Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 202124
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
222 PM PDT Fri Oct 20 2017

.SYNOPSIS...Wet October weather continues. Showers ease this evening.
But rain spreads across the region later tonight and continues on Sat
as a warm front lifts across the region. Will be breezy as well for
Sat afternoon into Sat night. Brief let up in the rain towards Sat
evening, but as cold front arrives Sat night, rain will increase
again. Showers on Sunday as the front drops south of the region.
High pressure builds over the region early next week, with dry
weather on tap that very well may last for the week.

&&

.SHORT TERM...Tonight through Sunday...Still have scattered showers
across the region, but the showers are decreasing as main upper
trough continues to shift inland. While not out of question, could
have an isolated thunderstorm through late this afternoon. But think
that thread ends quickly around sunset. Even though snow levels are
around 3500 feet, not seeing much in way of snow accumulation over
the Cascades. Generally, only a few inches have fallen. So, have
ended winter weather advisory for the Cascades.

Next weather action continues to be focused on the atmospheric river
event that has been feeding a rather vigorous weather system to our
west. This system will bring a warm front up against the coast later
tonight, and swing the warm front north across the region on Sat.
Models seem reasonably aligned with steady rain spreading inland
later tonight. Rather favorable overrunning pattern, and with heavier
precipitable water indicating rather moist air aloft, should see
moderate to occasionally heavy rain develop over the Coast mountains
Sat am, and spread inland during the day. Generally, looks like 2 to
4 inches of rain for the coastal mountains north and east into the
south Washington Cascades for Sat, with 1 to 2 inches for the
interior lowlands. Have trended forecasts in this direction.

At this time, seems like warm front will buckle inland and northward
by mid to late afternoon. If this happens, the heavier rain will
shift north as well, but still plenty of rain over much of southwest
Washington. But, likely to get a period of somewhat dry weather for
areas to south of Salem.

Rather impressive winds gradients once the warm front shifts inland.
Will upgrade to High Wind Warning for the Oregon coast, and Coast
Range. Gusts in those areas of 55 to 65 mph not out of the question
for Sat into Sat night. But, gradients not all that favorable was
move farther northward, so will drop keep Willapa Hills/South Wash
coast out of any warning/watch. Winds will subside once cold front
sags southward Sat night. Also, interior lowlands will see gusty
southerly winds by Sat afternoon, with gusts 30 to 45 mph through the
Clark County, Willamette Valley, and nearby areas. So, will issue
Wind Advisory for that area for Sat afternoon/evening.

But, 12Z/18Z models now indicating that the cold front will not be
too far offshore Sat evening, and will start sagging southeastward
towards the region Sat night. Will see rain, heavy at times, spread
out of southwest Washington back into northwest Oregon later Sat
evening. But appears the cold front is moving southeastward across
the region bit faster than earlier models. With this in mind, will
see heavier rain come to an end early Sun am, with transition to
showers on Sunday.

With the anticipated rainfall, have issued a flood watch for parts of
the region. Again, main concern will be rivers draining the Willapa
Hills and the northern Coast Range, but could also be issue on small
streams inland. Also, will likely have ponding of water in low lying
areas, with some urban and small stream flooding on Sat through Sat
night.. Additionally, rainfall rates appear likely to reach values of
concern for our burn scar areas; especially the Eagle Creek burn
scar.

Overall, rainfall totals this weekend look to range from 5 to 8
inches in the Cascades, Coast Range, and Willapa Hills north of
Highway 20. Coastal areas will likely be in the 3 to 6 inch range,
while 2 to 3 inches appear likely for the inland valleys. Areas to
the far south, such as Lane County, will spend the least time
under the aim of this atmospheric river, so about rainfall not as
impressive for that area, with half of said values.   Rockey.

.LONG TERM...Sunday night through Thursday....Models are in
agreement, that shortwave ridging will develop over the Pacific NW
early next week. This will bring a period of dry weather. But, likely
to see considerable low clouds and fog Mon am and again Tue am. But,
should be very great fall weather, with dry and mild conditions for
most areas.  Weak system will pass to our north later Tue night and
Wed, but will only put a small chance of showers for the region.
Afterwards, models agree that will get back into classic October
offshore flow, with mild days and cool nights.Rockey.

&&

.AVIATION...VFR prevailing in a showery weather pattern through 03z
this evening, although there will be scattered MVFR to high end IFR
conditions associated with showers. A slight chance for
thunderstorms remains over inland areas through about 00z. Mainly
VFR conditions early tonight, but cigs will lower across the area
late tonight, likely dropping into MVFR category after 06z along the
coast, and between 12z and 15z at inland TAF sites. Strong southerly
winds will also develop along much of the Oregon coast after 12z,
with breezy conditions in the interior after 15z.

