Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 110456 AAB
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
855 PM PST Mon Dec 10 2018

Aviation and Marine sections updated.

.SYNOPSIS...A warmer and wetter frontal system will bring additional
rain and mountain snow tomorrow and tomorrow night. The next front
stalls over Washington Wednesday and Thursday keeping portions of NW
Oregon dry. SW Washington may see steady light rain with this
stationary front. The front will finally move inland and across the
region Friday or Friday night. Wet weather is expected to continue
for the weekend and into next week.

&&

.SHORT TERM...Tonight through Thursday...Update early this evening to
add some dense fog for inland areas before the rain arrives later
tonight. Airports at Hillsboro, Aurora, McMinnville, and Salem are
already reporting 1/4 mile visibility. Looks like dense fog will
mostly be limited to areas from the Central Willamette Valley north
in locations with light winds. Airport at Tillamook is also reporting
dense fog, but think it won`t last long rain will approach earlier
there than inland. Also updated PoPs some for the overnight period,
increasing them near the coast and limited the mentionable PoP
coverage all the way inland until closer to sunrise. The previous
short term discussion follows. Bowen

Post-frontal showers have continued today in response to a cool upper
level trough moving through the region. The trough axis is now east
of the Cascades and showers are dwindling and becoming increasingly
confined to the mountains. The shower activity should drop off
completely by early this evening. The trough passage has finally put
an end to the prolonged period of east winds that has been occurring
in the Columbia River Gorge through the past week. The KTTD-KDLS
gradient has now gone slightly positive, and temperatures in the
central Gorge and Upper Hood River Valley are warming up above
freezing again. This should put an end to the threat for wintry
precipitation in this area for a while. Also, it is beginning to look
like the fog and low clouds over much of the lowlands will not
improve much through the rest of today. In areas where improvement
does occur, expect the fog or low stratus will settle back in early
this evening.

This past frontal system was the beginning of a period of a much more
active weather pattern that appears likely to continue at least
through the first half of next week. The next front can be seen on
satellite imagery rapidly approaching the Pac NW today. Associated
high clouds will spread onshore this evening. Then the leading warm
front will begin to spread light rain onto the coast by midnight. The
rain will gradually spread inland through the overnight hours and
into Tue morning. Precipitation will begin as snow in the Cascades
down to 3500-4000 feet, and several inches are expected at the higher
passes through the morning hours. However, the warm front will move
onshore by late morning, lifting snow levels up well above the passes
through the remainder of the day. It will be a wet day across the
entire CWA. However, once we get into the warm sector of the storm by
mid-morning, the models are showing a strong flow out of the west,
around 50 kt at 850 mb. This should mean that the higher terrain
bears the brunt of the precipitation, with rather modest amounts for
the interior lowlands. Model integrated vapor transport values are in
the moderate range, and expect some locations in the higher terrain
of the Willapa Hills, Oregon Coast Range, and the Cascade foothills
will see rainfall amounts of 2-3 inches, with some locally higher
amounts possible. At this time, no significant hydrologic concerns
are expected. The strong winds with the warm front will also likely
result some gusty winds at the coast Tue morning. Gusts were bumped
up to 45-50 mph for the coastal beaches and headlands with the
afternoon fcst update.

The trailing cold front will move onshore and rapidly through the CWA
tomorrow evening. Snow levels will drop quickly below the Cascades
passes behind the front. Solid westerly orographic flow later
tomorrow night into early Wed will probably result in snowfall
accumulations near advisory criteria for all of the Cascades zones.
Showers will drop off steadily through the day Wed as orographics
decrease and upper level heights build over the region. Expect most
of the region will remain dry during the daylight hours.

The next front approaches on Wed night and Thu. There may be some
light warm frontal rain across the northern half of the CWA Thu, but
the latest fcst models are keeping the bulk of the precipitation to
our north. The southern half of the CWA may end up mostly dry Wed
night and Thu. We will be on the mild, southerly flow of this system,
which may allow temps up into the 50s on Thu for much of the region.
Pyle

.LONG TERM...Thursday night through Monday...The active weather
pattern will continue well into next week with a series of fronts
moving across the region. Another front will sweep across the region
on Friday. Snow levels will be near pass levels on Friday bringing
additional snow to the Cascades, just in time for the weekend. This
system will also bring some well needed rainfall to the coast and
valley.

There is some uncertainty in the timing of frontal systems over the
weekend and into next week. At this point in time it looks like
there will be a relative break between systems early Saturday, then
another front moves through late Saturday night and Sunday. Yet
another system arrives sometime Monday into Tuesday bringing more
valley rain and high elevation snow. /tw
&&

.AVIATION...Stable and moist air mass remains over the region
this evening. Do have widespread IFR fog and low stratus inland.
Otherwise, increasing mid and high clouds overnight as next
front approaches. Will see only slight improvement inland but
still widespread IFR to low end MVFR, primarily as fog thins and
lifts to stratus. Warm front will be approaching, with rain
increasing along the coast between 05Z and 08Z, and then
spreading gradually inland overnight. Warm front timing to coast
around 15Z, then to Cascades by 18Z. Conditions will improve to
MVFR behind the front, along with uptick of southerly winds.

PDX AND APPROACHES...IFR through this evening, through with
somewhat drier air out of the Gorge on east winds, should see
conditions lift to MVFR by 08Z. Not much change overnight into
Tue am, as will maintain rather persistent MVFR clouds, with
light rain after 09Z or 10Z. Warm front passes across PDX
between 16Z and 18Z Tue, with flip to southerly winds, but MVFR
conditions will persist, with cigs 2000 to 3000 ft. /Rockey.
&&

.MARINE...No big changes. Warm front will pushing across the
coastal waters late tonight, and onshore early Tue am. Models in
decent agreement, with increasing gusty south winds behind the
front. Generally, will see gusts in 30 to 40 kt range. Have
extended Gale warning to cover all waters, first over the outer
waters later this evening, then inner waters later tonight. Winds
will stay up well through Tue, then ease back late Tue afternoon
into Tue evening as cold front swings onshore. Another round of
stronger winds likely arrives in the waters on Friday. Seas look
to build into the mid-teens on Tue.

Another front will arrive later Wed night into Thu, but winds not
as potent as front on Tue. However, a rather strong front looks
to arrive on Fri, with solid southerly gales, possibly even
knocking at storm force winds in spots.

Seas persist in 14 to 17 ft range Tue night through Wed night.
Then some question, as the models show building seas to close the
week. With all winds expected over the northeast Pac for Thu
through Sun, seems reasonable to expect gradually larger swell
arriving to our region. There is a chance at least one or two
rounds of 20 to 25 ft seas for Thu through early next week. Will
trend in that direction, but if models continue trends, could see
seas even higher.                                    Rockey.

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Dense Fog Advisory until 4 AM Tuesday for...
           All of the Willamette Valley
           Lower Columbia.

WA...Dense Fog Advisory until 4 AM Tuesday for...
           Clark County, including Greater Vancouver Area
           I-5 Corridor in Cowlitz County.

PZ...Gale Warning until 4 PM PST Tue for Outer Waters from
           Cape Shoalwater to Florence, from 10 to 60 NM.

     Gale Warning from 4 AM to 4 PM Tue for Nearshore Coastal
           Waters from Cape Shoalwater to Florence, out 10 NM.

     Small Craft Advisory for Rough Columbia River Bar until 1 PM
     PST Tuesday.

&&

$$

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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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