High Wind in Oregon, November 26 to 27, 2018

Area Forecast Discussion
National Weather Service Portland OR
349 PM PST Mon Nov 26 2018

.SYNOPSIS...Upper level low pressure approaches from the Pacific
today, and an associated cold front pushes inland early Tuesday. This
will bring increasing chances for rain tonight with a period
of moderate to heavy rain possible, particularly near the coast.
Behind the front, precipitation turns more showery later Tuesday,
with a slight chance for thunderstorms across much of the area. Cool
and showery conditions likely continue through much of the week as
the upper level trough moves across the region.

&&

.SHORT TERM...Tonight through Thursday...The main axis of rain this
afternoon remains focused in western Washington, with the southern
portions of the rain band extending south into our forecast area.
Generally speaking, the consistent rain is north of a roughly Newport
to Kelso line. A shortwave impulse continues to approach the
coastline, which will be the catalyst for pushing the associated cold
front across the region later tonight through early Tuesday. Strong
southerly low-level winds and satellite estimated PW values around
1.2 inches will bring strong moisture transport into the area. This
will bring a period of pre-frontal heavy rainfall tonight, especially
for the coastal areas. As the front approaches, expect that southerly
winds will also increase. While the trends in the model guidance have
been somewhat consistent, the observed gusts at places like Cape
Disappointment are already outpacing this guidance (gust to 58 mph
earlier this afternoon). As a result, have slightly increased the
forecast wind gusts for the beaches and coastal headlands, and have
also upgraded the watch to a High Wind Warning for these same
locations. The environment along the front may also aid in mixing
down some stronger winds to the surface. The current forecast is now
for gusts to 60-65 mph along the immediate coastline. However, given
a slight southeast component to the winds, the gusts in the coastal
communities will likely not be as strong (albeit, still breezy).

A showery pattern follows Tuesday in the post frontal air mass behind
the front. Forecast models continue to indicate a rather unstable
environment behind the front, and have continued to indicate a slight
chance of thunderstorms from the coastal waters all the way through
the Willamette Valley. These storms that develop are not expected to
be severe, but gusty winds and small hail can be expected with any
thunderstorms that do develop. Expect continued showers on Wednesday,
though at this point the deeper instability seems to fade so will not
introduce thunderstorm mention at this time for Wednesday.  Another
front pushes in on Wednesday bringing another round of widespread
rain across the area. By Thursday, forecast models begin to diverge a
little bit more significantly. It's possible that many of the
locations see a break in the rain in between stronger systems, but
cannot entirely rule out some lingering showers across some parts of
the area.   Cullen

.LONG TERM...Thursday night through Monday...The 12z GFS and 12z
ECWMF, are in agreement. The models both show what remains of a low,
which was the dominating feature through the middle of the week.
Embedded within this low, there looks to be a shortwave trough,
which will keep precipitation chances up from Thursday night through
Friday afternoon. Friday evening into Saturday has the next low
working its way into the area. It should be noted that this system
has been fluctuating with each model run, from a well defined 980mb
low, to a rather benign 1000mb low. Either scenario looks to bring
precipitation into the area through the later part of the weekend,
but as the models have been flip flopping on strength, the
confidence in how much precipitation is expected is difficult to
determine. Temperatures during this time frame start a slight
cooling trend. /42
&&

.AVIATION...A strong cold front is nearing the coastal waters
this afternoon. Light rain is spreading onshore ahead of the
front and will gradually increase in intensity tonight. MVFR
conditions have already developed along the coast and should
persist through most of the night. The interior remains VFR, but
should also deteriorate to MVFR by late this evening. As the rain
becomes heavier later tonight, some localized IFR vsbys are
possible. Southerly winds will also be quite gusty ahead of the
front. Expect 30 to 40 kt gusts at the coast, with 20 to 25 kt
gusts over the interior lowlands. The front should move onshore
by early Tue morning, and then move through the interior lowlands
by mid-morning Tue. Expect rain to taper to showers behind the
front, with a mix of VFR and MVFR cigs through the rest of the
morning, trending to mainly VFR in the afternoon. Lastly, there
is potential that we will see some thunderstorm activity right
along and behind the front at times Tue. The best thunder chances
will be at the coast.

PDX AND APPROACHES...Gusty east winds will continue through
tonight. Expect mid-level VFR cigs and light rain through this
evening. Rain will become moderate to heavy overnight, with MVFR
conditions developing by late this evening. The front is
expected to move through the terminal by around 15Z, with rain
tapering to showers behind the front. Some MVFR cigs are expected
in the post-frontal showers Tue. The offshore winds will switch
to SW Tue morning behind the front. Pyle

&&

.MARINE...A strong cold front is just outside our coastal waters
this afternoon. Southerly winds have been gradually increasing
through the day ahead of the front, and the latest buoy obs are
showing widespread gales across the waters right now. Expect the
winds to strengthen even a little further tonight and early Tue
morning right ahead of the front, with peak winds generally in
the 40 to 45 kt range. It is not out of the question that there
could be a few isolated gusts close to 50 kt. The front looks to
push onshore by 1 to 3 AM for the south WA and north OR coast,
the 3-5 AM for the central OR waters. Winds will become
southwesterly and drop off fairly quickly Tue morning behind the
front. There may be some gusts 20 to 25 kt through the day Tue.
We are also expecting some thunderstorm activity over the waters
Tue in the cool and unstable post-frontal air mass. Any
thunderstorms would bring the potential for some briefly stronger
gusts.

Seas are also steadily building today in response to the strong
winds. The latest observations are showing seas in the mid teens,
and they should continue to increase tonight, peaking in the
19-21 ft range. A long period westerly swell generated by this
system will arrive during the day Tue, which should keep seas in
the mid to upper seas through most of the day. Seas will then
gradually subside over the next few days, but the decaying long
period swell will probably keep seas near or above 10 ft through
most of the week.

The active weather pattern looks likely to continue through the
rest of the week and into next weekend. Another week low is
modeled to move into the OR waters on Wed, which may bring some
small craft advisory winds. Then there is potential for a
stronger system late in the week or early next weekend. Pyle

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning until 4 AM PST Tuesday for Central Oregon
     Coast-North Oregon Coast.

WA...High Wind Warning until 4 AM PST Tuesday for South Washington
     Coast.

PZ...Gale Warning until 4 AM PST Tuesday for Coastal Waters from
     Cape Shoalwater WA to Florence OR out 60 NM.

     Small Craft Advisory for Rough Columbia River Bar until
     10 PM PST Tuesday.

&&

Interact with us via social media:
www.facebook.com/NWSPortland
www.twitter.com/NWSPortland

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.