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fxus66 kpqr 191703 
afdpqr

Area forecast discussion
National Weather Service Portland or
905 am PST Fri Jan 19 2018

Synopsis...an upper level trough of low pressure will make its way
across the Pacific northwest today and tonight, keeping the region in a
cool and showery air mass. Large waves at the coast will ease later
today with more typical wave heights Saturday. A weak ridge of high
pressure Saturday will temporarily decrease the showers, but then
another system arrives Sunday for more rain and mountain snow. An
active weather pattern continues next week, and it looks like snow
levels will dip down into the lower foothills in the latter half of
the week.

&&

Short term...today through Sunday...showers to continue today and
tonight across the region, as an upper level trough of low pres
moves from near 130w this morning, to east of the Cascades tonight.
Snow levels remaining in the 2k to 3k ft range through tonight, so
should see some accumulations in the Cascades, but not likely to
reach advisory amounts. With showers and low snow levels, still not
out of the question to see some small hail reports lower elevations
today, although with modest warming aloft, convection is not likely
to be as strong as yesterday. Temps in the Hood River Valley and
central gorge were right around freezing this morning with patchy
light rain. Have not seen any indication of icing going on there,
but will stick in a chance for some freezing drizzle this morning
before diurnal warming kicks in. Seas still running in the upper
teens along the coast, but will continue to subside today. Will
allow the high surf advisory to continue for at least a short while.

Remainder of short term discussion unchanged... any lull behind this
system will be brief, as our next low pressure system is already in
the process of crossing the Gulf of Alaska. This system will push
another robust Pacific frontal system toward the pac northwest coast, with
rain spreading onshore by Sunday morning. 12z and 00z European model (ecmwf)
ensembles, 00z uw WRF-GFS, and the 06z NAM all suggest winds will
reach or exceed warning criteria for the coast, though the easterly
component to the pressure gradients will likely keep the stronger
winds confined to the beaches, headlands, and adjacent coastal
waters. Given this good model agreement, we will issue a high wind
watch for the beaches and headlands in all our coastal zones.
This event looks marginal; given latest guidance, 55-65 mph gusts are
most likely for the beaches and headlands. There is still some chance
that a strong Pacific jet develops a secondary low along the front
somewhere along the Oregon or northern California coast. If this
occurs to our south, it could limit the wind potential for our
forecast area.

The frontal system will be in the process of occluding while moving
onshore Sunday morning. This should keep our Cascades from really
getting into this system's warm sector, and precip should fall mainly
as snow for the passes and above. Whether or not an advisory will be
needed for the Cascades largely depends on whether or not the system
splits while moving onshore Sunday. The fast progression of this
front will probably limit snow accumulations, with about 3 to 7
inches expected for most of our Cascades. Valley rain and mountain
snow showers will persist behind the front, with snow levels
generally around 3000 feet. Weagle

Long term...Sunday night through Thursday...by the time the showers
taper off behind sunday's frontal system, the next large upper low
will be taking shape in the Gulf of Alaska. This will serve as the
parent low pressure system next week, guiding several waves of low
pressure toward the pac northwest. Post-frontal showers on Monday will
likely decrease as weak ridging aloft slides across the pac northwest. The
forecast becomes more complicated Tuesday, as an increasing number of
models are involving some southern stream energy with the Gulf of
Alaska upper trough. There are several possible outcomes depending on
how much phasing occurs between the two systems. The models which
show more phasing (such as the 00z ecmwf) develop a stronger surface
low offshore which then curls north into British Columbia. This would
bring a rather typical front through the forecast area, with snow
levels remaining well up into the foothills. Some models and
ensembles show weaker or later phasing, thus a weaker surface low and
a more southern track. If that occurs, snow levels could be
considerably lower as precip moves through on Tuesday. For now, we
favor the 00z European model (ecmwf) solution, considering the strong Pacific jet
stream and baroclinicity available for rapid cyclogenesis. Just about
all models eventually usher in a much cooler air mass by Thursday as
showers continue. The 00z European model (ecmwf) suggestion of -5 to -6 deg c 850 mb
temps would likely result in snow levels dropping down into the lower
foothills, but not quite the Lower Valley floors. Either way, temps
appear likely to swing to below normal by the middle to latter
portion of next week, with continued unsettled weather across the
Pacific northwest. Weagle

&&

Aviation...a more organized shower band moving across the
coastal areas as of 17z. This has produced greater coverage of
MVFR. Elsewhere, a mix of MVFR to VFR, except for areas of IFR in
the central Columbia Gorge and Upper Hood River Valley. Expect a
mix of MVFR and VFR at all taf sites through 12z Sat, with
greater coverage and longer duration MVFR for the coastal sites.
Models show another organized precipitation band moving onshore
this evening.

Pdx and approaches...expect primarily VFR at the terminal and
vicinity through 12z Sat. However, there is a 40 to 50 percent
chance of brief MVFR through this evening. The odds for MVFR
increase slightly after 06z Sat as a surface trough moves across
the area. Weishaar

&&

Marine...a 992 mb low pres center was near buoy 46207 at 17z.
Buoy reports continue to indicate solid Small Craft Advisory wind
speeds with gusts up to 30 kt. This will continue through the
afternoon. Wind speeds ease a little this tonight, likely falling
just under Small Craft Advisory levels late tonight. The next
significant system will move through the waters late Sat night
and Sun morning. The 12z NAM, GFS and the 00z European model (ecmwf) are fairly
similar showing 40-45 kt boundary layer (0-1 km mean wind for the
ecmwf) 06z sun. The GFS indicates a narrow band of 45-55 kt
boundary layer wind 12z sun. The 12z NAM is a little weaker with
its boundary layer wind forecast 12z sun, but still indicates
low-end storm force speeds. This system will be a quick-hitter,
with about 6-9 hrs of storm force potential. Will need to
consider the possibility of a coastal jet with this system.

Wind speeds settle down Sun afternoon into the first part of next
week. There is the possibility additional gales Tue and Wed.

Seas continue to hover near 20 ft this morning, but will ease to
the mid-teens by late afternoon. Seas hold around 15 feet late
tonight through Sat evening, but will build again late Sat night
and Sun morning with the next strong system. There is the
potential for combined seas to peak near 25 ft sun. The dominant
period will be shorter than this last evening, around 12 to 13
seconds, but guidance is suggesting a mixed swell situation. This
will lead to very choppy and rough conditions. Models show a
dynamic fetch is likely. Thus, have gone slightly higher than
the current model forecast. Weishaar

&&

Pqr watches/warnings/advisories...
or...high surf advisory until 3 PM PST this afternoon for central
Oregon coast-north Oregon coast.

High wind watch from Saturday evening through Sunday morning
for central Oregon coast-north Oregon coast.

Washington...high surf advisory until 3 PM PST this afternoon for South
Washington coast.

High wind watch from Saturday evening through Sunday morning
for South Washington coast.

Pz...storm watch from Saturday evening through Sunday morning for
coastal waters from Cape Shoalwater Washington to Florence or out
60 nm.

Small Craft Advisory until 4 PM PST Saturday for coastal waters
from Cape Shoalwater Washington to Florence or out 60 nm.

Small Craft Advisory for rough Columbia River bar until 4 PM
PST Saturday.

&&



$$

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