High Wind in Oregon, February 14 to 15, 2017

Area Forecast Discussion
National Weather Service Portland OR
851 PM PST Tue Feb 14 2017

.SYNOPSIS...The next system will slowly spread rain onshore tonight,
becoming heavy at times especially Wednesday and Wednesday night. The
front finally moves onshore and through southwest Washington and
northwest Oregon Thursday morning. This system will be accompanied an
initial surge of wind near the Oregon coastal headlands later tonight
and early Wednesday, followed by stronger and more widespread coastal
winds along the coast Wednesday afternoon into early Thursday. East
wind will persist in the Gorge reinforcing cold air in the Columbia
River Gorge and resulting in the potential for significant ice east
of about Multnomah Falls and in the Hood River Valley. We will see
showery weather for the remainder of Thursday through next weekend,
with snow levels just below the passes in the Cascades.
&&

.SHORT TERM...Tonight through Friday...Minimal changes to the current
forecast. Evening water vapor imagery shows a baroclinc zone inside
125W. There is a strong jet feeding this frontal zone as noted by the
nice dark notch near 45N 130W at 04Z. AMSU Blended Precipitable Water
Product from 0143Z indicated a large swath of 1.5 inch values near
the coast and over the coastal waters. METARS and KRTX dual-pol
doppler radar show light precipitation from the coast to the
Willamette Valley and SW Washington lowlands.

The frontal zone will slowly move onshore tonight. An initial wave
along the boundary appears it will bring some headland high wind
along the Oregon coast later tonight and Wednesday morning. The
RAP13, HRRR and HiRes-ARW show 40-50 kt boundary layer wind speeds
along the coast 10Z Wed.  Models still indicate a second and stronger
surface low that moves north along the coast later Wednesday and
Wednesday night. The NAM has a core of 60-65 kt boundary layer wind
speeds along the central Oregon Coast 21Z Wed. The GFS is slightly
weaker, topping out at 60 kt. The 12Z ECMWF has 60-65 kt wind speeds
in the 0-1km layer. The 850 mb NAM wind speeds are quite impressive
Wed afternoon and evening, peaking around 80 kt along the coast 03Z
Thu. Current wind warnings look good.

The precipitation type in the Gorge is the main forecast issue. At
04Z the KTTD-KDLS gradient was about -7.0 mb. However, the more
synoptic scale KOTH-KGEG gradient was at -7.7 mb. The east wind
through the Gorge is purely gap flow. Models, even the higher
resolution versions, have been rather poor with the offshore
gradient. Generally, these models have been weakening the gradient
way too fast, as has been the case for much of this winter. The other
concern is the cold air source region. Areas in the Gorge between
Hood River and The Dalles made it to near 40 degrees. Locations is
east Skamania County and West Klickitat County were in the lower to
mid 40s. As of 04Z temperatures were slightly above freezing in much
of the Hood River Valley and also across much of the Central Gorge.

Model soundings provide little additional confidence in freezing
precipitation. The 12Z NAM sounding for a point near Hood River
initialized at least 5 degrees too cold. At 04Z the model sounding
projected a surface temp of around 26F, again about 5-6 degrees too
cold. The 4km NAM was much better, but still slightly too cool at the
surface. In any event, the 4km NAM shows a 4-5 hr period of freezing
precip, from 10Z to 14Z Wed, then a transition to rain. Models are
notorious for warming things up way too soon.

This system will produce substantial rains as well. Look for rain
most areas Wednesday into Thursday morning, heaviest along the south
Washington and north Oregon coast and the adjacent coastal mountains,
as well as into the south Washington Cascades. Currently, no rivers
are forecast to approach flood stage but expect significant rises. We
will continue to monitor developments as the event approaches.

The front moves through Thursday morning with showers spreading in.
Snow levels will lower to near the passes in the Cascades later
Thursday.

