373
FXUS66 KPQR 271807
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
1107 AM PDT Fri Sep 27 2024

.UPDATED AVIATION DISCUSSION...

&&

.SYNOPSIS...
Dry conditions and seasonable temps return today in
the wake of a weak cold front. High pressure rebuilds into the
region, bringing gusty northerly winds to the area this
afternoon. Another seasonable day is expected on Saturday before
a weak disturbance passes overhead Saturday night into Sunday.
Below average temperatures are expected on Sunday but no
precipitation. Return to warmer and drier weather early next
week, but uncertainty remains in the forecast from Wednesday
onward.

&&

.SHORT TERM...Now through Sunday...Satellite and radar imagery
depict widespread cloud cover across the area and light rain
showers, mainly north of the Salem. The cold front supporting
these conditions is associated with a low pressure system coming
onshore along the central British Columbia and is located just
off the WA and OR coasts. Light shower activity is expected to
dissipate by 18Z this morning and should only result in light
totals of a few hundredths at any given location.

Expect dry weather today as high pressure re-builds. Surface
high pressure offshore will maintain onshore flow, with winds
shifting more northerly/northwesterly. Winds could get breezy
with gusts up to 30 mph along the coast and 20-25 mph in the
central/southern Willamette Valley. Temperatures will be
seasonable with highs in the low to mid 70s for interior valleys
and 60s along the coast. Friday night, models are indicating a
weak thermal trough developing over the Willamette Valley. This
will lead to light easterly winds over the Cascades, however
winds are not expected to be very gusty/impactful as KTTD-KDLS
pressure gradients are forecast between -2 to -3 mb. Easterly
wind gusts are forecast around 10-15 mph, strongest along the
Cascade crest.

Saturday morning, light easterly winds will continue but the
thermal trough is forecast to break down by late morning. This
will return onshore flow to the Cascades and breezy west winds
through the Columbia River Gorge with gusts to 25-30 mph. Expect
another with seasonable highs similar to Friday.

A weak short wave trough is expected to move overhead Saturday
night into Sunday which will bring slightly below average
temperatures to the area on Sunday. Highs are expected to top
out in the upper 60s inland and upper 50s to low 60s for the
coast. Precipitation is not expected with this wave as the
upper levels remain dry. -Batz

.LONG TERM...Sunday night through Thursday...The majority of
members from the WPC cluster analyses (60%+) depict upper level
ridging returning to the Pacific Northwest early next week. 500
mb heights will be above-average, so this scenario would likely
re-bound temperatures into the low to mid 70s for interior
valleys and mid to upper 60s along the coast. Will note that
models are indicating the potential for a thermal trough
developing again over the Willamette Valley, which would lead to
increased offshore flow over the Cascades Sunday night through
Monday. Forecast relative humidities will fall near critical
thresholds (25%) in the Cascades Mon/Tue, however, recent
rainfall/moisture will help make vegetation less susceptible to
burning.

Confidence wanes into the middle of next week as half of the
members depict continued ridging and the other half begin to
show troughing returning to the area. The NBM temperature spread
between the 25th and 75th percentile also begin to widen by 10
to 15 degrees. We`ll see how the long term forecast shapes up
over the following days. If we maintain ridging then expect
warmer and drier weather, and if we return to troughing then
expect cooler and potentially wetter weather. -Batz/Alviz


&&

.AVIATION...Flight categories remain mixed approaching midday as
cloud cover lingers from weak frontal passage which brought light
rain and mist to the region earlier this morning. Fortunately,
visible satellite is beginning to show this cloud layer dissipate
with improvement back to VFR for all inland sites anticipated
between 19-21z. Beyond this point generally VFR cigs/vis persist
through the evening. It`s worth noting winds this afternoon likely
gust up to 20-27kt along the coast, and up to 10-20 kt inland
between 21Z Friday to 03Z Saturday - lighter winds return
afterward.

PDX APPROACHES...MVFR CIGs likely continue for the next hour or
two before the cloud deck breaks up and dissipates followed by a
quick return to VFR CIGs. NW winds pick up to around 10 kt by
22-23Z with a few gusts around 15 kt possible until 03-05z.
-Schuldt

&&

.MARINE...
Robust low pressure nears British Columbia this morning.
Trailing cold front continues to push through the waters and
onshore, bringing gusty south winds to the waters. South winds
will gust 20 to 30 kt and combined seas at 8 to 12 ft, therefore
will maintain the Small Craft Advisory for all outer and coastal
waters.

High pressure builds over the offshore waters behind the front. As
such, will see a return of northerly winds this afternoon, along
with tightened pressure gradients bringing 20 to 25 kt wind
gusts from Cascade Head southward. These winds will continue
through Saturday. As often is the case, winds will ease a bit
during the overnight and early daytime hours.

The fetch of west to northwest swell from the storm over the Gulf
of Alaska will persist this morning into Saturday, with swell
building to 10 to 13 ft. Along with wind chop, expect overall
seas up 12 to 15 ft, with highest seas farther offshore. While the
swell will decrease tonight, gusty north winds will continued
keep seas somewhat choppy at 6 to 8 ft into Saturday. Winds/seas
decrease Sunday, running at 10 to 15 kt with seas 3 to 6 ft for
early next week. ~Hall/Rockey

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 5 PM PDT this afternoon for PZZ210.
     Small Craft Advisory until 2 PM PDT Saturday for PZZ251>253-
     271>273.
&&

$$

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