Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 172149
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
249 PM PDT Tue Oct 17 2017

.SYNOPSIS...A series of progressively moister fronts bring a
prolonged period of wet weather through next weekend. Breezy
conditions are expected Wednesday and Thursday as well as periods of
heavy rain. Snow levels will lower to near the Cascade passes Friday
and Saturday. Another front may continue rain early next week, but
building pressure aloft may keep this system to the north.

&&

.SHORT TERM...Today through Friday...Light rain with a cold front
moving across SW Washington and extreme NW Oregon will be confined to
the south Washington and north oregon Cascades this evening. The
front should move east of the Cascades tonight and the rain will end.
Satellite imagery suggests that there will be clearing behind the
front. Clear skies, light winds, and lingering surface moisture will
likely lead to fog in some of the interior valleys. High clouds
moving in over the area ahead of an approaching warm front may inhibit
fog development to the north, but areas south of Salem have a good
chance of seeing valley fog Wednesday morning.

The warm front will begin to spread rain Wednesday morning to
northern and coastal areas, and move inland throughout the day. The
rain will mostly stay to the north, and do not expect much if any
rain south of Salem (except for the coast). This front will have a
better tap into the subtropical moisture that extends across the
north Pacific to SE Asia. Modeled precipitable water values are
initializing well with satellite estimations and forecast 1.10 inches
at KSLE (Salem airport) Wednesday morning. This is way above the
October daily average of 0.7 inch.

The high amount of available moisture provides greater confidence
that the rain will be heavy at times. The highest rainfall totals
will be for the Willapa Hills, extreme SW Washington coast, and the
SW Washington Cascades where 0.75 to 1.25 inch of rain is possible
Wednesday morning through Wednesday afternoon. The north Oregon
Cascades and rest of SW Washington may see 0.20 to 0.40 inch of rain
with less than 0.015 between the Columbia River and Salem.

Besides the rain, this front will also increase winds along the coast
Wednesday morning through afternoon. Models are looking more
favorable that the beaches and headlands could have gusts close to 60
mph, so have issued a High Wind Watch for the beaches and headlands.
Although these wind speeds are not particularly strong for the coast,
they will be the strongest winds the coast has seen in quite a while.
Any weakened trees or limbs may easily fall if these wind gusts
materialize which could temporarily disrupt travel or power. Gusty
winds are expected inland as well with gusts up to 30 mph for the
Willamette Valley.

The trailing cold front will move across the area Wednesday night and
Thursday for widespread rain. Rainfall totals will be higher with
this front. An additional 1 to 3 inches of rain is possible for the
higher terrain of SW Washington and north Oregon Wednesday night
through Thursday evening. Other areas (including Lane County) can
expect 0.75 to 1.5 inch of rain. The cold front will also bring a
period of gusty winds to the region. The winds will not be as strong
as Wednesday but will become noticeable in most areas.

AN upper trough continues showers Thursday night and Friday. These
showers will be more unstable with the possibility for thunderstorms
near the coast. Snow levels will lower to near the Cascade passes
Thursday night and Friday morning. The higher Cascades could see 4 to
8 inches of new snow with these showers Thursday night through Friday
afternoon. Localized spots near the passes could see 1 to 3 inches of
snow. ~TJ

.LONG TERM...Friday night through Tuesday....Snow levels will start
to rise as Saturday approaches. A frontal system will start to pass
through the region on Saturday, which has the potential to bring
significant rain into the area. Expect gusty winds especially along
the coast and in the higher terrain of the Coast Range through
Saturday. A new frontal system might continue to bring rain and
showers into the area as we enter early next week.

Timing and location of the heaviest rainfall may continue to change
with future updates, the key message is that a rather wet weather
system may bring abundant rainfall to the area. Expect to see some
rises on area rivers, especially in the coastal basins, and if the
heavy rain sets up over urban areas, some localized urban flooding
issues could develop. Also, locations with significant burn scars
should be aware of possible land or mud slides. Bishop
&&

.AVIATION...A weakening front is dropping southeastward across
the area this afternoon and is producing a mix of MVFR and IFR
conditions as it passes over taf sites. Behind this front, skies
should clear and winds should decrease somewhat so that
additional fog and low clouds could produce additional IFR and
MVFR conditions overnight. In addition, a warm front lifting
northeastward across our northern sites Wednesday morning may
produce additional IFR and MVFR conditions as light rain spreads
into the area, particularly at KAST.

KPDX AND APPROACHES...A mix of IFR and MVFR conditions will
likely impact the site for a couple more hours before clearer
skies arriving from the northwest return VFR conditions to the
terminal. The resulting break in the clouds may allow fog and
low clouds to redevelop overnight. A warm front will likely
spread light rain into the area Wednesday morning. /Neuman

&&

.MARINE...A warm front will lift northeastward across the
northern waters Wednesday morning. This should spread Gale Force
southerly wind gusts of 35 to 40 kt into the northern waters
Wednesday morning before gradually filling in across the central
Oregon waters late Wednesday. A trailing cold front will then
drop southeastward and bring an end to the Gale Force winds
late Wednesday across the northern waters and towards daybreak on
Thursday across the central Oregon waters. In addition, coastal
jet development will likely produce locally stronger wind gusts
of 45 kt within 10 nm of the coast. Either way, the strong winds
should allow seas to climb into at least the mid teens across the
waters late Wednesday.

Winds will likely drop into low end Small Craft Advisory criteria
behind the front, which should allow seas to drop into the low
teens early Thursday. However, this decrease in the seas will
likely be short lived as a large westerly swell of 20 to 22 ft
appears increasingly likely to impact the waters beginning midday
Thursday. High Surf Advisories will likely be needed. An
additional storm system capable of producing at least Gale Force
wind gusts appears on track for either late Friday or Saturday
as well. /Neuman

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Watch from Wednesday afternoon through Wednesday
     evening for North Oregon Coast.

WA...High Wind Watch from Wednesday afternoon through Wednesday
     evening for South Washington Coast.

PZ...Gale Warning from 5 AM to 11 PM PDT Wednesday for Coastal
     Waters from Cape Shoalwater WA to Cascade Head OR out 60
     nm.

     Small Craft Advisory for hazardous seas until 9 PM PDT this
     evening for Coastal Waters from Cape Shoalwater WA to
     Cascade Head OR out 60 nm.

     Gale Warning from 2 PM Wednesday to 9 AM PDT Thursday for
     Coastal Waters from Cascade Head OR to Florence OR out 60
     nm.

     Small Craft Advisory for Rough Columbia River Bar until 6 PM
     PDT this evening.

     Small Craft Advisory for Rough Columbia River Bar from 1 AM to
     6 AM PDT Wednesday.

     Small Craft Advisory for Rough Columbia River Bar from 2 PM
     Wednesday to 3 AM PDT Thursday.

&&
$$

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



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