Wind Advisory 1, NWS Portland, OR

Area Forecast Discussion
National Weather Service Portland OR
900 AM PST Thu Mar 8 2018

.SYNOPSIS...Wet and blustery weather will prevail today as a low
pressure system off the south Washington coast lifts northeast and
moves inland across the Olympic Peninsula today. Cascade snow
accumulations will mostly be limited to elevations above pass level.
Cooler weather, lowering snow levels, and plenty of showers continue
Friday. A few showers are possible with a warm front Saturday or
Saturday night, then southerly flow aloft may bring the warmest
temperatures of the year thus far, with highs likely reaching the
60s for the lowlands Sunday and Monday. Rain chances may return by
the middle of next week.

&&

.SHORT TERM...Today through Saturday...Radar identified surface low
of around 996 mb was just off the south WA coast this morning, and
expected to lift nne today and continue to fill. Winds this morning
appear to be peaking already long the central Oregon coast, with the
switch from offshore to onshore winds moving steadily north up the
coastline this morning. With the low already off the WA coast and
the switch to onshore winds seen in surface observations already
north of KTMK, will go ahead and move the start time for the south
WA coast high wind warning up to start with the new forecast
issuance. Expect winds to begin subsiding by early afternoon, but
not enough confidence in when exactly to end the warnings earlier,
so will just have to wait and see how winds trends through early
afternoon before ending any of the warnings. Winds in the central
and south Willamette Valley already gusting in in the range of 35 to
40 mph this morning. With some gusts already reaching over 40 mph,
and gradients expected to peak on the order of 4 to 5 mb between
KPDX and KEUG, will go ahead with wind advistories for the inland
valleys into the early and mid afternoon. Rain already spreading in,
with the cold front pushing through the Coast Range this morning.
Will see rain transition over to showers behind the front during the
day today. Snow levels will keep snow limited to higher terrain in
the Cascasdes today. Orographics with the southerly low level winds,
transitioning to westerly late in the day, will tend to most favor
the south WA Cascades for significant snow accumulations, with
lighter amounts down in the OR Cascades today, so the winter
advisory for the south WA Cascades looks reasonable.

An upper level shortwave moving moves across the region, in
particular WA, tonight will keep the threat for showers going
tonight, while the westerly flow will tend to favor the north to
south oriented mountains due to orographics. Shower threat becomes
greatly reduced once the shortwave clears the region later Fri. and
we get a bit of upper level ridging Fri night and low level flow
turns offshore. A weak shortwave pushing into the ridge Sat returns
a slight chance for showers, mainly to the southern parts of the
forecast area.

.LONG TERM...Saturday Night through Wednesday. No changes. Previous
discussion follows. While there is still some model disagreement in
the details, model consensus seems to be pointing toward a drier,
warmer period Sunday and Monday, which may last into Tuesday. Agree
with previous shift's idea that upper level ridging will build
across the western United States, but the position of the resulting
ridge axis will be key as to whether we see a slightly milder,
showery pattern, or all-out Spring weather with temps pushing well
into the 60s for the inland valleys. Am favoring the drier/warmer
solution, and not just because I'm desperate for warmth. Feel that
downstream features will have a lot of say in where the ridge axis
lies early next week; the next potential East Coast nor'easter may
have a significant impact. Prefer the 00z GFS solution in the
handling of downstream features, mainly since rapidly intensifying
lows tend to curl north, rather than the 00z ECMWF's idea of keeping
Monday's low well off the Eastern Seaboard. This stronger nor'easter
solution would likely amplify the pattern, creating somewhat of a
backup in the flow pattern across the North America. This would tend
to favor a Western ridge axis that is further west, which would
favor warmer and drier weather for us early next week. That said,
even the drier/warmer GFS brushes the Pac NW coast with northward
moving systems, so there will likely be at least some cloud cover.
Therefore we held temps in the lower to mid 60s for the lowlands
despite the fact that 00z GFS 850 mb temps could support temps near
70 deg F if all went perfectly. All in all, confidence is fairly
high that it will feel at least a little more like spring Sun/Mon,
and there is the potential of it feeling a lot more like spring.
Weagle

&&

.AVIATION...A strong low pressure system offshore of the south
Washington coast is generating gusty winds across the region with
widespread S-SW wind gusts of 30-40 kt. this morning. The gusty
winds will continue through the afternoon. MVFR conditions for
the coast through at least this evening and possibly through the
night. The coast may have localized IFR cigs too. Expect MVFR
conditions for the interior lowlands this afternoon and evening,
and possibly through the night. Could see some fog early Friday
morning.

PDX AND APPROACHES...Windy conditions this morning and early this
afternoon. S winds should shift to the SW around noon. Expect
MVFR conditions at times this afternoon. Rain will taper to
showers and winds will ease tonight. ~TJ
&&

.MARINE...Winds and seas have reached their peak intensity south
of Cascade Head this morning, and are close to peaking off of the
north Oregon and South Washington coast. Seas may build close to
20 feet the next hour or two offshore of the Columbia River Bar
with gusts to 40 kt. Seas are a combination of wind swell and
fresh swell and should subside to the mid teens in the late
afternoon, and down below 10 feet early Friday morning. Timing
of current Gale Warning looks good with Gales ending this
evening.

Fairly quiet ocean conditions Friday and this weekend with seas
below 7 feet and winds mostly below 15 kt. Offshore flow develops
Saturday and the waters beyond 20 nm could see gusts to around 2
kt. ~TJ

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory until 4 PM PST this afternoon for Greater
     Portland Metro Area-Lower Columbia.

     High Wind Warning until 6 PM PST this evening for Central Coast
     Range of Western Oregon-Coast Range of Northwest Oregon.

     Wind Advisory until 2 PM PST this afternoon for Central
     Willamette Valley-South Willamette Valley.

     High Wind Warning until 3 PM PST this afternoon for Central
     Oregon Coast-North Oregon Coast.

WA...Winter Weather Advisory until 10 PM PST this evening for South
     Washington Cascades.

     Wind Advisory until 4 PM PST this afternoon for Greater
     Vancouver Area-I-5 Corridor in Cowlitz County.

     High Wind Warning until 6 PM PST this evening for South
     Washington Coast-Willapa Hills.

PZ...Gale Warning until 4 PM PST this afternoon for Waters from Cape
     Shoalwater WA to Florence OR from 10 to 60 NM.

     Small Craft Advisory for Rough Columbia River Bar until 1 AM
     PST Friday.

     Gale Warning until 6 PM PST this evening 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. This area is
commonly referred to as the CWA or forecast area.