Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 171030
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
329 AM PDT Tue Oct 17 2017

.SYNOPSIS...A series of progressively moister fronts bring a
prolonged period of wet weather today 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.

&&

.SHORT TERM...Today through Thursday...Surface ridge is holding
longer than previously forecasting, holding precipitation back off
the coast longer than previously thought. We are starting to see the
ridge break down, however, which will allow the precipitation to make
it to the south WA coast in the next 6 hours. Over the rest of the
interior, relatively calm winds and clear skies have allowed for
areas of radiational fog to develop. As the front makes it closer
later this morning, expect fog to mix out ahead of the front.

This system is the first in a series of storms that will bring rain
back to the region through this weekend. Water Vapor imagery shows an
impressive atmospheric river of moisture stretching from SE Asia all
the way to British Columbia. This "river" will be the moisture feed
for these storms, bringing heavy rain at times to the Pacific
Northwest.

This first front on Tuesday will keep the heaviest rain north of our
area. However most locations across our area will see some rain with
the front today. Only exception may be the Lane County Cascades. Rain
totals with this system will be greatest along the Washington Coast,
the Willapa Hills, and the Washington Cascades. Around 0.25
inch of rain is likely for for the north Oregon Cascades and coastal
mountains with less than 0.2 inch expected elsewhere. Only light rain
(less than 0.05 inch) is expected for Lane County.

There will be break in the rain Tuesday night. Some fog may form in
the in the interior valleys and along the coast Tuesday night, but
any sky cover will limit the extent of this fog.

A moist warm front will start the second round of rain for the SW
Washington and NW Oregon coasts Wednesday morning. The extent of the
rain will be similar with this front with the best chance for rain
across the north and little-to-no rain expected for Lane County. The
rain with this system will have a better potential to be heavy at
times in our northern counties, and rainfall totals will be higher.

There will not be a break Wednesday night as the trailing cold front
front moves across the area Wednesday night through Thursday. This
front is looking juicy, and expect widespread rain that will be heavy
at times. An additional 1.5 to 2 inches of rain is expected 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. Depending on the rain rates, there
could be localized flooding concerns Wednesday night and Thursday
with the best chances for hydrologic concerns in the Willapa Hills
and near the fire burn scars in the Columbia River Gorge.

Besides rain, the Wednesday and Thursday fronts will generate windy
conditions for the coast and breezy conditions inland. South gusts
up to 45 mph are possible for the beaches, headlands, and higher
terrain with gusts of 30 to 35 mph possible for the interior valleys
including the Willamette Valley.  ~McCoy

.LONG TERM...Thursday night through Monday....No changes.
Previous discussion follows... Latest model consensus has the warm
front pushing onshore along the Oregon and Southern Washington Coast
late Thursday night. A baroclinic zone moves through the region with
model forecast PW values remaining high, continuing moderate to
heavy rainfall. Expect gusty winds especially along the coast and in
the higher terrain of the Coast Range with this system. Snow levels
will remain rather high around 5,000 feet. The cold front finally
passes across the region by late Friday, with ongoing showers and
lowering snow levels as the colder air mass moves over the Pacific
Northwest.

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...Weak high pressure over the areas giving way to a
front approaching from the northwest. Marine stratus approaching
the coast should be replacing the IFR fog conditions with MVFR
cigs early this morning. Inland areas are a mix of VFR and IFR
due to fog early this morning. Will probably see fog expand some
through 15-16Z, then effects of approaching front should diminish
the fog. Rain develops coast after 15Z with generally MVFR
coastal mountain westward. Inland should have low VFR as the
front crosses. Tail end of front may be far enough north where
KEUG area does not receive any rain. Mtns and Cascades passes
becoming obscured in clouds by 18Z.

KPDX AND APPROACHES...Mix of VFR and IFR in fog through about
16Z. Then increasing clouds and wind with approaching front
should dissipate the fog. Gradually lowering cigs as the front
moves through with low VFR with rain prevailing from 18Z to 23Z
or so./mh

&&

.MARINE...A cold front moves southeastward across the waters
today with Small Craft Advisory wind gusts of 25 to 30 kt across
the northern waters through this morning. Seas will climb to near
10 ft then subside tonight. The front should weaken enough to
prevent these winds and higher seas from spreading into all but
the most northernmost portions of the central Oregon waters.

The next front will drop southeastward across the waters on late
Wednesday and early Thursday and appears likely to spread Gale
Force wind gusts of 35 to 45 kt into the waters so have issued a
Gale Warning for this system. A coastal jet could produce
locally stronger winds within 10nm of the coast. Either way, the
strong winds should allow seas to climb into at least the mid to
teens late Wednesday. After winds drop off behind the front
Wednesday and early Thursday, seas should drop rather quickly
into the low teens. However, models continue to suggest a large
westerly swell around 20 ft will move into the waters late
Thursday and may necessitate a High Surf Advisory. Additional
storm systems capable of producing Gale Force gusts appear
possible during the upcoming weekend as well.  /mh /Neuman

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for winds until 1 PM PDT this afternoon
     for Coastal waters from Cape Shoalwater WA to Cascade Head
     OR out 10 NM-Waters from Cape Shoalwater WA to Cascade
     Head OR from 10 to 60 NM.

     Gale Warning from 5 AM to 11 PM PDT Wednesday for Coastal
     waters from Cape Shoalwater WA to Cascade Head OR out 10
     NM-Waters from Cape Shoalwater WA to Cascade Head OR from
     10 to 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 10 NM-Waters from Cape Shoalwater WA
     to Cascade Head OR from 10 to 60 NM.

     Gale Watch from Wednesday afternoon through Thursday morning
     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 from 8 AM
     this morning to 6 PM PDT this evening.

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

&&

$$

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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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