978
FXUS66 KPQR 132255
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
355 PM PDT Fri Sep 13 2024

.SYNOPSIS...A fall-like weather pattern will continue through next
week with mild days and cooler nights. Chances for light showers
return tonight through Sunday afternoon as an upper level trough
moves into the Pacific Northwest. By Sunday evening, conditions
dry out as the system moves into California. The next stronger
frontal system will bring widespread rain and more significant
rain totals to all of NW Oregon and SW Washington Tuesday into
Wednesday.

&&

.SHORT TERM...Friday night to Sunday...Shortwave ridging
overhead will continue to bring pleasant weather across NW
Oregon and SW Washington for the reminder of the day. Afternoon
highs remain forecast in the low to mid 70s for interior valleys
and 60s along the coast. Expect high pressure to weaken this
evening as a shortwave trough approaches western Washington.
This will lead to a gradual increase in mid to high level cloud
cover from north to south, along with a return for light shower
chances. Most areas have a 15-30% chance of showers through
tomorrow (Saturday) morning, but the best chances (40-60%) will
be in the along the north OR/south WA coast, north OR Coast
Range, and Willapa Hills.

Saturday afternoon, the upper level trough will dip further
south, spreading shower chances further south and inland.
Generally expect a 20-50% chance of PoPs across NW Oregon, with
higher PoPs around 60-80% at times over parts of SW Washington
(east of the Cascades). 24 hour forecast precipitation amounts
ending 11 PM Saturday are very light: generally less than 0.10
inch across NW Oregon and 0.10-0.25 inch across SW Washington.
Areas south of Salem could be completely dry on Saturday.

Saturday night into Sunday, the upper trough dips further south.
A few post-frontal showers continue, but expect conditions to be
mostly dry at this point, especially north of Salem given the
track of the low. Shower activity will gradually decrease from
north to south, with very little additional precip.    -Alviz

&&

.LONG TERM...Sunday night through Thursday...Mainly dry
conditions on Monday as the low shifts into northern California
and Nevada, bringing northeast flow aloft to western Oregon and
SW Washington. Models suggest a good deal of sunshine, allowing
temps to warm into the mid 70s for the interior lowland valleys
and 60s at the coast.

Conditions will deteriorate quickly on Tuesday as a stronger
frontal system brings more significant moisture into the region.
Confidence is very high widespread rain will occur across all
of western WA/OR during that time as every single ensemble
member from the GEFS/GEPS/ENS are showing QPF and NBM PoPs are
over 90%. Despite high confidence for rainy conditions,
confidence is lower in regards to exact rain amounts. There is
still a large degree of model spread for QPF, however ensemble
member clustering is evident between 0.25-0.75 inches for the
lowlands. The latest NBM probabilities also support significant
rain amounts with a 70-80% chance for 24-hr rain amounts in
excess of 0.50 inch. This means a soaking rain capable of
putting a serious damper on wildfire activity is very likely to
occur. This system will also bring temps around 10-15 degrees
below average for this time of year with highs likely in the low
to mid 60s on Tuesday.

Expect post-frontal showers on Wednesday with conditions mostly
drying out by Thursday. From there, temperatures will rebound to
near seasonal averages for interior lowland valleys.  -Alviz/TK

&&

.AVIATION...West flow aloft, with increasing mid and high clouds
this afternoon into tonight. Few showers along the coast, with
increasing MVFR along the coast tonight. MVFR with patchy IFR
along the coast tonight will persist into Sat am, thanks to
moderate onshore flow. Should remain VFR inland overnight, though
CIGS gradually lowering to near 4000 ft late tonight.

PDX APPROACHES...VFR with increasing mid and high clouds for rest
of today into tonight. May see a few light showers overnight, but
flight conditions remain VFR, though CIGS will gradually lower to
near 4500 to 6000 ft overnight.                   /Rockey

&&

.MARINE...Little change. Weakening front on the waters will push
inland tonight and Saturday. Low pressure will remain over the
waters on Sat, then shift southward and move into northern Calif
through Sun. But, pressure gradients remain on lighter side, with
winds 15 kt or less. Seas stay in 3 to 6 ft range.

High pressure builds a back across the WA/OR waters Sun and Mon.
But that temporary, as rather strong front will push across the
region Tue. Some potential for south wind gusts of 25 to 35 kt at
that time, with boost in seas to near 10 ft. But, will see how
things shape up as get closer in time to next Tue.     /Rockey

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...None.

&&

$$

www.weather.gov/portland

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