Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 251055
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
254 AM PST Tue Feb 25 2020

.SYNOPSIS...Clear skies overnight will result in a cool start to the
day. Clouds will increase later today as a weakening front nears.
Light rain or drizzle is expected across southwest Washington and
extreme northwest Oregon tonight as the front moves inland. High
pressure returns dry weather Thursday and Friday, with mild daytime
temperatures and cool nights. A slightly stronger front is expected
Friday night and Saturday for another chance of rain and mountain
snow.

&&

.SHORT TERM...Today through Thursday night...Satellite imagery shows
mostly clear skies early this morning with high pressure aloft. The
clear skies and light surface winds has resulted in radiation cooling
with widespread temperatures in the lower to mid 30s. Patchy
fog/freezing fog is possible in some of the interior valleys early
this morning. Clouds will increase from north to south later today as
a weak frontal system approaches.

The front decays as it moves across extreme SW Washington and NW
Oregon late this afternoon and evening. This feature may produce
light rain or drizzle across SW Washington and parts of extreme NW
Oregon this evening and tonight with little to know accumulation.
Light onshore flow and cloudy skies will limit cooling overnight
tonight and expect temperatures in the upper 30s to lower 40s early
Wednesday.

High pressure builds Wednesday night into Thursday for clearing
skies, cooler overnight temperatures, and patchy valley fog. A
thermal trough of low pressure over NW California spreads north along
the Oregon Coast Thu morning for light offshore winds. Models
forecast 850mb temperatures of +7C south of Salem Thursday afternoon
which may result in afternoon temperatures close to 60 deg F for the
interior valleys. The thermal trough remains along the Oregon coast
Thursday night, but slightly weaker. ~TJ

.LONG TERM...Friday through Sunday...Weak high pressure remains
positioned over the Pacific Northwest on Friday for continued dry
weather and partly to mostly sunny skies. Day time heating will
result in spring-like temperatures Friday afternoon with many
locations likely peaking in the lower 60s. Another front will return
the chance for rain and Cascade snow Friday night and Saturday. A low
pressure system will move across the NE Pacific towards the Oregon
coast on Saturday. The models are trending that a splitting upper
trough will keep the low offshore of Oregon as it passes south
Saturday night and Sunday. This low still has the potential to
generate precipitation as it brushes by this weekend, especially if
the northern energy of the splitting trough moves across NW Oregon.
~TJ

&&

.AVIATION...VFR prevailing today but with stable conditions and
light offshore flow, pockets of fog and stratus have developed
mainly in the valleys of the coast range and Cascade foothills.
Fog over the lower Columbia River near KKLS may expand up river
to near the Portland/Vancouver area this morning. Also fog may
develop in the Tualatin valley for a few hours this morning
affecting KHIO. An approaching front will bring increasing mid
and high level clouds this afternoon and tonight with MVFR cigs
reaching the coast this evening.

KPDX AND APPROACHES...VFR prevailing today and tonight. However
with fog in the KKLS area may expand up river and approach the
area. Current MOS guidance is not indicating fog for this
morning though with temperature - dew point spread around 3
degrees with no wind, should see some fog 14-16Z this morning.

&&

.MARINE...Winds and seas are below advisory criteria this
morning as a surface ridge of high pressure lay over the coastal
waters. A weakening front will brush the northern zones later
today and tonight for south to southwest winds over the northern
zones. A ridge of high pressure will again lay over the waters
with a thermal trough along the south Oregon coast. This will
result in west to northwest winds toward the WA waters and
northerly winds for the remainder of the area. North winds could
gust near 20 kt from Newport southward on Wed and Thu afternoon
and evenings.  Models are suggesting a stronger front will move
over the area this weekend, however at this point they are
depicting a splitting and weakening low pressure system. With
that in mind, there is a chance for another period of slightly
more active weather, however confidence remains low.
/mh

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...None.

&&
$$

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This discussion is for Northwest oregon and Southwest Washington
from the Cascade crest to 60 nm offshore. This area is commonly
referred to as the forecast area.


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