Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 200452
AFDPQR

Area Forecast Discussion
National Weather Service Portland Oregon
851 PM PST Thu Jan 19 2017

.SYNOPSIS...An upper level trough moving through southwest Washington
and northwest Oregon moved east of the area this evening. Another
system will push into the region late tonight and Friday and increase
the offshore low level flow. Winter weather will be possible again
in the Columbia River Gorge, Upper Hood River Valley, and the
Cascades. Additional waves of moisture will maintain the unsettled
weather over the area through this weekend into early next week,
with drier more seasonable weather returning next week.

&&

.SHORT TERM...Tonight through Sunday...The remaining piece of an
upper trough moved east of southwest Washington and northwest
Oregon this evening with decreasing but not quite ending showers.
Radar shows widely scattered showers over the coastal waters and
roughly the western half of the forecast area, but should be on the
increase later tonight.

East winds will increase tonight and Friday through the Columbia
River Gorge as the next low pressure system approaches, with
a 973-975 mb surface low setting up near buoy 5, 300 miles west of
Astoria. Easterly winds will pickup for somewhat breezy conditions
through the coast range and gaps leading to the coast, but the
gradient does not open up to expose the coast to strong winds since
the low position does not change too much and maintains the easterly
gradient.

The east winds will cause the precipitation to be cold rain
in the north valley areas Friday.  Model soundings show a trend
toward snow in the central and eastern Gorge areas on Friday. QPF
with this system is modest, with an inch or two of snow possible east
of about Multnomah Falls in the Gorge, and 1 to 3 inches in the
Cascades or the Upper Hood River Valley as the main band moves
through on Friday. There is some chance of freezing rain in the Gorge
and Upper Hood River Valley at the beginning of this event before
turning to all snow. Have issued a Winter Weather Advisory for Friday
for the Columbia River Gorge and the Upper Hood River Valley for a
good part of Friday. The Cascades will see some snow but below
advisory thresholds for that area.

Additional bands of precipitation are expected to rotate onshore
around the parent offshore low this weekend, with the next one on
Saturday midday. Look for more snow in the Gorge and Upper Hood River
Valley with cold rain in the north interior.

Another likely sub 970 mb sets up off the coast near bouy 5 again
Saturday night and Sunday, displacing the first low, and spreading
another band of precipitation onshore from the southwest late
Saturday night and Sunday. This looks like a repeat of Saturday with
cold rain in the northern valleys and snow in the Gorge and Upper
Hood River Valley.

Will need to monitor this weekend whether the east wind will be
strong enough to lower snow levels more than currently forecasted in
the northern valley areas. Sticking with the current forecast for now
but with only moderate at best confidence. Tolleson /mh

.LONG TERM...Sunday night through Thursday...A low pressure system
moves into the Northern California Coast early next week. As it
skirts the Oregon Coast Sunday night, will probably see windy
conditions mainly along Oregon`s Central Coast. Showers will be
decreasing on Monday, with a decent chance Monday is dry for most of
the area. Left a slight chance of showers, though, in the event this
system tracks a little farther north than currently forecast. Upper-
level ridge moves over the area midweek, bringing dry conditions and
offshore winds starting Tuesday and continuing into Wednesday. Next
chance of precipitation may be on Thursday with a weak shortwave
moving up into Vancouver Island, but confidence is very low at this
time. -McCoy
&&

.AVIATION...Isolated showers continue this evening, but will
generally taper off through about 07Z. Should see generally VFR
conditions but isolated MVFR in showers. An occluded front will
approach from the southwest later tonight and into Fri morning,
spreading steadier rain onshore from south to north from 12Z to
18Z Fri. Expect conditions will stay VFR over the interior, but
MVFR cigs are likely to develop at the coast during this time. The
approaching front will also restrengthen the offshore flow through
the Columbia River Gorge late tonight and Fri, bringing gusty
easterly winds back at KTTD and potentially at KPDX as well.

KPDX AND APPROACHES...Expect VFR to persist overnight through Fri
morning, but light rain likely increases again by around 15Z Fri
with possible MVFR cigs. Gusty easterly winds redevelop through
the gorge overnight and Fri, with gusts 20 to 25 kt likely
reaching near the terminal by mid-morning Fri. Bowen/Pyle

&&

.MARINE...A strong low pres system currently apparent on
satellite near 46N/145W will swing an extended occluded front
toward the Pac NW later tonight and Fri. This front will approach
from the southwest, and will lead to increasing SE winds. Due to a
significant easterly component to the flow, the most significant
impacts from this system will be over the outer waters, mainly
beyond 30 nm. Expect winds 25 to 30 kt with gusts to 40 kt. Winds
will drop off Fri afternoon and evening.

There will be another, likely much stronger system that impacts
the NE Pac over the weekend. The fcst models suggest that this
system will be fairly complex, with several low pres circulations
possible. However, they all seem to agree that there is likely to
be a sub-970 mb low that lingers over the NE Pac over the weekend
and into the early part of next week. This would mean significant
winds, likely storm force, in some areas around the low. However,
the exact timing and positioning of things is still in question.
At this time, it appears that the most significant impacts will be
to the south of our coastal waters, but will need to watch closely
over the coming days. The fcst models eventually move the low
south and onshore along the southern Oregon or northern California
coast sometimes late Mon or Tue.

Seas have begun to increase this evening as seen by observed 15 ft
at buoy 50. Increasing trend will continue tonight into Fri
morning with the next system, likely reaching near 20 ft over the
outer waters where the strongest winds are located. Seas will be a
bit lower over the nearshore waters. Then after a brief decrease
later Fri, expect a significant swell train to arrive late Fri
night into early Sat. Expect seas to build into the low to mid 20s
over the weekend. Much of the energy is westerly and long period,
so a high surf advisory will likely be needed as we get closer to
the event. Bowen/Pyle

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory from 5 AM to 4 PM PST Friday for
     Central Columbia River Gorge-Upper Hood River Valley-
     Western Columbia River Gorge.

WA...Winter Weather Advisory from 5 AM to 4 PM PST Friday for
     Central Columbia River Gorge-Western Columbia River Gorge.

PZ...Gale Warning until noon PST Friday for Waters from Cape
     Shoalwater WA to Florence OR from 10 to 60 nm.

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

     Small Craft Advisory for winds until noon PST Friday for
     Coastal Waters from Cape Shoalwater WA to Florence OR out
     10 nm.

     Small Craft Advisory for hazardous seas until 10 PM PST Friday
     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. The area is
commonly referred to as the forecast area.



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