382
FXUS66 KPQR 142223
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
323 PM PDT Sat Sep 14 2024

.SYNOPSIS...A fall-like weather pattern will continue over the
next week. Chances for light showers this weekend, however most
locations will be dry. Dry and mild conditions on Monday will
give way to cool and wet conditions Tuesday into Wednesday as a
strong frontal system brings widespread rain to the area. Drier
and warmer conditions return again late in the week.

&&

.SHORT TERM...Now through Monday night...Radar, satellite, and
surface observations as of 230 PM PDT depict broken cloud cover
across the area with scattered showers along the north OR/south
WA coast as a broad upper level trough dips southward from
British Columbia. As this trough continues to move south, expect
chances (15-40%) for light showers to continue across northwest
Oregon and southwest Washington. Any additional precipitation
through tomorrow morning will likely amount to less than a
tenth of an inch, with most locations remaining completely dry.

Tonight into tomorrow (Sunday), the upper level trough will
continue to elongate and move further south toward California.
At this point, it almost becomes a closed low. Conditions will
still remain mostly dry for us, though there will be some
spotty chances (15-40%) for showers tomorrow. The highest
chances of showers will be south of Salem and along higher
terrain of the central Oregon Coast Range and Cascades given
the track of this low. Afternoon highs are forecast to remain
slightly below normal, with low 70s for interior lowlands, low
to mid 60s along the coast, and 50s in the Cascades. By Sunday
evening/night, precipitation chances diminish as the upper
low completely exits the area.

Expect widespread dry conditions Monday through Monday night as
dry northeast flow aloft develops on the backside of the
aforementioned low. Monday is shaping up to be the sunniest and
warmest day of the week with high temps most likely in the mid
to upper 70s for interior lowlands and mid to upper 60s along
the coast. That said, cannot rule out temps a bit warmer than
that as the NBM is showing a 10-20% chance for high temps of 80
degrees or warmer within the Willamette Valley. Monday will be
an excellent day for outdoor activities, especially given the
rapid change to cool and wet weather expected the following day.
This system is discussed below in the long term discussion.
                                                   -Alviz/TK
&&

.LONG TERM...Tuesday through Friday...Conditions will deteriorate
quickly on Tuesday as a stronger frontal system brings more
significant moisture into the region. There is high confidence
for widespread rain, as every single member from the GEFS/GEPS/ENS
are showing QPF and NBM PoPs are over 90%. In terms of timing,
expect rain to begin early Tuesday morning and last through
early Wednesday morning before becoming more showery.

Despite the high confidence in rain occurring, there is still
uncertainty with exact rain amounts. The "driest" scenario
depicted by the 10th percentile NBM shows 24 hr QPF amounts
of 0.30-0.40 inch along the coast/Coast Range and 0.10-0.20 inch
east of the Coast Range, ending 5 AM Wednesday. The "wettest"
scenario depicted by the 90th percentile NBM shows 1.25-1.75
inches along the coast and mountains, and 0.75-1.25 inches for
interior lowland valleys. For now, the current forecast calls
for 0.40-0.60 inch in the Willamette Valley and 0.50-0.75 along
the coast and mountains.

NBM probabilities for a wetting rain (0.25 inch/12 hours) is
high (70-90%) across the region, so this system is capable of
putting a significant damper on wildfire activity regardless of
uncertainty on exact rain amounts. This system will also bring
temps around 10-15 degrees below normal for this time of year
with highs likely in the low to mid 60s on Tuesday.

Expect post-frontal showers on Wednesday with conditions drying
out Wednesday night into Thursday. Temperatures will rebound to
near seasonal averages for interior lowland valleys heading
into next weekend.      -Alviz/TK

&&

.AVIATION...West to northwest flow aloft, with considerable lower
and mid-level clouds today. Mix bag along the coast into Coast
Range, with widespread MVFR and IFR pockets. As weak front along the
coast moves further inland, will see slight improvement along the
coast, with mix of MVFR and VFR CIGS.

Farther inland, should remain VFR, with CIGS 4000 to 5500 ft. Lowest
CIGS expected to from Portland northward, and against the Cascades
later this evening. Showers end overnight, but will see CIGS reform
at 3000 to 4000 ft. Little improvement early Sun am.

PDX APPROACHES...Little change into this evening, with CIGS 3500 to
4500 and few light showers or drizzle at times.Clouds break apart a
bit overnight, but the 3000 to 4000 ft CIGS will reform overnight,
persisting into Sunday am.                             /Rockey

&&

.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. Will maintain
current Small Craft Advisory for late Sun afternoon into Monday am,
where have gusts 20 to 25 kt. Does appear will get some gusts in
similar range closer to shore, but suspect most of these will be
stay just offshore. Will expand Small Craft Advisory to include the
nearshore waters (0-10 nm offshore), for Sunday night. Seems
gradients relax early Monday am, with less winds at that time.
Overall, seas stay in 5 to 8 ft through Monday, with highest seas
well offshore.

Then, a taste of fall. A strong front will push across the waters
Tuesday as it elongates/weakens over the coastal waters. 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 vary some on the timing/strength of this
system, so will see how things shape up as get closer in time to
next Tue.

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory from 5 PM Sunday to 5 AM PDT Monday for
     PZZ252-253.

     Small Craft Advisory from 5 PM Sunday to 11 AM PDT Monday for
     PZZ272-273.
&&

$$

www.weather.gov/portland

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