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Area forecast discussion 
National Weather Service Portland or
155 PM PST Sat Feb 28 2015

Synopsis...a deep upper trough continues to dig southward into
California...with high pressure settling into the Pacific northwest
behind it. Dry northerly flow will lead to plenty of sunshine this
weekend...with seasonably cool nights and afternoon temperatures in
the 50s for The Lowlands. A weaker upper trough will dig down the
British Columbia coast Sunday...with increasing high clouds later
Sunday. Some light rain and mountain snow will be possible Sunday
night and Monday...with snow levels as low as the foothills. However
any snow accumulations should be very light. Another dry spell is
expected thereafter as another strong high pressure system builds
over the region for much of the coming week.

&&

Short term...tonight through Tuesday...skies are Crystal clear
across the forecast area this afternoon...as dry and somewhat
blustery northerly flow takes over. The upper level trough which
brought yesterdays shower activity has since moved southward into
California...with high pressure strengthening over the Pacific
northwest. Dewpoints have dropped into the 20s and lower 30s most
areas. Clear skies and decreasing wind should allow temperatures to fall
below freezing tonight for most of the outlying valleys...while urban
areas hover near or just above freezing. Some patchy fog is possible
in sheltered valleys tonight and Sunday morning due to near ideal
radiational cooling conditions. Aside from the patchy fog...Sunday
should be mostly sunny due to high pressure...though some high
clouds ahead of our next system may work their way in by the end of
the day.

Water vapor satellite imagery shows an upper level trough moving
through Alaska...this system will eventually split into two pieces.
The northern portion will be the stronger of the two...and is
expected to slide down the Canadian rockies and emerge as an Alberta
clipper in the northern Great Plains. The weaker western system will
slide down the British Columbia coast...eventually bringing another
chance of precipitation to our forecast area Sunday night and Monday.
Most models now show this western system to be in a bit of a hurry to
join the more dominant upper trough over California... guided by a
100 kt+ northerly jet. As a result this system will be a fast mover
and quantitative precipitation forecast will be light. NAM bufr soundings continue to indicate some
pretty low freezing levels as precipitation tries to move in Sun night/early
Monday...so the foothills above 1500-2000 feet may get a light dusting of
snow by Monday morning.

Drier weather will be quick to return as another strong high pressure
system builds down from western Canada. Monday night should be
another dry and chilly night with subfreezing temperatures in the outlying
valleys. Tuesday should see plenty of sunshine with seasonable
temperatures as high pressure and dry northerly flow return. Weagle

Long term...Tuesday night through Saturday...extended forecast
models continue to show March coming in like a Lamb for the Pacific
northwest. The mean upper ridge position lingers where it has been
much of this winter...over the NE Pacific and along the West Coast.
This should keep the Pacific jet stream well to our north...as well
as any chances of significant precipitation. Removed mention of any
rain from the forecast Tuesday through Saturday. Conditions may
become increasingly favorable for fog in the valleys...as most
guidance pushes the upper ridge axis onshore late in the week.
Otherwise expect a gradual return to above normal temperatures which
may last into next weekend. Weagle

&&

Aviation...VFR conditions prevail today. As low pressure over north
California slides off to the south and east...gusty northeast
winds across the area will start to subside this evening. This
will allow some patchy fog to develop in the Willamette Valley
overnight...which could affect inland sites bringing ceilings and visible
down to IFR/LIFR. Kpdx and kttd should remain VFR overnight
because the dry east wind out of The Gorge will persist
overnight...though not as strong as this afternoon. Coastal sites
should remain VFR overnight as well under dry offshore flow.

Kpdx and approaches...VFR conditions with gusty east winds up to
20 knots this afternoon. Winds should start to subside a bit this
evening but continued dry east winds will keep fog from
developing. VFR conditions expected to persist overnight into
Sunday morning. -McCoy

&&

Marine...low pressure over north California will continue sliding off to
the south and east...which will allow winds to drop back down
below small craft criteria tonight. The next system forecast to
move through Sunday night into Monday is looking a bit stronger
with new model runs in each the NAM...GFS...and European model (ecmwf). This has
given confidence that a Small Craft Advisory for winds is needed
for the outer waters starting early Monday morning. Winds drop
back below small craft criteria over the northern outer waters
late morning Monday...while winds persist over the southern outer
waters until late Monday night. Seas with this system will come
back up in the outer waters a bit...getting up to 8 feet with the
winds...but look to stay below 10 feet at this time. We will monitor
this for the possibility of square seas with periods still around
8 seconds.

High pressure builds back over the NE Pacific behind the Sunday
night/Monday system and remains in place through the work
week...keeping winds and seas fairly benign. -McCoy

&&

Pqr watches/warnings/advisories...
or...none.
Washington...none.
Pz...Small Craft Advisory for winds until 3 PM PST this afternoon
for waters from Cape Shoalwater Washington to Cascade Head or from 10
to 60 nm.

Small Craft Advisory for winds from 1 am to 10 am PST Monday
for waters from Cape Shoalwater Washington to Cascade Head or from 10
to 60 nm.

Small Craft Advisory for winds until 9 PM PST this evening for
waters from Cascade Head to Florence or from 10 to 60 nm.

Small Craft Advisory for winds from 1 am to 10 PM PST Monday for
waters from Cascade Head to Florence or from 10 to 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.

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