812
FXUS66 KPQR 160452
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
952 PM PDT Sun Sep 15 2024

.UPDATED AVIATION DISCUSSION...

&&

.SYNOPSIS...
A fall-like weather pattern will continue over the
next week. Dry weather expected tomorrow (Monday) with sunshine
and warmer temperatures. Rapid change to cool and wet conditions
Tuesday into Wednesday as a strong frontal system brings widespread
rain to the area. Drier and warmer conditions Thursday and Friday,
with more widespread precipitation chances returning Saturday.

&&

.SHORT TERM...Now through Tuesday night...Radar, satellite, and
surface observations as of 230 PM PDT depict dry weather across
the region with broken cloud cover as an elongated upper trough
moves southward toward California. There remains a 25-50%
chance of showers in the Linn and Lane County Cascades through
the early evening, but the vast majority of places will stay dry
through tonight. The upper trough will eventually become a cut-
off low tonight and spin over California/Nevada. Flow aloft
will turn more northeasterly and lead to some light offshore
flow in the high Cascades overnight. Everywhere else, winds will
be light and variable with mostly clear skies for most places.
Tonight`s lows are forecast in the upper 40s to low 50s, except
upper 30s to 40s in the Cascades.

Monday will be the sunniest and warmest day of the week as high
pressure aloft briefly returns over the region. Conditions will
be dry with afternoon highs forecast in the mid to upper 70s
for interior lowlands and mid to upper 60s along the coast.
Still can`t rule out temps reaching 80 for the Willamette Valley
as NBM suggests a 15-30% chance of high temps of 80 degrees or
warmer from Eugene to Portland. Overall, Monday will be a great
day for outdoor activities before the next frontal system
arrives and brings more unsettled weather.

Monday night into Tuesday, a frontal system will arrive and
bring widespread rain. In terms of timing, the front begins to
approach northwest Oregon and southwest Washington after 11 PM
Monday. At this point, winds will begin to shift more southerly
and be breezy at times. Precipitation chances reach the coast
after 5 AM Tuesday and spread inland through the morning. Based
on high resolution models, rain will reach the Willamette
Valley, Portland/Vancouver Metro, and Cowlitz Valley by late
morning Tuesday. 24 hour rain totals ending 5 AM Wednesday are
forecast around 0.35-0.70 inch for interior lowland valleys,
except less than 0.25 inch closer to the central Columbia River
Gorge and Upper Hood River Valley. Along the coast, Coast Range,
and Cascades, 24 hour rain totals are forecast around 0.50-0.80
inch, with locally higher amounts up to 1 inch on the west
slopes of the Coast Range.

Probabilities for 24 hour rain amounts over 1 inch ending 5 AM
Wednesday are around 10-25% for lowlands between Kelso and
Corvallis. Probabilities increase to around 30-50% along the I-5
corridor from Junction City to Cottage Grove. 40-60% chance
along the coast and Coast Range, and a 30-50% chance in the
Cascades. Regardless of exact rain amounts, enough will fall to
result in a significant damper on fire activity. Temps will also
fall 10-15 degrees below normal on Tuesday, with highs struggling
to rise above the low 60s for lowland areas and 50s in the
Cascades.      -Alviz


.LONG TERM...Wednesday through Saturday...Ensemble guidance
suggests that the upper level trough associated with Tuesday`s
rain will exit southward toward California on Wednesday. Expect
some post-frontal showers Wednesday morning, but shower chances
will quickly diminish by the afternoon as weak high pressure re-
builds. Model soundings also suggest decreasing clouds on
Wednesday, so temps will rebound to the upper 60s and low 70s.
Expect similar temps Thursday through Saturday. Most ensemble
guidance depicts shortwave ridging late in the week (Thursday to
Friday), resulting in dry conditions. However, there is a bit
more uncertainty on Saturday as about 55% of ensemble members
from WPC cluster analysis depicts troughing returning to the
region. If this occurs, cooler and wetter weather would return
this weekend. For now, the current forecast includes NBM`s
20-40% chance of PoPs going into Saturday. -Alviz

&&

.AVIATION...Overall expect generally VFR conditions going through
the TAF period. While intermittent cloud cover passes overhead
tonight, temperatures do not appear to lower enough for fog to be
a concern across the Willamette Valley come sunrise Monday
morning. However, the coast is one location that would be
potentially prone to a brief period of stratus, especially near
KONP, between roughly 12-15z. High pressure continues to build on
Monday keeping VFR cigs/vis in place with no concerns midday
through the afternoon.

PDX APPROACHES...General VFR through the next 24 hours although
a layer of FEW-SCT at 1.5kft may materialize right around sunrise
- only a 20% chance to see conditions drop to MVFR or lower
during this 13-16z early morning period. Winds may become breezy
in the late afternoon, but gusts not expected to exceed 15 kt.
-Schuldt

&&

.MARINE...
High pressure over the outer waters will build tonight
into Sunday. As such, will maintain the northerly pressure
gradients, with gusty north winds Sunday night. Small Craft
Advisory continues for late this afternoon into Monday, where
have gusts 20 to 25 kt. Have extended this advisory into the
northern outer waters (PZZ271) for the same time period as seas
will increase and, when combined with the winds sitting on the
marginal side of thresholds, would prompt this advisory. Will note
that conditions have been slow to respond today so it is possible
that it will take a bit longer for buoys to show these conditions.
However, nearshore observations inland are showing gusts up to 20
kt. Will continue to monitor at this point. Overall, seas stay in
5 to 8 ft through Monday, with highest seas well offshore.

On Tuesday we will see yet another pattern shift as a
strengthening low pressure system drops down from British
Columbia. By time it reaches the waters, it will elongate/weaken.
Winds not really turning to southerly (as do with most fronts),
but may briefly get burst of west to southwest winds of 20 to 25
kt with the frontal passage. Models still vary some on the
timing/strength of this system, so will see how things shape up as
get closer in time to Tuesday. -Muessle/MH

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 11 AM PDT Monday for PZZ252-253.
     Small Craft Advisory until 11 PM PDT Monday for PZZ271>273.
&&

$$

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