Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 151743
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
943 AM PST Fri Dec 15 2017

.SYNOPSIS...A front will push across the region this morning, with
rain spreading inland this morning. May see patchy freezing rain in
the the valleys where temperatures may not warm above freezing until
later in the morning, but not much if any ice accumulation is
expected. Active storm track carries main storms into southwest
Canada, with occasional rain over Washington and far nw Oregon for
this weekend into early next week. Will see rather strong front
arrive next Tue and Wed with plenty of rain and mountain snow.
Afterward, it looks to be colder but dry to end next week.

&&

.SHORT TERM...Today through Sunday...The early morning forecast
updates to introduce mention of patchy freezing rain remains on
track. Again, this is expected to be relatively minimal in impact
given both the little moisture amounts and the short time window
before temperatures warm above freezing. A leading line of very light
rain/sprinkles is currently pushing into the Cascade foothills and
may produce some slick spots as temperatures are remaining around 30
degrees. The main line of precipitation will follow later this
morning at the coast and across the interior this afternoon. Still
expect the main period of rain to last 3-6 hours before largely
decreasing. Mid-level clouds continue to thicken and lower across the
region and temperatures also are warming. Nonetheless, there are
still many spots in the valleys from the Coast Range to the Cascades
where temperatures are around 30 degrees. So the threat remains for
very limited freezing rain accumulation on surfaces with initial
rain, generally in the valleys of the Willapa Hills and North Oregon
Coast Range, and from the South Washington Cascades valleys to the
Upper Hood River Valley. Once rain starts, temperatures will climbing
above freezing rather quickly. So, to reiterate, this threat will be
short-lived.

Models continue to indicate low-levels will moderate this afternoon,
so expecting just rain by mid afternoon for all areas aside from
higher peaks of the Cascades, which will see light snow. Once the
front pushes across the region, snow levels drop from 8000 feet this
morning down to around 2500 feet tonight. But showers will be
decreasing tonight. Thus, only a few inches of snow can be expected
for the Cascades tonight.

Active storm track offshore will carry main energy into southwest
Canada. But will see occasional moisture moving southward at times
across western Washington and far northwest Oregon. This will keep
some threat of rain for areas north of a Lincoln City to Salem to
Santiam Pass line, with little if any moisture to the south of that
line. With snow levels 2500 to 4000 feet, and QPF not all that
impressive, only would expect 2 to 4 inches of snow this weekend for
the south Washington and North Oregon Cascades.      Cullen/Rockey.

.LONG TERM...No Changes. Previous discussion follows...Sunday night
through Thursday...Models are in decent agreement the area will be
under zonal flow with the jet stream remaining across southern
British Columbia and far northern Washington Sunday night and Monday.
This will leave our more northern zones open to a period or two of
light rain as a weak front drags southward towards the region, but
rain chances appear considerably less towards Lane County.

Models seem to also be coming into agreement a shortwave trough and
attendant front will drop southeastward out of the Gulf of Alaska
and usher in a good shot of valley rain and mountain snow Tuesday
and Tuesday night. As upper level ridging builds northward into
British Columbia behind this feature late Wednesday and Thursday,
our flow should become increasingly northeasterly. This will in turn
likely lower snow levels to near the valley bottom, but
precipitation will almost certainly have ended by that point. If
precipitation were to linger across the area Wednesday night and
Thursday, our flow will likely not be quite as northeasterly, and as
a result, snow levels will likely be higher.  /Neuman

&&

.AVIATION...Only light east winds remain through the Gorge a a
cold front approaches the coast. This front has started to bring
some light showers and sprinkles inland. A few isolated locations
have reported freezing drizzle, but with light precip amounts and
above freezing ground temperatures, this will be short lived and
should have little to no impact. Ceilings and visibilities have
come in a bit lower at KAST than expected, but expect this to be
short lived as conditions improve dramatically behind the front.

PDX AND APPROACHES...Mostly VFR conditions with a short period of
MVFR cigs possible along and right ahead of the front this
afternoon. Behind the front rain will become more showery and
conditions will return to VFR. /Bentley

&&

.MARINE...High pres offshore briefly interrupted by a cold front
moving through the waters today. The SCA for winds in the outer
waters looks marginal, but most models do show 25 kt winds in
the boundary layer, which indicates some gusts may reach that
high. High pressure moving closer to shore should cause winds to
ease in the evening. Seas will likely remain just below 10 feet
for the most part with this system, though shorter periods may
make it a bit choppy later today into Sat. Latest ENP guidance
shows lighter seas in between fronts later Sat through early Sun,
then another weak frontal system is expected later Sunday. Swell
energy from the Gulf of Alaska will again push seas close to 10
ft behind this front Sun/Mon. A stronger cold front may bring
low-end gales Tue, with seas potentially pushing into the teens.
/mh Weagle

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.

WA...None.

PZ...Small Craft Advisory for winds until 8 PM PST this evening for
     Waters from Cape Shoalwater WA to Florence OR from 10 to
     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 CWA, or forecast area.


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