High Surf in Oregon, January 8, 2019

Area Forecast Discussion
National Weather Service Portland OR
900 PM PST Tue Jan 8 2019

Updated Aviation/Marine sections

.SYNOPSIS...An active weather pattern will continue through midweek,
with breezy offshore winds, valley rain, mountain snow, and a wintry
mix in the upper Hood River Valley and central Columbia River Gorge.
A quieter period should setup for the second half of the week into
next weekend.

&&

.SHORT TERM...Tonight through Friday...A broad low pressure system
continues its slow push toward the Pac NW today. The low center is
around 42N/135W, with an extensive frontal boundary wrapping around
the low up toward Vancouver Island, and then draped down along much
of the U.S. West Coast. The system is occluding and will be steadily
filling and weakening at its approaches over the next 24 hours.

The combination of strong low pressure offshore, combined with weak
high pressure east of the Cascades, is resulting in a significant
offshore pressure gradient today. The KTTD-KDLS gradient has now
strengthened to -10.5 mb. Even more impressive, the KOTH-KGEG
gradient has been hovering between -18 to -20 mb through most of the
day. The typically windy spots around the west end of the Gorge have
been blowing through the day, with Crown Point up around 80 mb, and
areas such as Corbett around 50 to 60 mph. However, the more synoptic
scale offshore gradient is resulting in gusty east winds across a lot
of the rest of our CWA as well. This is also helping to keep winds
near the west end of the Gorge and around the eastern portions of the
PDX/Vancouver metro area a little lower than we would typically see
with a gradient this strong. These winds will remain fairly steady
through tonight and much of tomorrow.

A leading warm front has moved through the CWA from south to north
today, bringing widespread moderate precipitation to the area.
Amounts have generally been around 0.25-0.5 inch across the CWA, with
some locally higher amounts in the higher terrain. The offshore winds
have kept temperatures near or just below freezing through much of
the day in the upper Hood River Valley and portions of the central
Columbia River Gorge. There were numerous reports of accumulating
snow up to a couple of inches in these areas this morning. However,
the latest surface observations show that temps are now mostly above
freezing, and precipitation has tapered off considerably over the
past couple of hours. Precipitation will continue to taper off later
this afternoon and this evening behind the warm front. There will be
occasional light precipitation through tonight, but amounts should
be minimal. There will also continue to be potential for some light
snow or freezing rain in the upper Hood River Valley and around Hood
River, but impacts should be minimal.

The parent upper level trough will swing up toward Vancouver Island
during the day Wed. This will drive the occluded front onshore and
through the region. Winds will become southeasterly and fairly gusty
along the coast during the late morning and early afternoon hours,
likely gusting 45 to 50 mph along the beaches and exposed coastal
headlands. A band of steadier precipitation will also move through
with the front, mainly during the afternoon and evening hours. We
will need to keep an eye on temps in the gorge and Hood River Valley
again, but given the timing of the precip, it looks unlikely that
there will be any significant additional wintry precipitation in
these areas. Snow levels will remain fairly high as well, generally
5000-5550 feet, so the Cascade passes should have only minor
accumulations through Wed night. However, with the continued easterly
flow, areas around Mt Adams and the east slope of Mt Hood could see
snow levels down lower.

Showers will linger into the Wed overnight and Thu morning period as
the upper trough moves through. A shortwave ridge building over the
region Thu should result in showers quickly tapering off, and think
most of the region is dry Thu afternoon and evening. Then Fri looks
to remain dry as well. It also appears that offshore flow will begin
to strengthen again Fri as the upper level ridge moves east of the
Cascades and a splitting low pressure system approaches offshore.
Pyle

.LONG TERM...Friday night through Tuesday...It appears that we are in
for a period of rather quiet weather over the weekend and into the
first half of next week. The fcst models are showing several low
pressure systems approaching the Pac NW during this time, but they
are also trending toward splitting well offshore. This would result
in mainly dry conditions across the CWA with temps right around
seasonal normals, along with more offshore flow. It is possible that
one or two of the fronts will hold together enough to generate some
light precipitation for portions of the CWA. At this time, the best
chances would appear to be Sat night into Sun, and Tue into Tue
night. Pyle

&&

.AVIATION...Moist southerly flow aloft will continue to
bring primarily VFR conditions with occasional bouts of rain
through 06z Thursday. Steadier rain with an approaching front may
produce a couple hours of MVFR conditions around 21z Wednesday near
the coast and near 00z Thursday for inland taf sites, though.

KPDX AND APPROACHES...Moist southerly flow aloft will continue to
bring primarily VFR conditions with occasional bouts of rain
through 06z Thursday. Low level easterly winds should become
increasingly shallow on Wednesday so wind shear will likely
become problematic at the terminal after ~18z Wednesday as
southerly winds increase aloft. /Neuman

&&

.MARINE...A broad low pressure system moving northeastward
towards the northern tip of Vancouver Island will spread Gale
Force southerly winds northeastward across the waters tonight and
Wednesday morning. Wind gusts should peak around 45 kt across the
waters either late Wednesday morning or midday Wednesday. A cold
front will then sweep across the waters early in the afternoon
and result in winds decreasing during the second half of the
afternoon and evening hours. Seas should gradually increase
tonight and rise into the mid to upper teens. Expect seas to
climb into the 20 to 25 ft range towards midday Wednesday before
subsiding back into the low to mid teens towards late Wednesday
evening or early Thursday morning.

Models continue to indicate additional surface low pressures will
move northward primarily between 130-140W Thursday through early
next week. This will likely produce several rounds of Small
Craft Advisory level south to southeasterly winds of 20 to 30 kt
across the waters. Cannot rule out Gale Force winds developing at
some point, but at this point, it seems these would be confined to
the far outer waters beyond 40 NM given the pattern. As a result,
seas should be a bit more subdued once we move past tomorrow and
expect seas to generally hover in the high single digits to low
teens for much of the next week once tomorrow is over. /Neuman

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for winds until 10 PM PST this evening for
     Waters from Cape Shoalwater WA to Cascade Head OR from 10
     to 60 NM.

     Gale Warning until 10 PM PST Wednesday for Waters from Cape
     Shoalwater WA to Cascade Head OR from 10 to 60 NM.

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

     Small Craft Advisory for winds until 10 AM PST Wednesday for
     Coastal Waters from Cape Shoalwater WA to Florence OR out
     10 NM.

     Gale Warning from 10 AM to 10 PM PST Wednesday for Coastal
     Waters from Cape Shoalwater WA to Florence OR out 10 NM.

     Small Craft Advisory for hazardous seas until 10 AM PST
     Wednesday for Coastal Waters from Cape Shoalwater WA to
     Florence OR out 10 NM.

     Gale Warning until 10 PM PST Wednesday for Waters from Cascade
     Head to Florence OR from 10 to 60 NM.

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

&&

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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.