High Wind in Oregon, March 7, 2017

Area Forecast Discussion
National Weather Service Portland OR
945 AM PST Tue Mar  7 2017

.SYNOPSIS...A wet and unsettled weather pattern will continue
through the remainder of the week with periods of valley rain and
mountain snow. Today will be particularly windy along parts of the
Oregon coast and Coast Range as a low pressure system moves inland
near the Columbia River late in the day. With extended periods of
rain, some minor flood issues could arise late in the week.

&&

.SHORT TERM...Today through Friday...A relatively weak surface low
pressure system is currently off the Oregon coast and forecast by
most models to move ashore near the mouth of the Columbia River.
However, its current location based on satellite imagery is not
immediately obvious, which is a little concerning given it's supposed
to make landfall in the next 6 hours. There is an area of deeper
shower activity currently approaching the Oregon coast that may be
tied to the low level circulation, but this convection appears more
tied to an area of elevated instability along the warm front. Even
though no lightning has been detected yet, did add a slight chance
mention of thunder to the southern half of the CWA as this area of
elevated instability moves eastward. Given models seem to rarely
underdo surface low pressures by as much as satellite may suggest at
this point in the immediate short term, will keep the current wind
headlines as is and monitor SLP and wind trends accordingly.

Widespread light rain due to isentropic lift has spread northeastward
across the entire CWA this morning. Rainfall rates have been
primarily around a tenth of an inch or less per hour. As the
aforementioned area of elevated instability moves eastward, we
should see some areas of localized higher rainfall rates spread into
the region. Model guidance and satellite trends suggest Lincoln,
Lane, Benton & Linn Counties will likely be most susceptible to
these higher rainfall rates. Snow levels are still hovering around
2000 ft near the northern Cascades, but should rise into the 3500-
5000 ft (highest towards Lane County and lowest towards the south WA
Cascades) range this afternoon and tonight so will drop the Winter
Storm Warning for the foothills shortly. As the aforementioned low
pressure shifts east of the Cascades this evening, strong southwest
to westerly flow at 850mb should strengthen the orographic
enhancement of precipitation so will likely keep the Winter Storm
Warnings for the Cascades going into tonight.

Models are in good agreement the trailing 850mb baroclinic zone from
the aforementioned low pressure system will stall over the southern
half of our CWA later tonight and Wednesday. This will likely produce
periods of valley rain and mountain snow during this time with
considerably higher snow levels towards Lane County vs. Mt Hood and
the south WA Cascades. Areas farther north may need Winter Wx
Advisories once the Winter Storm Warnings are finished.

Models are in decent agreement another developing surface low
pressure will move northeastward across the northeast Pacific late
Wednesday and Thursday. This should act to lift the aforementioned
baroclinic zone northward as a warm front late Wednesday night and
Thursday. As we enter the warm sector, precipitable water values in
excess of an inch will likely push into the region and IVT values
increase to around 500 kg/ms. Given the wet weather of late, a few
of our more flood prone rivers may push up towards minor flood stage
Thursday and/or Friday so will likely issue an ESF later today. The
good news is that shortwave ridging looks to bring a drying trend
Friday. /Neuman

.LONG TERM...No Changes. Previous discussion follows...Thursday night
through Monday...The models say a cold front from a rather strong low
will sweep through southwest Washington and northwest oregon Thursday
night with pretty good rains, mountains snows, and coastal wind. The
models vary some after that, but indicate as a whole that another
front will move through around Saturday with another about Monday.
The models are backing away from being very cold next weekend, with
conditions still below normal but much closer to seasonal normals
than we have seen recently. Tolleson

&&

.AVIATION...Steady rain will continue through tonight. A low pres
system approaches the coast today and moves onshore this
afternoon. Expect conditions to gradually deteriorate through the
rest of the morning, with mainly MVFR conditions expected. The
leading warm front will move onshore this afternoon...likely
bringing even more deterioration with some IFR developing. Also
can't rule out some isolated thunder with the warm front. The
trailing cold front will come through later this afternoon
through this evening, progressing from NW to SE. Rain will taper
to showers behind the cold front.

As the low pres comes onshore...expect some particularly gusty SW
winds to affect the coast mainly south of KAST roughly 18Z-00Z.
The TAF site to be most impacted will be KONP, where south gusts
40-45 kt appear likely. Gusts 30-35 kt are probable in the
Willamette valley as the surface low crosses through SW
Washington.

KPDX AND APPROACHES...Steady rain continues through today. Expect
predominantly MVFR conditions to develop later this morning.
Conditions deteriorate further this afternoon, with IFR becoming
likely between 20Z-00Z. A shift in the surface low track toward
the north makes it look more likely that gusty S winds will
affect the terminal late this afternoon. Expect a period of gusts
30 to 35 kt. Rain tapers to showers this evening, but expect MVFR
conditions to continue through tonight. Pyle

&&

.MARINE...A low pres system moving inside of 130W this morning
will swing NE and move onshore around the Long Beach peninsula
this afternoon with a strength of around 1006-1008 mb. South
winds will pick up considerably to the south of the low later
this morning and this afternoon. The main impacts will be over
the Oregon coastal waters, where a 3-4 hr stretch of 40 to 45 kt
winds are expected. There may be some coastal jet enhancement
between 5-30 nm offshore, where some gusts to 50 kt can be
expected. A Storm Warning is in effect for zones PZZ255/275.
Winds to the north of the low over the Washington waters will be
much less, generally 20 kt or less.

Large and steep wind waves will accompany the winds, and the
seas may briefly build up into the upper teens. Winds and seas
decrease considerably this evening. There is then a period of
quieter weather through early Thu. Another low will form along a
baroclinic zone late Thursday or Friday, and bring another round
of strong winds and large seas. Pyle

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Storm Warning until 4 AM PST Wednesday for Northern
     Oregon Cascades.

     Winter Storm Warning until 10 AM PST this morning for Northern
     Oregon Cascade Foothills.

     Winter Storm Warning until 10 PM PST this evening for Cascades
     in Lane County.

     High Wind Warning from noon today to 8 PM PST this evening for
     Central Coast Range of Western Oregon.

     High Wind Warning until 6 PM PST this evening for Central
     Oregon Coast.

     High Wind Warning from noon today to 6 PM PST this evening for
     North Oregon Coast.

WA...Winter Storm Warning until 4 AM PST Wednesday for South
     Washington Cascades.

     Winter Storm Warning until 10 AM PST this morning for South
     Washington Cascade Foothills.

PZ...Gale Warning until 5 PM PST this afternoon for Coastal Waters
     from Cape Shoalwater WA to Cascade Head OR out 60 nm.

     Storm Warning until 5 PM PST this afternoon for Coastal Waters
     from Cascade Head OR to Florence OR out 60 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.