446
FXUS66 KPQR 180441 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
941 PM PDT Tue Sep 17 2024

Updated short term and aviation discussions.


.SYNOPSIS...A weak frontal system will continue to bring
clouds, cool temps, and light rain showers overnight. Dry
weather returns Wednesday through Friday with onshore flow and
slightly below normal temps. Rain potential returns this
weekend, but confidence is low in the overall pattern.

&&

.SHORT TERM...Now through Thursday Night...Radar is showing the
showers moving through the area but are currently concentrated
more to the southern portions of the forecast area. Satellite
shows a weak meso-low along the coast, with the main low
pressure system (that is the weather maker) sits right over the
OR/CA border. Expect light rain showers to gradually move
over the area through the night. Precipitation amounts are
forecast to be very light as models suggest the track of the
upper trough will be slightly offshore and moving southward,
minimizing rainfall amounts across northwest Oregon and
southwest Washington. The highest forecast amounts are are
around 0.10-0.40 inch, generally south of a line from Tillamook
to Oakridge. Northward, expect less than 0.10 inch of rain.
Winds will also be from the south/southwest, with the strongest
gusts (25-30 mph) through the central Columbia River Gorge and
over the Cascade crest.

Tonight into tomorrow (Wednesday), the upper level trough will
exit our area and continue moving into California. High pressure
will re-build as a positively-tilted ridge noses into the region
from the Pacific. Winds will gradually weaken and shift back to
a north/northwest direction. Expect decreasing PoPs and a return
to dry conditions. Will also see decreasing cloud cover overnight,
so some locations could see patchy fog development given the
moist conditions and calm winds. HREF currently suggests spotty
chances (10-30%) of visibility falling below 1/2 mile for
locations east of the Cascades. Otherwise, expect a mostly
sunny day tomorrow with high temperatures rebounding to the low
to mid 70s for interior lowland valleys and mid 60s along the
coast. Thursday remains benign as high pressure lingers, with
continued onshore flow and similar high temperatures as
Wednesday.      -Muessle/Alviz


.LONG TERM...Friday through Tuesday...
Friday through Tuesday...Friday looks to be another
warm and pleasant September day characterized by increasing
onshore flow as a positively tilted ridge axis slowly shifts
south of the region. Expect temperatures slightly below seasonal
norms with inland highs in the low 70s. Forecast confidence
remains below normal this weekend into the early part of next
week as model solutions continue to diverge significantly with
regard to how the upper level pattern will evolve beyond Friday.
Ensemble clusters remain just about evenly split in depicting
ridging, troughing, and zonal flow regimes over the Pacific
Northwest from Saturday through Monday. This obviously will have
large implications for the forecast as anything ranging from
warm and dry weather to a cooler and wetter pattern remains on
the table for days 5-7. This continues to be reflected in the
NBM interquartile ranges for temperatures which range anywhere
from the upper 60s to the upper 70s between the 25th and 75th
percentile guidance. As such, and until models begin to converge
on a solution, have opted to stick with the NBM mean which
splits the difference between these solutions and depicts broad-
brushed chance to slight chance PoPs over the area late this
weekend through early next week.   -CB

&&

.AVIATION...An upper level low over the Oregon coast will drop
south tonight toward the northern CA coast, resulting in southeast
flow aloft shifting to the northeast by Wednesday morning. Light
rain will gradually dissipate this evening, with widespread MVFR
stratus settling in across the area, with higher chances of IFR
along the central Oregon coast. Probability of conditions
improving to VFR increase late Wednesday morning to early
afternoon around 18-20z. Winds become light and variable
overnight, becoming northwest by Wed afternoon.

PDX APPROACHES...Light rain should dissipate by 06z while MVFR
stratus expected to settle in with CIGs around 1500 ft through
late Wed morning. Expect conditions to improve to VFR after 18-19z
Wed. Winds becoming light and variable overnight, before becoming
northwest 6-8 kt by Wed afternoon. -DH

&&

.MARINE...
A weather system drops down from British Columbia
tonight into Wednesday. However by the time it reaches the
waters, it will elongate and weaken. Winds have shifted southerly
as the front nears. Peak wind gusts up to 15 kt along the coastal
waters will relax tonight as the system falls apart. There is a
slight chance for thunderstorms tonight primarily over the outer
zones.

Northerly winds return Wednesday as high pressure rebuilds offshore.
Winds may gust 20 to 25 kt at times, primarily over the outer
zones. Seas around 4 to 6 ft today and tonight, increasing to
around 8 ft later Wednesday into Thursday, then settling to around
5 ft late in the week.      -Hall/mh

&&

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

$$

www.weather.gov/portland

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