KPDX AND APPROACHES...Mainly VFR conditions tonight as showers
dwindle, but there remains a chance for temporary MVFR conditions
with showers through about 03z this evening. Cigs lowering ahead of
a warm front late tonight and into Sat, likely dropping into MVFR
category by about 15z as heavier rains spread in along with gusty
south winds.

&&

.MARINE...Showers still producing some local gusts to 25 kt this
afternoon over the waters, and with winds eventually picking up
again later tonight with the approach of a warm front from the west,
will extend the small craft advisories past midnight. Wind gusts
eventually expected to reach gale force late tonight into early Sat
as the warm front moves through. Winds may temporarily subside
midday Sat behind the warm front, but as a cold front drops se
through the waters Sat night, winds will return to gale force late
Sat and Sat night. The westerly swell has dropped down into mid
teens range this afternoon, but expected to drop only slowly through
the evening. Seas will become more dominated by the local wind
driven waves late tonight once the gales return, which will tend to
keep wave heights in the 14 to 19 ft range Sat and Sat night.

Sun and Mon will see improving conditions on the coastal waters as
high pres moves across the area.

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Flood Watch from Saturday afternoon through late Sunday night
     for Central Columbia River Gorge-Central Willamette Valley-
     Coast Range of Northwest Oregon-Greater Portland Metro
     Area-Lower Columbia-North Oregon Coast-Northern Oregon
     Cascade Foothills-Northern Oregon Cascades-Western
     Columbia River Gorge.

     Wind Advisory from noon Saturday to midnight PDT Saturday
     night for Central Willamette Valley-Greater Portland Metro
     Area-South Willamette Valley.

     High Wind Warning from 8 AM Saturday to 5 AM PDT Sunday for
     Central Oregon Coast.

     High Surf Advisory until 2 PM PDT this afternoon for Central
     Oregon Coast.

     High Wind Warning from noon Saturday to 5 AM PDT Sunday for
     Central Coast Range of Western Oregon-Coast Range of
     Northwest Oregon.

     High Wind Warning from noon Saturday to midnight PDT Saturday
     night for North Oregon Coast.

WA...Flood Watch from Saturday afternoon through late Sunday night
     for Central Columbia River Gorge-Greater Vancouver Area-I-
     5 Corridor in Cowlitz County-South Washington Cascade
     Foothills-South Washington Cascades-South Washington Coast-
     Western Columbia River Gorge-Willapa Hills.

     Wind Advisory from noon Saturday to midnight PDT Saturday
     night for Greater Vancouver Area.

PZ...Small Craft Advisory for winds and seas until 2 AM PDT
     Saturday for Coastal waters from Cape Shoalwater WA to
     Florence OR out 60 NM.

     Gale Warning from 2 AM Saturday to 5 AM PDT Sunday for Coastal
     waters from Cape Shoalwater WA to Florence OR out 60 NM.

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

&&
&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 5 PM PDT this afternoon for
     Cascades in Lane County-Northern Oregon Cascades.

     High Surf Advisory until 10 AM PDT this morning 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.

WA...Winter Weather Advisory until 5 PM PDT this afternoon for South
     Washington Cascades.

     High Surf Advisory until 10 AM PDT this morning for South
     Washington Coast.

     High Wind Watch from Saturday morning through late Saturday
     night for South Washington Coast-Willapa Hills.

PZ...Small Craft Advisory for winds until 4 PM PDT this afternoon
     for Coastal waters from Cape Shoalwater WA to Cascade Head
     OR out 10 NM-Coastal waters from Cascade Head to Florence
     OR out 10 NM-Waters from Cape Shoalwater WA to Cascade
     Head OR from 10 to 60 NM-Waters from Cascade Head to
     Florence OR from 10 to 60 NM.

     Gale Warning from 2 AM Saturday to 5 AM PDT Sunday for Coastal
     waters from Cape Shoalwater WA to Cascade Head OR out 10
     NM-Coastal waters from Cascade Head to Florence OR out 10
     NM-Waters from Cape Shoalwater WA 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 hazardous seas until 2 AM PDT Saturday
     for Coastal waters from Cape Shoalwater WA to Cascade Head
     OR out 10 NM-Coastal waters from Cascade Head to Florence
     OR out 10 NM-Waters from Cape Shoalwater WA 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 Rough Columbia River Bar until 6 AM
     PDT Saturday.

&&


$$

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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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