Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 180427 CCA

Area Forecast Discussion
National Weather Service Portland OR
827 PM PST Sat Nov 17 2018

.Updated aviation section.

.SYNOPSIS...Dry weather with mild days and cool nights will continue
into early next week as high pressure east of the Cascades brings an
offshore flow. The wetter pattern takes over Tue night and Wed as a
couple of systems coming in off the Pacific bring increasing chances
for rain late in the week along with lowering snow levels.


.SHORT TERM...Tonight through Tuesday...Models set on bringing a dry
offshore flow through Tue as the ridge of high pressure just
offshore moves slowly east across the region. Surface high pressure
over the upper Columbia basin is expected to sink south, maintaining
a moderately strong offshore flow, with pdx-dls pressure gradients
on the order of -8 mb. This is expected to remain a little weaker
than the offshore flow earlier this week, and remains capped by a
subsidence inversion that lingers below 2K ft, which should
restrict winds primarily to the gorge and east Portland metro area.

Drying with the offshore flow will tend to limit fog potential next
few nights and mornings despite mostly clear skies and, away from
the gorge, light winds. Expect however to see at least some stratus
develop in the central Gorge and up into the Hood River Valley.
Temperatures will see a limited diurnal swing in the windy spots,
but expect to see continued cool nighttime temps and mild daytime
temps elsewhere.

.LONG TERM...Tuesday night through Saturday...As the upper ridge is
expected to continue to shift east Tue night and Wed, with models
indicator a weakening weather system approaching the coast. In
general, models suggest some splitting of the system as it slowly
approaches, but relatively deep moisture for increasing pops Tue
night and Wed. Similar to a system earlier this week, cannot rule
out a low probability of some light freezing rain in the central
Gorge and Hood River Valley Wed morning as moisture begins to
overrun the cooler low level air trapped under the inversion. A
considerably stronger system potentially arrives Thu or Thu night.
Timing and strength of the system are called into question however
as models begin to show increasing variance in solutions. As of the
12Z runs, all models look promising for rain Thu or Thu night, with
the possibility for strong winds along the coast when the cold front
arrives. After post frontal showers Thu night and Fri, models
diverge sharply in key features Sat with EC at one extreme showing a
ridge returning to the coast, and GFS at the other with a deep
trough approaching the coast. A good case for blending model pops
with some climatology.


.AVIATION...Dry and gusty offshore flow will keep widespread VFR
conditions in place across SW Washington and NW Oregon through
Sunday. The only possible exception would be in the southern
Willamette Valley, which is somewhat sheltered from the offshore
flow. There is a slight chance of some patchy fog or low stratus
around KEUG, but dewpoints have come down quite a bit today and
confidence is fairly high that skies will remain clear overnight.
The offshore flow will continue to produce gusts 35-45 kt at the
west end of the Columbia Gorge.

PDX AND APPROACHES...Dry offshore flow to keep VFR conditions in
place through Sunday. Expect gusts to 25 kt at the terminal
through tonight, with winds gradually decreasing during the day
Sunday. Winds will be stronger east toward the gorge, where gusts
30 to 35 kt should continue through Sunday night. Pyle


.MARINE...Have extended the small craft advisory for wind in the
northern waters through 12Z Sun. The primary wind-prone regions
will be adjacent to the coastal gaps, but widespread gusts to 25
kt will occur as the offshore flow remains more of a larger-scale
event. Wind speeds slowly diminish Sun as the offshore pattern
weakens over the waters. Things begin to get interesting
beginning Wed night as the pattern becomes more progressive. A
strong low looks to take shape in the NE Pac 12Z Thu. The GFS has
been hinting at this feature for the past several runs. The
latest ECMWF has finally caught up to the GFS. Both operational
models spin up a 970-975 mb low center near Vancouver Island 00Z
Fri. Ramped up the wind speeds Thu and Thu night, but still want
remain cautious. Have indicated solid gales Thu afternoon through
Fri morning, but storm force not out of the question should model
trends continue. Conditions settle down Fri night and Sat, but
the 12Z operational model runs have a rather large disparity by

Seas to hover at 5 to 7 ft through Sun morning, then 4 to 5 ft
by Sun afternoon. Seas become more wind driven through early next

Longer range forecast guidance suggests the potential for 20 ft
or greater seas Thu through Fri. The ECMWF wave model shows a 33
ft core near buoy 46089 Thu night, with 20-25 ft seas moving into
the waters. the ENP model is not so aggressive, about 10 ft lower
with the max. Have gone rather conservative for now, generally
15-18 ft, but wave heights will likely need a boost if model
trends hold. Weishaar


PZ...Small Craft Advisory for winds until 4 AM PST Sunday for
     Coastal Waters from Cape Shoalwater WA to Cascade Head OR
     out 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 forecast area. is the U.S. government's official web portal to all federal, state and local government web resources and services.