm
advection with the next warm front moves in. The models suggest the
heavy rain will initially broadside southwest Washington and
northwest Oregon the second half of Friday night and Saturday, before
impacting mainly the northern areas Saturday night, then sweeping
southward late Saturday night and Sunday as the associated cold front
moves southward through the forecast area.

It is now looking like strong winds will be possible at times along
the coast and over the coastal mountains Saturday night as the warm
front lifts north through the area, continuing at times through
Saturday night until the cold front sweeps through. The valleys could
even see gusts in the 35 mph to possibly even 45 mph range Saturday
and Saturday night as well. If so, this could cause some tree damage
and power disruptions in the valleys.

This weekend system is expected to produce more rainfall across the
area than the one earlier today, and as a result has greater
potential to produce hydrological problems for our forecast areas,
including the burn scar areas. We will be continuing to evaluate the
risk of flooding this weekend but it is looking increasingly likely.
Tolleson

Long term...no changes. Previous discussion follows...
Sunday night through Thursday....models are in agreement, that
shortwave ridging will develop over the Pacific northwest early next week.
This will bring a period of dry weather that will likely be followed,
by a weak trough towards the middle of the week. This will provide
the chance for more rain Tuesday night into Wednesday. Models are
suggesting that another ridge of high pressure could bring a dry
period late next week. Bishop
&&

Aviation...mainly VFR conditions through much of the overnight
hours with rain having turned to showers. Could see some MVFR or
even IFR with any heavier showers. Could see more persistent MVFR
conditions return during the day Friday, but more likely to
remain tempo.

Kpdx and approaches...VFR conditions are expected to dominate
as the air mass turns more showery, but it is likely that there
will be occasional temporary MVFR conditions into Fri associated
with showers. Bowen
&&

Marine...still a mix of southerly and westerly winds across the
waters this evening with a few gusts as high as 25 kt. Winds may
pick back up some Friday morning and early afternoon, so issued a
Small Craft Advisory for winds to cover the waters off the
northern Oregon coast during that time frame.

A frontal system moving into the waters late Fri night and Sat will
bring the threat of gale force winds back by Friday night, so
issued a gale watch. Expectations are for this system to track a
little further south than originally anticipated, meaning the
strongest and more persistent gales are likely across the
southern waters Sat and Sat night.

A long period westerly swell around 20 ft will continue at that
level through most of tonight. The swell is expected to slowly
decrease Friday into Friday night, eventually dropping below 15
ft by around midnight Fri night. Another swell train arrives
from the west Sat night, so expect seas to remain in the 14 to
19 ft range through at least then. High pressure begins to build
over the area early next week for more lesser winds and seas.
&&



Pqr watches/warnings/advisories...
or...Winter Weather Advisory until 5 PM PDT Friday for Cascades in
Lane County-northern Oregon Cascades.

High surf advisory until 10 am PDT Friday for central Oregon
coast-north Oregon coast.

High wind watch from Saturday morning through late Saturday
night for central Coast Range of western Oregon-central
Oregon coast-Coast Range of northwest Oregon-north Oregon
coast.

Washington...Winter Weather Advisory until 5 PM PDT Friday for South
Washington Cascades.

High surf advisory until 10 am PDT Friday for South Washington
coast.

High wind watch from Saturday morning through late Saturday
night for South Washington coast-Willapa Hills.

Pz...gale watch from Friday evening through late Saturday night 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-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.

Small Craft Advisory for winds from 6 am to 2 PM PDT Friday for
coastal waters from Cape Shoalwater Washington to Cascade Head or
out 10 nm-waters from Cape Shoalwater Washington to Cascade Head
or from 10 to 60 nm.

Small Craft Advisory for hazardous seas until 11 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-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.

Small Craft Advisory for winds until 1 PM PDT Friday for
coastal waters from Cascade Head to Florence or out 10 nm-
waters from Cascade Head to Florence or from 10 to 60 nm.

Small Craft Advisory for rough Columbia River bar until 6 PM
PDT Friday.

&&

$$

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