High Wind in Washington, January 27, 2018

Area Forecast Discussion
National Weather Service Portland OR
815 PM PST Fri Jan 26 2018

.SYNOPSIS...A low pressure system off the Pacific will move NE
towards Vancouver Island tonight and early Saturday. This system will
provide a burst of gusty winds to the coast tonight and early
Saturday as well as a round of moderate to heavy rain and Cascade
snow for Southwest Washington and Northwest Oregon. Another low
further west will brush a warm front across the area Saturday night
and Sunday morning for light rain and rising snow levels. Dry and
mild weather is expected Sunday afternoon through Monday afternoon. A
cold front will bring a return of rain Monday evening through Tuesday
morning. Lowering snow levels and showers are likely on Tuesday.

&&

.UPDATE...Updated WSW by adding timing of heaviest snowfall -
midnight to 6 AM Sat - for the Cascades as a warm and cold front
moves through. Precipitation decreases Sat morning as the snow level
rise to near or above Cascade passes.  /mh

.SHORT TERM...Tonight through Monday...Moist onshore flow is
maintaining showers across the region this afternoon and evening with
snow levels around 3000 feet. A low pressure system currently near
44N 138W (~450 miles offshore) will deepen as it nears the Washington
coast this evening. A moist front will bring a period of heavy rain
and Cascade snow to the region tonight through Saturday morning.
Another 0.75 to an inch of rain is likely for the coast, coast range,
and the Cascade foothills (below 2500 feet) tonight through Saturday
morning. Around a half of an inch of rain is possible for the
interior low lands including the Willamette Valley. Rain will turn to
showers behind the front by Saturday afternoon, and snow levels will
rise to above the Cascade passes early Saturday evening.

Coastal winds will increase tonight as the low nears, with a burst of
gusty winds overnight tonight into Saturday morning. The wind gusts
should remain just under the high wind warning criteria (58 mph).

Another low approaches Saturday night, but will remain further west
and lift further north than the first low.  This second low will
bring the tail end of a warm front across NW Oregon and SW Washington
Saturday night into Sunday morning continuing showers. The rain will
end south to north late Sunday morning through the early afternoon.
SW Washington and NW Oregon will be mostly dry Sunday afternoon
through Monday morning as a moist cold front stalls nw of the region.
The interior valley temperatures will warm into the mid to upper 50s
Sunday afternoon which is around 10 degrees warmer than the seasonal
normals.

Snow levels will remain above the Cascade passes Monday afternoon as
the cold front begins to make its way south across SW Washington and
NW Oregon. ~TJ

.LONG TERM...Monday night through Friday. A moist cold front will
move across the region Monday night. An upper trough will support
showers Tuesday and possibly Wednesday with snow levels around 2500
feet. AN upper ridge builds over the NE Pacific Wednesday or Thursday
providing potential for drier weather late in the week. There is
model disagreement on where this ridge will set up with vast
differences in whether the weather will be dry or showery Wednesday
through Friday. ~TJ

&&

.AVIATION...Warm front approaching from the west. As of 8 pm,
warm front was about 80 miles offshore. As it approaches, will
see rain increasing across region between 05Z and 08Z, along with
increasing MVFR conditions. Snow levels stay low, with vis
limited due to increasing snow above 3500 ft MSL.

Gusty southerly winds will increase along the south and central
coastal areas of Oregon after 07Z, with gusts 35 to 45 kt. Said
winds will spread up the coast overnight.

Cold front farther offshore will overrun the warm front later
tonight, shifting onshore between 14Z and 16Z Sat. This will
bring transition of rain to showers at that time. Still, plenty
of MVFR conditions across the region Sat am, with higher terrain
obscured. Overall, will keep mostly VFR with some MVFR due to
showers for rest of Sat.			     /Johnson

PDX AND APPROACHES...Generally VFR this evening, then increasing
MVFR as rain increases between 06Z and 09Z. Moderate threat
for low level wind shear later tonight, as will have moderate
southerly winds just aloft. Between 12Z and 14Z, gusty south
winds will finally reach field level, with gusts to 30 kt. Winds
ease back later Sat am, but will maintain mix of MVFR and low VFR
through most of the day, with scattered showers.    /Johnson

&&

.MARINE...A 997 mb low pres now sits about 400 miles to west of
Newport. Models fairly good agreement with this low deepening a
tad more tonight as it tracks northeastward towards Vancouver
Island. A warm front extends from the this low to east and
southeast towards the Calif/Ore boarder. Based on buoy data,
appears warm front now sits just east of bouy 89, or roughly 80
miles offshore. NOAA satellite imagery and data indicating broad
area of gusty southerly gales along and behind the warm front.
Models consistent in bring the warm northward this evening, but
cold front will catch up with the front later tonight, with
resulting occluded front pushing across the coastal waters late
tonight and onshore early Sat am. Strongest winds will be off the
Oregon coast between 11 pm and 4 am.

Bottom line, southerly gales now developing across the outer
waters. Winds will crank up a bit more on the outer waters
tonight, with storm force gusts of 45 to 50 kt for a time on the
outer waters south of Cascade Head. Current marine warning
remain unchanged.

Seas currently 11 to 13 ft, but these will build quickly as winds
increase. Still reasonable to expect seas building to 17 to 22
ft overnight, with higher seas on the outer waters. Though wind
wave energy subsides on Sat am, will have to deal with bigger
baseline swell of 16 to 18 ft through the afternoon.

Another weak front will lift north across the region Sat night,
but this front sits to our north for Sun and Mon. Later Mon and
mainly Mon night, the frontal boundary will sag back over our
region, with marginal southerly gales.		 /Johnson

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 6 AM PST Saturday for Upper Hood
     River Valley.

     Winter Weather Advisory until 10 AM PST Saturday for Cascades
     in Lane County-Northern Oregon Cascades.

WA...Winter Weather Advisory until 10 AM PST Saturday for South
     Washington Cascades.

     Winter Weather Advisory until 4 AM PST Saturday for South
     Washington Cascade Foothills.

PZ...Gale Warning until 10 AM Saturday for all coastal waters.

     Storm Warning until 6 AM Saturday for Waters from Cascade Head
	to Florence, from 10 to 60 NM.

     Small Craft Advisory for Rough Columbia River Bar conditions
	for tonight through Sat afternoon.

&&

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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.