High Wind and Strong Wind in Oregon, January 5 to 6, 2019

Area Forecast Discussion
National Weather Service Portland OR
200 PM PST Sat Jan 5 2019

.SYNOPSIS...Low pressure off the northern California coast will lift
northward and bring a strong burst of southwest wind to western
Oregon and southwest Washington tonight. Winds will affect inland
areas as well as the coast. This system will also spread rain across
the forecast area, with snow in the Cascades tonight through Sunday.
Another weaker low pressure system is expected to move onshore near
the OR/CA border Sunday night, continuing chances for showers.
Seasonably damp weather looks to continue well into next week as a
series of frontal systems move into the West Coast from the Pacific,
though there may be a drying trend toward the end of the week.

&&

.SHORT TERM...Tonight through Tuesday...Models appear to be settling
in a solution for the low moving up the coast tonight, with the
biggest remaining issue the timing. Mid level water vapor channel
continues to show a small but persistent area of drying associated
with a shortwave rounding the base of the upper low in the vicinty
of 39N 125W. Visible imagery suggests a stretched out low center
near 40N. Ensembles generally indicate the low moving north this
evening to a point off the south OR coast by 00Z aided by the
shortwave lifting north with it. The low then weakens as the main
low reforms further north. Wind fields in general not quite as
strong as seen in models yesterday at this time, but still favorable
for a brief period of strong winds tonight as strong sw to west
winds on the south side of the low move north, and strong pressure
rises follow the low up the interior valleys. Overall the previous
forecast looks mostly on track, so expect to make only minor changes
to wind forecasts for tonight. The onset of peak winds looks like
early evening along the central OR coast, then shifts north, with
peak winds likely done over sw WA by 12Z. The main band of rain
preceding this low, and there hasn't been much of it, was already
lifting north across nw OR this afternoon. After a brief dry slot
moves through, precipitation turns more showery as seen in satellite
imagery. As the occluded front wraps in and cooler air aloft
associated with the upper trough push in, air mass becomes more
unstable. Model soundings suggests a threat for thunderstorms later
tonight, with the best chances along the coast. Inland areas, esp
considering the time of night, see a reduced threat, but for now
will retain the slight chance for thunderstorms late tonight into
the Willamette Valley.

Another shortwave rotating through the upper trough arrives Sun
afternoon, headed inland over western OR. General trend with models
is for a more or less open trough at the surface, although some
outlier model solutions include a respectable closed low in the
NAM80. As the trend overall though has been for a less organized
system, will go along with the open trough solution. This maintains
a showery onshore flow from late tonight into Sun night, with
progressively lowering snow levels as the cool trough alonft moves
across. This will translate into an extended period of snow showers
for the Cascades, with the heaviest showers likely occuring in the
strong flow behind the low later tonight, then gradually weakening
through Sun night. Will retain the winter weather advisory for the
Cascades through midnight Sun night.

A transient upper ridge moves across the region Mon and Mon night,
bringing a lull if not a stop to shower activity Mon. The next
system on the horizon is a deep wound-up low that models bring to
around 40N 140W by 00Z Tue. Isentropic charts show modest isentropic
lift shifting north across the forecast area Mon night into early
Tue with moisture mainly confined to mid and upper levels. Deeper
moisture is likely slower to arrive, more like Tue as a weakening
cold front arrives at the coast. This will bring increasing pops Mon
night and Tue, but weak dynamics will keep most areas with just
chance to likely pops.

.LONG TERM...Tuesday night through Saturday...The active pattern
continues over the northeast Pacific, with another system bringing
additional rain Tuesday night through Thursday. This should just be
a typical low impact front, as the system is originating from the
tropics. As a result snow levels will be coming up with this system
to 5500 to 6000 feet on Tuesday, and will start to gradually lower
behind the front to around 5000 to 5500 feet through the day on
Wednesday, and will hold around that level into late next week.
Thursday night the models are showing a shortwave ridge that looks
to develop, but overall this will have minimal impact except for a
slight increase in temperatures for the area. Forecast models show
another system approaching on Friday, but diverge significantly on
the track. This is making the end of the extended a challenge to
forecast, because of the uncertainty as to where the next system
will have the greatest impact. Therefore have kept temperatures
slightly above normal, and kept PoPs slightly lower. /42

&&

.AVIATION...Generally VFR across the area early this afternoon,
but there are still some stubborn pockets of IFR in the
Willamette Valley, mainly between KSLE and KEUG. Still expecting
this to dissipate by mid to late afternoon. Offshore low-level
flow to prevail through at least 03Z Sun. At 21Z the larger scale
KOTH-KGEG gradient was -10 mb while the Columbia Gorge KTTD-KDLS
gradient was at -5.5 mb. A complex low pres area off the South
Oregon and North California coast will continue to migrate north
this evening and tonight. This will bring increasing MVFR in the
00Z to 06Z Sun time frame, with gusty south wind developing at
KEUG and KONP between 03Z and 06Z. The south wind quickly spreads
north, reaching SW WA by around 07Z Sun. Will go with mainly
MVFR after 06Z Sun, although coastal areas likely to see a mix of
MVFR and VFR overnight through Sun morning. Models suggest a warm
front over SW Oregon late tonight will spread north Sun morning,
for the increased potential of MVFR or even IFR.

