Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 170259

Area Forecast Discussion
National Weather Service Portland OR
800 PM PDT Mon Oct 16 2017

.SYNOPSIS...Dry weather tonight before a series of progressively
moister fronts bring a prolonged period of wet weather Tuesday
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...Shortwave seen in water
vapor pictures seen approaching 140w Mon evening, will push a cold
front across the reigon Tue. A surface ridge along the coast was
holding clouds at bay this evening, but as the ridge weakens,
onshore flow will develop along the coast overnight allowing clouds
to begin to spread in over the nw. Over the interior light winds for
much of the night with clear skies suggests some fog redeveloping in
the valleys again late in the night. Increased mixing and clouds
ahead of the cold front though suggest whatever fog does develop,
will not likely last long Tue morning.

Remainder of short term discussion unchanged...A series of storms
will bring a return of rain to the region beginning Tuesday and
lasting through the week. Water Vapor imagery shows an atmospheric
river of moisture extending across the whole Pacific that the storms
will be able to tap into.

The first front is expected on Tuesday with rain reaching the SW
Washington and NW Oregon coast mid morning, and moving inland through
the afternoon. The rain will be mostly confined to the oregon
Cascades Tuesday evening. Besides the coast and cascades, Lane County
will see very little if any train with this system.   The first front
expected on Tuesday will east rainfall with each  Rain totals will be
greatest for the Washington coast, the Willapa Hills and the
Washington Cascades where 0.5 to 0.8 inch is expected.  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 very little rain expected for Lane County. The
rain with this system will have a better potential to be heavy at
times, and rainfall totals will be higher. THe SW Washington coast and
Willapa Hills can expect an additional 0.75 to 1.5 inch of rain from
Wednesday morning through Wednesday evening. THe SW Washington
Cascades can see another 0.75 to 1 inch, with around 0.5 inch for the
Oregon coast range and Cascades and less than 0.2 inch for the
interior valleys. Again, areas in Lane County can expect less than
0.05 inch.

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.  ~TJ

.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

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...High pressure will bring VFR conditions through this
evening before fog tries to reform in the lowest valley
locations later tonight. An incoming front should increase winds
Tuesday morning, which should result in fog lifting a little
faster than this morning, especially across the north. However,
an area of low end VFR and MVFR conditions will spread
southeastward across the area Tuesday as a band of rain moves
across the area.

KPDX AND APPROACHES...High pressure will bring VFR conditions
through this evening. Additional MVFR to LIFR conditions are
possible towards 13-15z Tuesday, but confidence in whether these
restrictions will develop at the terminal is low at this point.


.MARINE...High pressure over the waters today will give way to a
cold front moving southeastward across the waters late tonight
and Tuesday. This will likely spread Small Craft Advisory level
wind gusts of 25 to 30 kt across the northern waters later
tonight and allow seas to climb to near 10 ft Tuesday. However,
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 on Tuesday.

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. 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 upper 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 wind
gusts appear possible during the upcoming weekend as well. /Neuman


PZ...Gale Watch from late Tuesday night through Wednesday evening
     for Coastal Waters from Cape Shoalwater WA to Cascade Head
     OR out 60 nm.

     Small Craft Advisory for winds from 1 AM to 1 PM PDT Tuesday
     for Coastal Waters from Cape Shoalwater WA to Cascade Head
     OR out 60 nm.

     Small Craft Advisory for hazardous seas from 5 AM to 9 PM PDT
     Tuesday for Coastal Waters from Cape Shoalwater WA to
     Cascade Head OR out 60 nm.

     Gale Watch from Wednesday afternoon through Thursday morning
     for Coastal Waters from Cascade Head OR to Florence OR out
     60 nm.


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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. is the U.S. government's official web portal to all federal, state and local government web resources and services.