Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 152302
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
300 PM 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...Tonight through Monday...As expected, temperatures
warmed across the area this morning as weak southerly low-level flow
developed ahead of the front. This morning`s cold front continues to
advance east across the Cascade foothills and Cascades. A few
continued showers may continue through the rest of the day, but new
precipitation amounts out of these will remain rather minimal, if at
all. Models continue to indicate low to mid level temperatures will
moderate, so expecting just rain 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 with decreasing
coverage of showers tonight, only a few inches of snow can be
expected for the Cascades tonight through early tomorrow.

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 generally north of a Lincoln City to Salem to
Santiam Pass line, with little if any moisture to the south. 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. Little change Monday with
continued zonal flow and the bulk of moisture aimed at western
Washington, mostly to the north of our forecast area.  Cullen

.LONG TERM...Monday night through Friday...We start next week under
relatively flat, zonal flow with a broad ridge off the coast of
California and an approaching trough coming out of the Gulf of
Alaska. We will see our first widespread rain in a while with this
system starting Tuesday morning and continuing through Wednesday
morning, with rainfall amounts around an inch for most of the area.
Snow levels will be falling through this event, starting around 5000-
5500 ft Tuesday morning, and falling to around 1500 ft by Wednesday
morning. Showers will be tapering off midday Wednesday. 1000-500-mb
thicknesses drop down to 523 dam, and 850 temps only lower down to
-4C while precip is falling, indicating no chance for snow down to
the valley floor with this system, though locations in the Cascade
Foothills and Coast Range could see a dusting of snow down to 1500
ft on Wednesday as precip is coming to an end. Good news for skiers
is that with ~1 inch of liquid equivalent, and snow levels starting
around 5500 ft, the resorts could see a foot of snow with this
system.

Beyond Wednesday, ridging builds back up over the eastern
Pacific and along the West Coast. Ensemble members generally agree
on some sort of a ridge over the eastern Pacific, though the exact
positioning is in flux. Most models suggest another dry spell
continuing into the weekend, with the return of east winds.  Only
difference from this last dry spell may be that model temperatures
in the Columbia Basin are looking a little colder, suggesting colder
air filtering into the Willamette Valley as we go into next weekend.
-McCoy

&&

.AVIATION...Cold front has brought MVFR cigs inland as expected,
but precipitation has been lacking. In fact, as of 23Z there are
no ASOS locations reporting precipitation. Expect isolated
sprinkles and showers to continue into the evening, but otherwise
conditions will remain mostly dry. Ceilings are likely at their
worst right now with a gradual increase through the evening to
VFR conditions everywhere overnight.

PDX AND APPROACHES...Current MVFR cigs will improve to VFR this
evening. Isolated sprinkles or light showers are possible through
this evening with dry conditions afterward. /Bentley

&&

.MARINE...Small craft advisory for the outer waters seems
justified with consistent small craft strength winds at Buoy 89
and periodic small craft winds at Buoy 29 and Buoy 50. However,
if any of these winds are reaching the inner waters it is likely
only the outer portions of the inner waters as KAST has seen very
little wind and TMK and ONP post frontal winds haven`t been that
strong. Seas look to remain below 10 feet through this period of
northwesterly fetch, however occasional periods of 7 to 9 seconds
have been showing up on both Buoy 89 and Buoy 29. Will need to
watch these conditions into the evening and see if they continue
and may need a small craft advisory for seas. Marine conditions
remain mostly benign through the remainder of the weekend and
into early next week until a stronger front approaches the coast
Tuesday. Pre-frontal winds will increase to at least small craft
strength with gales likely for most of the waters. In addition
to the gusty winds, seas will also increase into the mid teens
with this front and persist through the middle of next week.
/Bentley

&&

.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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