KPDX AND APPROACHES...VFR at the terminal as of 21Z. Offshore
flow through the Gorge will continue through at least 03Z Sun,
with the strongest east wind at the west end of the Gorge. Cigs
gradually lower through the late afternoon and early evening
hours, with -RA by 00Z Sun. Mix of VFR and MVFR after 03Z Sun,
with predominant MVFR overnight. Abrupt shift to south wind
expected around 07Z with gusts 25-35 kt. There is the potential
for LLWS late this afternoon through 05Z or so with surface east
to southeast wind and strong south to southwest wind around
FL020. Weishaar

&&

.MARINE...19Z ASCAT pass showed solid 35-40 kt wind over the
North California waters on the SE quadrant of the surface low.
The 03 hr NAM forecast appeared to be a little too far north
based on satellite imagery. The 12Z guidance is slightly slower
with the low pres progression northward. Latest NAM is a little
weaker with boundary layer wind speeds for this evening compared
to previous couple of runs. Strongest wind over the south zones
looks to occur between 01Z and 05Z Sun and 03Z to 07Z for the
north zones. Still holding at peak gusts to 45 kt. More model
differences arise for late tonight and Sun. The 18Z NAM appears
to be the most aggressive developing another surface low out near
43N 128W 12Z Sun. This is slightly more north than the 12Z
depiction. The 18Z version moves the low to near buoy 46050 by
18Z Sun, instead of Cape Arago as the 12Z showed. The ECMWF and
GFS are weaker with this feature. In any event, would anticipate
potential 25-30 kt gusts over PZZ255 and PZZ275 Sun morning.

Models show another deep low taking shape near 40N 138W Mon
night. The GFS indicates a sub-970 mb low pres center at that
time. This low looks to stay well offshore, but close enough to
produce gale force gusts over the outer waters Tue through Wed.
The active pattern continues late in the week with another strong
low forecast to move into the NE Pac.

Seas hovering around 10 ft early this afternoon, but that will
change tonight. The strong wind and associated large wind-wave
component will boost combined seas into the mid to upper teens
between 06Z and 12Z Sun. There is the possibility of 20 ft seas
should the wind be stronger than forecast and last longer than
expected. Seas ease below 10 ft Sun afternoon.

Guidance indicates possible 20-25 ft seas mid-week, but the
highest energy will be over the outer waters. Elevated seas,
generally teens or higher, look to persist late next week and
possibly into next weekend. Weishaar

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory from 7 PM this evening to midnight PST
     Sunday night for Cascades in Lane County-Northern Oregon
     Cascades.

     Wind Advisory from 8 PM this evening to 4 AM PST Sunday for
     Central Willamette Valley-Greater Portland Metro Area.

     Wind Advisory from 10 PM this evening to 6 AM PST Sunday for
     Lower Columbia.

     High Wind Warning from 6 PM this evening to 2 AM PST Sunday for
     Central Coast Range of Western Oregon-Central Oregon Coast.

     Wind Advisory from 6 PM this evening to 2 AM PST Sunday for
     South Willamette Valley.

     High Wind Warning from 8 PM this evening to 4 AM PST Sunday for
     Coast Range of Northwest Oregon-North Oregon Coast.

WA...Winter Weather Advisory from 7 PM this evening to midnight PST
     Sunday night for South Washington Cascades.

     Wind Advisory from 8 PM this evening to 4 AM PST Sunday for
     Greater Vancouver Area.

     Wind Advisory from 10 PM this evening to 6 AM PST Sunday for I-
     5 Corridor in Cowlitz County.

     High Wind Warning from 10 PM this evening to 6 AM PST Sunday
     for South Washington Coast-Willapa Hills.

PZ...Small Craft Advisory for winds until 6 PM PST this evening for
     Waters from Cape Shoalwater WA to Cascade Head OR from 10
     to 60 NM.

     Gale Warning from 7 PM this evening to 4 AM PST Sunday for
     Coastal Waters from Cape Shoalwater WA to Cascade Head OR
     out 60 NM.

     Small Craft Advisory for hazardous seas until 7 PM PST this
     evening for Coastal Waters from Cape Shoalwater WA to
     Cascade Head OR out 60 NM.

     Gale Warning from 5 PM this afternoon to 1 AM PST Sunday for
     Coastal Waters from Cascade Head OR to Florence OR out 60
     NM.

     Small Craft Advisory for Rough Columbia River Bar until 4 AM
     PST Sunday.
&&

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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.