The next system heads mainly south into California on Friday, though
a few showers do spread into our area during the day. Snow levels
will remain near or below the Cascade passes Friday. Weishaar

.LONG TERM...Friday Night through Tuesday...The models show a series
of mostly weaker systems affecting our forecast area during the
period but details and timing issues are not very consistent from
model to model. There is some indication of a more organized low
early next week but again there are a lot of variations on this theme
in the models. For now have used a broader brush for the weather with
mid range PoPs most periods. If the low develops off the coast early
next week, we could see some east wind in the Gorge again and
possibly some winter precipitation. Tolleson
&&

.AVIATION...-RA has arrives across much of the area with
continuing VFR conditions. Expect heavier, steadier rain and
MVFR cigs/vsbys for the coast by 10-14z and into interior closer
to 12-16z. MVFR conditions and RA continue into Wed. Gusty south
winds with gusts up to 25 kt for the coast late tonight through
early Wednesday. East winds through the Columbia River Gorge will
result in 35 kt gusts near and at KTTD. Freezing rain expected
for the Central Columbia River Gorge and Upper Hood River Valley
will result in icy surfaces for east of Cascade Locks including
Hood River. Coastal winds out of the south pick up further
Wednesday evening with gusts to 40 kt possible.

KPDX AND APPROACHES...Gusty east winds will persist out of gorge.
MVFR cigs and/or visibilities late tonight into Wed morning with
light rain. Tempo MVFR possible throughout the day Wed. Bowen

&&

.MARINE...An active weather pattern will result in strong winds
and elevated seas the next several days. South winds will
increase tonight as a frontal system moves across the waters and
expect gales to develop. Don't have any obs to back it up, but
suspect there are gales beyond about 20 nm offshore this evening
while an easterly component is likely keeping winds closer to
shore a bit lower. However, the easterly gradient is weakening,
so expect winds across all of the waters to increase to gales by
late tonight. Winds will further increase Wednesday afternoon
and evening with a stronger front. Models have been persistent in
forecasting storm force winds over the waters starting as early
as around midday Wednesday, so will continue the Storm Watch and
let the next shift take one last look before potentially
upgrading to a warning.

Seas appear to range from about 8 to 12 ft this evening, at least
within about 15 nm of the coast where we have data. The seas
will be confused and a combination of two separate swell trains
one from the NW and another from the SW with large differences in
wave periods. The SW swell will rapidly build to above 20 feet
Wednesday morning as a smaller (6 ft) longer period (18 seconds)
swell slowly builds. Didn't make too many changes to significant
wave height forecast, but did continue to lean towards the
latest NWPS output which has seas peaking 24-26 ft starting
Wednesday evening.

Seas decrease slowly during the day Thursday, reaching the mid
teens by the day's end and then falling further through Friday. A
progressive pattern remains through at least the weekend with
continued threat for winds above 20 kt. However, right now it
looks like seas should remain below 10 ft starting Friday night.
Bowen

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Ice Storm Warning from midnight tonight to 6 AM PST Thursday
     for Central Columbia River Gorge-Upper Hood River Valley-
     Western Columbia River Gorge.

     High Wind Warning until 10 AM PST Wednesday for Central Oregon
     Coast-North Oregon Coast.

     High Wind Warning from 1 PM Wednesday to 6 AM PST Thursday for
     Central Oregon Coast.

     High Wind Warning from 5 PM Wednesday to 6 AM PST Thursday for
     North Oregon Coast.

WA...High Wind Warning from 7 PM Wednesday to 8 AM PST Thursday for
     South Washington Coast.

     Ice Storm Warning from midnight tonight to 6 AM PST Thursday
     for Central Columbia River Gorge-Western Columbia River
     Gorge.

PZ...Small Craft Advisory for Rough Columbia River Bar until 4 PM
     PST Wednesday.

     Storm Watch from Wednesday morning through late Wednesday night
     for Waters from Cape Shoalwater WA to Florence OR from 10
     to 60 nm.

     Gale Warning until 10 AM PST Wednesday for Waters from Cape
     Shoalwater WA to Florence OR from 10 to 60 nm.

     Storm Watch from Wednesday evening through late Wednesday night
     for Coastal Waters from Cape Shoalwater WA to Florence OR
     out 10 nm.

     Gale Warning until 6 PM PST Wednesday for Coastal Waters from
     Cape Shoalwater WA to Florence OR out 10 nm.

&&

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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.