Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 151135
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
333 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...Next front is approaching the
region. Now looks like the front will push to the coast by late
morning, and across the interior this afternoon. Light rain will
develop along the coast between 5 and 7 am, and spread inland through
late morning. Main period of rain likely to be about 3 to 6 hours
long, then will decrease or end.

Now, there is a twist in the forecast. With light gradients, will not
see much in the way of wind this morning. Even though there is plenty
of warm air aloft, there are still plenty of spots in the valleys
through from the Coast Range to the Cascades where temperatures are
in the upper 20s to 32 deg. Still think that will see lowland
temperatures warm as thick lower clouds and rain arrive. But, when
the rain starts, there is some chance that could see few pockets of
freezing rain. Have put a slight chance in the forecast to cover
this possibility. But, even though there is this chance, does appear
that the precipitation will be quite light, so any potential for ice
accumulation looks rather low. Any potential for patchy freezing
rain appears to be in the valleys of the Willapas and North Oregon
Coast Range, and from the South Washington Cascades valleys to the
Upper Hood River Valley. Will also put out a special weather
statement for this morning. Once rain starts, temperatures will
moderate, climbing above freezing quickly. So, any this threat will
be short-lived.

Models continue to indicated low levels will moderate this afternoon,
so expecting just rain for all areas, aside from higher peaks of the
Cascades where will see light snow. Once the front pushes across the
region, will see snow levels drop from 8000 feet this morning down to
around 2500 feet tonight. But showers will be decreasing tonight. So,
looks likely 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 sagging 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.        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...High clouds moving across the area obscuring lower
clouds from satellite view. However with little change from
yesterday the Hood River area still under overcast skies with
MVFR cigs around 2000 ft. Cool, nearly saturated air mass in the
interior valley may be bringing some patchy freezing fog early
this morning. Cloud bases start to lower with the approach of a
cold front this morning. Looks like there will be about 4-6 hours
of -RA and MVFR to all TAF sites; starting in KAST after 15z
then spreading south and east with the front as the day
progresses. Front should exit the area by 00Z with improving
conditions. Brief freezing rain is possible in deeper, wind
sheltered valleys of the coast range that have cooled below
freezing overnight. This front will finally bring an end to the
strong E winds through the Columbia Gorge as our general flow
pattern turns more onshore.

PDX AND APPROACHES...VFR with decreasing E-SE wind this morning.
Cold front will bring lowering cigs, with -RA and MVFR likely
after 18z Fri. Rain will taper to showers behind the front Fri
afternoon and should see return to VFR after 00z Sat. /mh

&&

.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...Air Stagnation Advisory until 10 AM PST this morning for
     Central Willamette Valley-South Willamette Valley.

WA...None.
PZ...Small Craft Advisory for winds from 7 AM this morning to 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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