High Wind in Oregon, January 11, 2018

Area Forecast Discussion
National Weather Service Portland OR
312 AM PST Thu Jan 11 2018

.SYNOPSIS...A strong low pressure system will move through the
Pacific Northwest today, with brisk winds and heavy rain today
turning to showers later today and tonight and with snow in the
Cascades tonight. Showers linger into Friday. A weak system brushes
the area especially along the coast and in the north interior Friday
night before higher pressure and offshore flow develop this weekend,
though there will be some fog away from the Columbia River Gorge. A
series of fairly strong Pacific frontal systems will affect the
forecast area next week, with the first one late Monday into Tuesday,
another Wednesday, and more late next week.
&&

.SHORT TERM...Today through Saturday...The models all show a strong
low pressure system moving through the Pacific Northwest today. The
warm front with this system is spreading in early this morning,
followed by the cold front mid day. The cold front looks to move
onshore along the coast between 10 am and noon today, and through the
inland areas in the early to mid afternoon. The associated surface
low is forecast to move onshore across the Olympic Peninsula at
around 1000 mb. It looks like it will be windy south of the low, with
gusts to 60 mph or so along our coastal beaches and headlands, to 45
to 50 mph in the coastal communities and in the higher terrain of the
coastal mountains and the Cascades, and to around 40 mph in the
valleys. With leaves off the trees, there should be less problems
with 40 mph wind gusts in the valleys than in October or November,
but a few issues are always possible with these speeds.

Rainfall amounts are another issue. QPF values through tonight could
reach 2-4 inches along the coast, in the coastal mountains, and in
the Cascades, with the heaviest in the north. Valley amounts of
0.5-1.5 inches are possible. Right now river flooding is not forecast
though sharp rises are expected. If any river can reach flood stage,
it will be the Grays River in Wahkiakum County, though we will need
to watch some other coastal rivers as well.

There is a lot of onshore flow behind the front around the southern
periphery of the surface low, and we should see plenty of
post-frontal showers later today and tonight. Snow levels drop to
around 4500 feet in the Cascades tonight, and snow amounts in the 4
to 8 inch range with locally higher amounts at ski resort levels are
possible tonight and early Friday. Have issued a snow advisory for
the south Washington and north Oregon Cascades for this.

Some showers continue through Friday though amounts and coverage will
decrease as the onshore flow eases. An upper ridge then starts to
develop, though our area gets brushed by a system Friday night with a
little bit of rain along the coast and in the north interior area
before the upper ridge fully takes hold Saturday.

East winds develop Saturday, but this is largely a gap wind event
through the Gorge. There is blocked flow in the remainder of the
valley areas, which means that there will probably be some fog that
develops especially in the south and central Willamette Valley Friday
night that will be slow to dissipate Saturday. Tolleson

.LONG TERM...Saturday night through Wednesday...The models are
showing a pattern change next week when compared to the last week or
so with a more zonal pattern setting up. A series of fairly strong
lows move through, and the GFS and ECMWF are in better agreement with
the details early this morning.After the dry weather of this weekend,
the first system is expected late Monday into Tuesday, with another
around Wednesday, and another later in the week. One or more of these
lows could be quite strong. Tolleson
&&

.AVIATION...MVFR cigs and vis prevailing today with occasional IFR
conditions as a warm front lifts across the area this morning. May
see some improvement as the warm front departs the area.  Winds will
increase following the warm front with coastal areas seeing gusts 40
to 50 kt and inland 25 to 35 kt. A cold front moves to the coast by
midday and inland shortly after with mostly MVFR conditions. Winds
remain elevated until the associated low moves inland late afternoon
and evening.

PDX AND APPROACHES...MVFR cigs and vis prevailing after 12Z and into
late afternoon. May see IFR conditions 14Z-18Z with the warm front
moving through the area. While MVFR will probably continue into this
evening, rain shadowing may develop over the area in the evening for
possible VFR conditions.  Gusty south winds 25 to to 35 kt 15Z thru
03Z Fri.  /mh
&&

.MARINE...South winds increasing this morning reaching gales by
sunrise. Expect widespread gale force winds mainly during the
daylight hours, with a gradual weakening in winds in the evening. The
northern part of the waters will be most susceptible to gales
lingering into the evening as a surface low tracks east towards the
Olympic Peninsula late in the afternoon. The bent-back occlusion
associated with the low can easily surface stronger winds from aloft
and may affect the south Washington and north Oregon waters. Models
show winds at 850 mb and below weakening during the time this feature
would affect the waters late afternoon and early evening so it may be
weaker than earlier anticipated.

A combination of an increasing westerly swell and the increased winds
will quickly build seas today, likely topping out between 18 to 21 ft
from mid afternoon until evening. The higher seas should slowly
subside late tonight and Fri, likely going below 10 ft Fri night.

A warm front brushing across the northern water late Fri brings a
chance for winds gusting into the 20 to 25 kt range late fri night,
but otherwise expect winds under 20 kt through Sat. Another frontal
system arrive late Sun and Mon bringing the next likelihood of small
craft winds, if not low end gales.
&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning from 8 AM this morning to 5 PM PST this
     afternoon for Central Oregon Coast-North Oregon Coast.

     Winter Weather Advisory from 4 PM this afternoon to 7 AM PST
     Friday for Northern Oregon Cascades.

WA...High Wind Warning from 8 AM this morning to 5 PM PST this
     afternoon for South Washington Coast.

     Winter Weather Advisory from 4 PM this afternoon to 7 AM PST
     Friday for South Washington Cascades.

PZ...Gale Warning until 10 PM PST this evening for Coastal Waters
     from Cape Shoalwater WA to Cascade Head OR out 60 NM.

     Gale Warning until 6 PM PST this evening for Coastal Waters
     from Cascade Head OR to Florence OR out 60 NM.

     Small Craft Advisory for Rough Columbia River Bar until 6 AM
     PST Friday.

&&

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 CWA, or forecast area.