Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 201633
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
932 AM PDT Sun Aug 20 2017

.SYNOPSIS...Onshore flow will produce varying degrees of morning
clouds, afternoon sunshine. with inland temperatures in the 70s and
80s for much of the next week. Monday and Tuesday will likely be the
warmest days. A weak storm system will bring significant cooling and
could bring a few light showers to the forecast area late Wednesday
and Thursday before temperatures warm back to above seasonal normals
levels next weekend.
&&

.SHORT TERM...Today through Wednesday...Stratocumulus had trouble
forming this morning in southwest Washington and northwest Oregon as
the marine inversion has lowered a bit and because the air mass was
just not quite moist enough to develop the clouds despite the
continued onshore flow and the marine air mass across the area. The
only place that we can see any low clouds was along the south
Washington coast. Higher clouds associated with a weak disturbance
moving through Washington and southwest Canada will move across our
forecast area today and early tonight but we should still see plenty
of sunshine through the thin high clouds. Temperatures today will be
near or just above seasonal normals, with 80 to 85 common inland from
Vancouver southward.

Low clouds are solidifying off the coast this morning, largely due to
the passing weak upper disturbance, and these may increase a bit
along the coast today but will definitely push onto the south
Washington and north Oregon coasts tonight. The surface pressure
pattern suggests they will be less solid on the central coast around
Newport. The low clouds will likely push inland along the Columbia
River later tonight and early on Monday to Kelso with some clouds
trying to reach the Vancouver and Portland areas. Believe the clouds
in the Vancouver and Portland area will mainly be scattered before
mostly clearing before the main part of the eclipse. Farther
southward in the Willamette Valley conditions will stay mostly clear
for the eclipse on Monday morning. Some smoke from fires in the
Oregon Cascades could drift west on Monday but this will be slow to
occur and probably not affect eclipse viewing.

Otherwise Monday afternoon will be sunny as the morning clouds clear
to a little ways off the coast under a building upper ridge. The air
mass will be warming, and coastal temps could reach the lower 70s in
areas, with upper 80s and lowers 90s common inland except mid 80s
near Kelso.

The upper ridge starts to move off to the east Tuesday, but it is
still close enough for another warm day inland Tuesday with
temperatures in the mid 80s to around 90. We don`t expect much in the
way of lower clouds inland on Tuesday, though the coast will see
increasing lower clouds that may persist or hug the coastline much of
the day.

Southwest flow aloft will be increasing Tuesday night and Wednesday
as the upper ridge continues moving eastward and the next system
approaches. This will mean persistent cloud cover at the coast,
perhaps even some spotty drizzle, and more morning low clouds inland
with resultant cooler temps. Temperatures inland will likely be close
to or a bit below seasonal normals Wednesday.

Some convection late Tuesday spreading north from a weak low over
California might clip the Willamette Pass area, but southwest flow
aloft will limit any coverage and how far north it can reach in our
Cascades as it mainly spreads into central and eastern Oregon. The
approach of the system Wednesday is making any chance of convection
in that area looking less likely as the southwest flow aloft and the
low level onshore flow increases. Tolleson

.LONG TERM...No Changes. Previous discussion follows...
Wednesday night through Sunday...Models are in good agreement a
shortwave trough will slide eastward across British Columbia and
Washington Wednesday night and Thursday. This should bring cooler
temperatures, increased cloud cover and a chance of light rain,
particularly along the coast and across the Cascade foothills, but
even portions of the Willamette Valley could see some light rain.
Shortwave ridging should then build over the Pacific Northwest and
bring a return to more sunshine and above average temperatures
towards next weekend. /Neuman
&&

.AVIATION...VFR conditions coast and inland today. At 16z this
morning, there was a batch of stratus offshore from Astoria/Cape
Disappointment, but expect that to remain offshore today. Stratus
will move back into the north coast tonight after 04-06z with MVFR
and possibly IFR cigs.

KPDX AND APPROACHES...VFR conditions today and tonight. Marine
stratus will push part way up the Columbia River tonight to around
KLS.
&&

.MARINE...A persistent weather pattern will result in little change
in the marine weather the next several days. High pressure holds over
the NE Pacific while a thermal trough is along the south Oregon
coast. This supports north winds across the south Washington and
north Oregon waters. The thermal trough strengthens each afternoon
such that the north winds will increase and become gusty each
afternoon. The winds south of Cascade Head will have frequent gusts
to around 25 kt which supports the current small craft advisory for
winds.

The seas will be locally generated from these winds and generally
remain 4 to 6 ft with periods at 9 to 10 seconds. The seas will be
choppier in the southern waters for the afternoons with dominant
periods possibly around 8 seconds. tw/Bentley
&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for winds until 11 PM PDT Monday for
     Coastal Waters from Cascade Head OR to Florence OR out 60
     nm.

     Small Craft Advisory for Rough Columbia River Bar from 3 AM to
     7 AM PDT Monday.
&&

$$

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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 forecast area.


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