Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 181710
AFDPQR

Area Forecast Discussion
National Weather Service Portland Oregon
909 AM PST Wed Jan 18 2017

.SYNOPSIS...A fairly strong frontal system is moving across the area
this morning. Cold air remains trapped in the Columbia Gorge and
Upper Hood River Valley, which will maintain a threat of freezing
precipitation through tonight. An upper level trough reaches the3
coast late tonight then shifts inland Thursday. Snow levels will
lower to just below the Cascade passes by Thursday. Offshore
low-level flow strengthens Friday for another threat of freezing rain
for the Central Gorge and Upper Hood River Valley. Unsettled
conditions persist through the weekend.
&&

.SHORT TERM...Today through Friday....Water vapor imagery this
morning shows a sharp low pressure center near 48N 126W heading
toward Vancouver Island. Models did a poor job with this feature and
even the 12Z NAM initialization did not seem to pick it up at all.
Wind gusts of 55 to 65 mph have been common along the coast overnight
through this morning, with gusts up to 75 mph common at headland
areas. Wind speeds have been slowly decreasing this morning and will
allow the coastal high wind warning to expire on schedule at 18Z.

Cold air remains trapped in the Columbia River Gorge, Upper Hood
River Valley and in the White Salmon drainage. Central Gorge
temperatures at 16Z were still in the mid 20s. Areas west of
Multnomah Falls have gone just above freezing. Will continue the Ice
Storm Warning but additional ice accretion will be much less than
last night. KTTD-KDLS gradient was -8.0 mb at 16Z, resulting in gusts
up to 40 mph at KTTD. Models have woefully under-forecast the
strength of the offshore flow through the Gorge. Do not see much
change in the offshore magnitude today. Made some adjustments to max
temperatures today, especially in the Gorge, Mt. Adams district
valleys and Upper Hood River Valley. Do not see Gorge areas east of
Multnomah Falls getting above freezing today. Areas away from the
Gorge have warmed nicely with mid 50s along the coast and into the
Central and South interior valleys.

Another disturbance near 40N 128W will rotate into the forecast area
today. There have been several lightning strikes associated with this
feature so will continue the mention of thunderstorms for the coastal
areas into the west slopes of the Willapas and Oregon Coast Range and
into the interior today.

Models agree that an upper level trough will reach the coast late
tonight and move inland Thursday. The 12Z KSLE sounding indicated a
freezing level of 8500 feet. The air mass will cool as the upper
trough approaches, with snow levels falling to near the Cascade
passes this evening, then slightly below pass level by Thursday
morning. The offshore low-level flow through the Columbia Gorge
really never ends. Higher resolution models such as the NAM are not
handling the offshore gradient all that well. There will continue to
be a threat of freezing rain in the Central Gorge and Upper Hood
River valley tonight and Thursday. As the overall air mass cools
tonight and Thu, there may be more sleet than freezing rain. Another
front will push into the region later Thu night and Fri, with rain
increasing. Another surface low settles into the NE Pac Fri. This
will strengthen the offshore flow through the Gorge for a continued
threat of freezing precipitation in the Central Gorge and Upper Hood
River Valley. Weishaar.

.LONG TERM...No Changes. Previous discussion follows...Friday night
through Monday...Models in good general agreement on keeping a closed
low off the WA and southern BC coast from Fri night through Sun
night, rotating a series of shortwaves through the region. The
shortwaves however show a tendency to split...with some energy
lifting ne through the Pacific NW and some energy headed down into
northern CA. identity of the waves quickly becomes difficult to
correlate between the models, so will generally have to limit pops to
high chance to low likely range at any given time. Models, EC in
particular, showing a tendency to hang onto an offshore flow through
the gorge, and it is not clear that the cold air ever truly gets
scoured out of the basin east of the Cascades. As such, will keep a
chance of freezing in for the gorge and hood river valley. Mon and
Tue models trend towards ridging aloft approaching the coast,
resulting in decreasing pops. EC is drier of the models, and as a
result tends to colder temps, and as such will still need to hang
onto some chance for freezing rain in the Gorge and Hood River Valley
all the way into Tue.

&&

.AVIATION...A cold front is pushing inland this morning. Expect a
mix of conditions through the morning, with MVFR/IFR occurring
during heavier rain bands. There will be a transition to a more
showery pattern this afternoon, and expect conditions to improve.
The interior TAF sites will likely by mostly VFR during the
afternoon and evening, with high end MVFR at the coast eventually
transitioning to VFR as well. Freezing rain will likely continue
in the Columbia River Gorge through at least 00z Thursday. Another
upper level disturbance will move onshore tonight, with will
enhance showers and may bring conditions back down to MVFR.

KPDX AND APPROACHES...Expect a mix of MVFR/IFR conditions through
the morning hours as a steadier band of rain moves through. Then
expect conditions to improve to mainly VFR this afternoon, with
occasional MVFR in showers. MVFR conditions may return late
tonight as an upper level disturbance comes onshore. Pyle

&&

.MARINE...The cold front over the coastal waters will move onshore
later this morning. Winds will gradually subside through the rest
of the morning, but will likely remain above gale force through
the early afternoon. Have downgraded the Storm Warning with a Gale
Warning through 3 PM. Winds should be generally 25 kt or less by
mid to late afternoon. Seas will also quickly drop today with the
decreasing winds. They have peaked around 23 to 28 ft this
morning, but should quickly drop back below 20 ft by early this
afternoon. They will then be into the mid teens by this evening.

A weak storm system moving eastward towards the region may
temporarily enhance winds across the waters late tonight or early
Thursday morning, but wind gusts should stay below Gale Force
criteria of 35 kt. Weak high pressure should produce a lull in the
winds Thursday before another front swings northeastward across
the waters Thursday night and Friday. Gale Force winds of 35 kt
appear increasingly likely during this period, but winds look to
remain mainly out of the southeast, which may keep the inner water
wind speeds lower.

Active weather will likely keep seas well into the teens through
the weekend. Models have been suggesting that a stronger surface
low pressure will impact the waters late in the weekend. This
latter storm system could be especially strong with seas climbing
above 20 ft. In addition, several swell trains arriving from a
more westerly direction late in the week and early next week will
stand a decent chance of necessitating High Surf products.
Pyle/Neuman

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Ice Storm Warning until 6 PM PST this evening for Central
     Columbia River Gorge-Upper Hood River Valley-Western
     Columbia River Gorge.

     High Wind Warning until 4 PM PST this afternoon for Central
     Coast Range of Western Oregon-Coast Range of Northwest
     Oregon.

     Flood Watch through late tonight for Central Coast Range of
     Western Oregon-Central Oregon Coast-Central Willamette
     Valley-Coast Range of Northwest Oregon-Greater Portland
     Metro Area-North Oregon Coast.

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

WA...Ice Storm Warning until 6 PM PST this evening for Central
     Columbia River Gorge-South Washington Cascades-Western
     Columbia River Gorge.

     Flood Watch through late tonight for South Washington Coast-
     Willapa Hills.

     High Wind Warning until 10 AM PST this morning for South
     Washington Coast-Willapa Hills.

PZ...Gale Warning until 3 PM PST this afternoon for Coastal Waters
     from Cape Shoalwater WA to Florence OR out 60 nm.

     Small Craft Advisory for Rough Columbia River Bar until 10 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. The area is
commonly referred to as the forecast area.


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