Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Portland or
322 am PST Thu Jan 17 2019
Synopsis...a vigorous low off the Oregon coast will push northeast
today. This will maintain showery weather across much of the region,
along with breezy conditions. Next system will push into the region
later Friday, with rain increasing. This will bring heavy rain at
times Fri night. This front will stall to our south Sat, but lifts
back across the area Sat night. Rainy weather for Sat night and sun.
Then showers decreasing, with drier weather to start next week.
Short term...today through Saturday...great swirling low sitting off
the Oregon coast this am. This low will continue to track to the
north-northeast today, and into Vancouver Island tonight. Bands of
showers will move onshore today into tonight.
Have limited boost of instability this am, and feel just enough to
support an isolated thunderstorm or two along the Oregon coast and
extending offshore. Will keep that in the forecast for this am. Main
effects from the low will be the increasing southerly winds today
along the coast, and over the higher terrain. Will see gusts 45 to 55
mph along the coast, with the higher winds relegated to those
headlands and open beaches that typically feel strong south winds.
These south winds will bring milder temperatures to the region, with
highs getting into the lower 50s. For inland areas that have seen
some chilly days recently, this chance will feel quite Spring like.
Even the east winds in and around the Columbia Gorge will gradually
ease today, and become westerly later this evening.
Speaking of The Gorge, weather will be a mixed bag this am.
Temperatures west of Cascade Locks have hovered just above freezing
this am, and feel that will continue to be the case through this am.
So, will end the Winter Weather Advisory for that area. But to east
of Cascade Locks, temperatures generally 31 to 33 deg. Any
precipitation will likely fall as snow or sleet, or a combination of
snow, sleet and freezing rain at times this am. But, think amounts
will be light, with generally less than an inch of new snow.
Snow has subsided in the Hood River Valley, with just occasional
flurries early this am. Generally, have seen about 2 to 5 inches of
snow in the valley overnight, with heaviest accumulations from ODell
southward to Parkdale. Will continue to see occasional snow showers
this am, with an inch or less of new snow. But, like in The Gorge,
can not rule out some spotty light freezing rain or sleet at times.
Will maintain Winter Weather Advisory through 10 am for the central
Columbia Gorge and the Upper Hood River Valley.
Snow levels holding around 4000 feet for the Cascades, where will see
another 3 to 6 inches of snow today and again tonight, but bit less
over Lane County where snow levels will be higher.
National oceanic and atmospheric administration satellite imagery shows next wave developing out at 34n 156w,
and has decent tap of subtropical moisture feeding it. This is the
system that will arrive later Fri, with warm front lifting across
western Oregon. So, will see rain increasing Fri afternoon ahead of
the warm front. Models continue to be rather aggressive with qpf, and
agree with the trends. Even models have a plume of precipitable water
values of 1.25+ aimed at western Oregon by Fri evening, then this
shifts southward overnight. So, this should support rather modest
rainfall amounts for Fri night, with heavy rain at times, especially
along the coast and coastal mountains. Rainfall likely in 1.50 to
3.00 inches of rain for the coast and Coast Mountains. But, even
these estimates may be on the low side, as typically models are bit
low on rainfall totals in these setups. Farther inland, generally
around an inch for i5 corridor and Willamette Valley. Snow levels
rising, so even Cascades will see just rain falling at the passes Fri
Front shifts inland and southward early Saturday, with rain
transitioning to showers. But with the front not too far south, will
see more steady rain continuing over Lane County and into the Oregon
Another beach hazard expected Thursday and Thursday night is large
surf. A high surf warning has been issued for the central Oregon
coast, and a high surf advisory for the north Oregon and South
Washington coast. The GFS-based enp wave guidance and European model (ecmwf) wave
model continue to show 20-25 ft waves impacting the surf zone
Thursday through Friday morning. 12z spectral guidance for buoy 050
indicates peak wave heights of 25 ft with a dominant period around 17
seconds beginning late Thu morning. This happens to occur a couple
hours after peak high tide. Our local coastal flood index tool
indicates an energy index of 160-170 with a 30-degree incidence angle
offset (swell direction 240 deg vs. 270 deg). This is very close to
high surf warning criteria. The tool also output a coastal flood
index (cfi) of 20-21. Typically 22 is the threshold for coastal Flood
Warning. Based on recorded impacts from previous events, opted to go
with a high surf warning for the central Oregon coast. Overall wave
energy will be a little lower for the north Oregon and South
Washington coast so went with a high surf advisory. /Rockey.
Long term...Saturday night through Tuesday...as the upper level
trough responsible for the atmospheric river shifts overhead Sunday,
precipitation should turn more showery in nature, and the snow levels
will lower. An upper trough will maintain showers through Sunday with
snow levels around 4500-5500 feet. Models are in great agreement that
an upper level ridge will build Monday and Tuesday for drier weather,
and cooler nights. ~Tj
Aviation...apart from fog down around eug, dry easterly flow is
keeping all other terminals VFR. With increasing southerly winds
over the next few hours, expect eug will clear out to VFR as
well. VFR conditions continue through this morning, with showers
picking back up midday today. Heavier showers could occasionally
lower cigs and vis to MVFR. Otherwise, predominantly VFR
conditions continue through tonight.
Kpdx and approaches...VFR conditions this morning. Showers
increasing midday today. Cigs and vis could occasionally lower to
MVFR under heavier showers. Predominantly VFR conditions continue
through tonight. East winds continue through the Columbia Gorge,
with gusts to 35 kt at ttd, but 10 to 15 kt near pdx. Winds will
turn southerly at pdx this afternoon, but east winds will likely
continue close to the Columbia Gorge. -McCoy
Marine...strong 972 mb low pressure system off the coast of
Oregon today. This is generating southerly gales across our
coastal waters. This will also bring in large swell, building
seas to 25 to 28 feet, 30 feet just to our south off the coast of
southern Oregon. Seas peak around midday today through this
afternoon, around the same time winds are peaking with gusts up
to 45 knots. Winds will be decreasing this evening as the low
lifts off to our north. This will also allow for seas to drop
below 20 feet by Friday morning.
Another strong low pressure system is expected to come up from
the south, tracking fairly similarly to the system today. This
will bring another round of high-end gales Friday and Friday
night. We will also see seas peak back up around 20 feet late
Friday night into Saturday morning.
Unsettled pattern continues into the weekend, but behind the
Friday system, nothing looks as strong as these previous two
systems in the models at this time. -McCoy
or...high surf advisory from 10 am this morning to 10 am PST Friday
for north Oregon coast.
Winter Weather Advisory until 10 am PST this morning for
central Columbia River gorge-Upper Hood River Valley.
High surf warning from 10 am this morning to 10 am PST Friday
for central Oregon coast.
Washington...high surf advisory from 10 am this morning to 10 am PST Friday
for South Washington coast.
Winter Weather Advisory until 10 am PST this morning for
central Columbia River gorge.
Pz...Gale Warning until 10 PM PST this evening for coastal waters
from Cape Shoalwater Washington to Florence or out 60 nm.
Small Craft Advisory for rough Columbia River bar until 4 am
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