Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 242246

Area Forecast Discussion
National Weather Service Portland Oregon
245 PM PST Tue Jan 24 2017

.SYNOPSIS...High pres over the region will maintain quiet weather for
next 5 to 6 days, with seasonal temperatures with generally light
winds. A weak upper level shortwave will move through later today and
tonight. This will bring increasing clouds and possibly some light
showers and snow showers to the Washington and far NW Oregon
Cascades. A decaying front arrives late Wed into Thu, bringing a
threat for some very light rainfall. An upper level ridge then
arrives to keep dry weather in place late Thu through Sat. Another
weakening front arrives Sun, bringing more chances for light rain.
Temps remain seasonal through the next week.


.SHORT TERM...Tonight through Friday...A ridge of high pres over the
NE Pac is slowly nosing toward the Pac NW today. The low level
stratus deck that formed from the PDX metro area up through the I-5
corridor in SW Washington has been slow to clear, and it appears it
may remain through the day from around Scappoose up through Kelso. A
weak shortwave trough is riding down the northerly flow out ahead of
the upper ridge and is bringing increasing mid and high level clouds
across the region this afternoon. Mosaic radar imagery shows some
weak echoes forming on the west side of the Washington Cascades over
the past couple of hours. Given that the models have been
consistently putting QPF into our south Washington and far north
Oregon Cascade zones, decided to put a slight chance of showers or
flurries in for this evening and overnight. Think the increased
clouds will keep fog and low clouds even patchier overnight into Wed
morning than they were today.

A frontal boundary now inside of 140W will push onshore later Wed
into early Thu. This front will stretch and shear apart for the most
part before it reaches the coast, but will probably wring out some
light precip as it makes landfall. Will hang onto low end chance PoPs
at the coast and a slight chance inland. However, expect the main
impact will be more clouds and the likely prevention of fog and low
clouds Thu morning.

The upper level ridge will move over the Pac NW later Thu and
strengthen on Fri. This will lead to decreasing clouds Thu afternoon
and evening. Any lingering showers should also end by early Thu
evening. There may again be areas of fog and low clouds over portions
of the interior lowlands Fri morning. But expect most everyone will
have full sun by Fri afternoon. Expect high temps near seasonal
normals. Pyle

.LONG TERM...Friday night through Monday...A sharp upper level ridge
will remain over the region through Sat, keeping dry weather in place
with near seasonal temps. There may be lowland clouds and fog to
start Sat, but the higher terrain will remain clear. The ridge axis
will shift east of the Cascades by Sun, allowing a weakening frontal
boundary to push onto the coast. This system currently looks unlikely
to produce more than some very light rain and increased clouds. The
ridge is modeled to rebuild on Mon, bringing another dry day. Then a
potentially much moister system is modeled to arrive sometime in the
Tue/Wed time frame next week. Pyle


.AVIATION...VFR conditions across most of the this afternoon, with
the fog and low stratus clearing across much of the Portland metro
terminals, but remains along the lower Columbia from KSPB to KKLS.
Meanwhile, increasing mid clouds associated with upper level
disturbance are increasing from NW, presently reaching KAST and
much of the Oregon coast. Expect cigs to remain VFR for a few
hours, before a more solid MVFR deck pushes into the coast.
Somewhat more complicated forecast overnight with several
competing factors. Overall expect fog development to be less
widespread tonight than last, with fog more confined to KKLS
through KHIO and possible also around KEUG. Elsewhere, bkn-ovc
mid-level cloud deck should remain, with cigs lowering to MVFR.

PDX AND APPROACHES...VFR this evening with increasing mid-level
cloud deck arriving. Expect these clouds to eventually lower to
MVFR later tonight and persist through the TAF period. Some
fog/low stratus may initially develop to NW and W of terminal, but
do not expect it to impact terminal early Tuesday morning.  Cullen


.MARINE... Light winds and gradually decaying seas continue across
the coastal waters this afternoon through late Wednesday. A front
that is weakening will move a cross the waters late Wednesday
evening, and while southerly winds will increase ahead of the
front. Do not anticipate gusts much beyond 20 kt, but there does
remain a small chance gusts increase enough to warrant a Small
Craft Advisory, and will allow next shift to further evaluate this.
After this, a stronger front will linger well offshore later in
the week and into the weekend, but should remain far enough
offshore to maintain winds below advisory criteria from Thursday
through the end of the week. A larger and long period westerly
swell will push into the waters later Wednesday, building seas
into the mid-teens. Seas will then hold between 9 and 11 feet
through the rest of the week.Cullen


PZ...Small Craft Advisory for Rough Columbia River Bar until 5 PM
     PST this afternoon and from noon to 5 PM PST Wednesday.



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This discussion is for Northwest Oregon and Southwest Washington
from the Cascade crest to 60 nautical miles offshore. The 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.