FXUS66 KPQR 280441 AAB
AFDPQR

Area Forecast Discussion...Updated
National Weather Service Portland OR
940 PM PDT Fri Sep 27 2024

Updated Aviation and Marine Discussion

.SYNOPSIS...Dry weather prevails through at least through the
middle of the next week. Breezy north/northwest winds this
afternoon will weaken late this evening. Light offshore flow
forecast for the Cascades tonight. Cooler temperatures on Sunday
with a weak disturbance, but not expecting any precipitation.
High pressure builds early next week, leading a warm-up Monday
and Tuesday. Benign weather likely continues mid-week onward.

&&

.SHORT TERM...Now through Sunday...Satellite imagery as of
early Friday afternoon depicts cloud cover beginning to scatter
out. Expect mostly clear skies by late afternoon/evening. We'll
have dry weather as high pressure re-builds over the area, with
highs on track to reach the low to mid 70s for interior valleys
and 60s along the coast. In addition, northerly/northwesterly
winds will strengthen as onshore pressure gradients tighten.
Winds could gust to 25-30 mph along the coast, and 20-25 mph
within the Willamette Valley and I-5 corridor of southwest WA.
Winds are forecast to gradually weaken late this evening as
pressure gradients ease.

Tonight, 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 -1 to -2.5 mb. The strongest easterly wind gusts are
forecast around 15-20 mph, mainly through the central Columbia
River Gorge and over the Cascade crest. Because of this offshore
flow, the high Cascades may experience moderate relative humidity
recoveries.

Light easterly winds over the Cascades are forecast to continue
through tomorrow (Saturday) morning, but the thermal trough is
forecast to break down by late morning. With that, expect a return
to onshore flow by the afternoon. Expect another pleasant fall
day, with high temps forecast similar to today.

Saturday night into Sunday, a weak shortwave trough will move
overhead, cooling temperatures slightly below normal. Sunday
afternoon highs forecast in the upper 60s for interior valleys
and upper 50s to low 60s along the coast. Precipitation is not
expected with this shortwave trough as our air mass will be
relatively dry and the best moisture will be well to our north
over British Columbia.-Alviz

&&

.LONG TERM...Sunday night through Thursday...Medium range
guidance suggests upper level ridging will build over the
Pacific Northwest early next week. This will lead to a gradual
warm-up, with high temps re-bounding into the low to mid 70s on
Monday and upper 70s by Tuesday for interior valleys. Models
also indicate thermal troughs developing along the coast and
Willamette Valley Sunday night and lasting through early Tuesday
morning. These thermal troughs will induce light offshore flow
across much of northwest Oregon and southwest Washington. At
this point, not expecting easterly winds to be too gusty or
impactful. During this time, NBM suggests only a 10-20% chance
of wind gusts meeting or exceeding 25 mph for most areas. The
highest chances of 20-40% are along the Columbia River Gorge,
exposed peaks/ridges near the Gorge, and the Cascade crest.
Offshore flow will lead to daytime humidities falling near 25%
for portions of the high Cascades with poor overnight recoveries
Monday night.

By Tuesday afternoon, models suggest that the thermal troughs
will break down and onshore flow will return. Dry weather will
prevail as high pressure lingers overhead. Wednesday to Thursday,
the majority of ensemble members from WPC cluster analyses show
a ridging/zonal flow pattern with above average 500 mb heights.
In this case, we would continue to experience warm and dry fall
weather. Will note 25% of ensemble members show weak, offshore
troughing approaching the Pacific Northwest on Thursday, which
could bring cooler temperatures and a slight chance for
rain showers. -Alviz

&&

.AVIATION...Inland areas can expect VFR conditions for the next 24
hours with light and diurnally driven winds. Observations at 9 PM
show low ceilings developing at Tillamook, and IFR ceilings at
Florence tonight. North to northeast winds across SW Washington
and NW Oregon should prevent or at least delay low ceilings along
the north coast. Northwest winds will increase Saturday afternoon
across the area with gusts up to 20 kt along the coast.

PDX APPROACHES...VFR for the next 24 hours with light northwest
winds. -TJ

&&

.MARINE...The NW swell that resulted in 15-20 ft seas across the
waters early Friday evening is subsiding and have left the
Hazardous Seas Warning expire at 9 PM. The seas are still
hovering around 15 ft at buoy 46050 (offshore of Newport), but
expect seas to lower to below 15 feet within the next hour or two.
North winds will continue small craft conditions into Saturday
afternoon. Another NW swell will build Tuesday night and Wednesday
with combined seas of 12 to 15 ft with wave periods around 16
seconds. A cold front will move across the waters late next week.
-TJ

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory until 5 AM PDT Saturday for PZZ210.

     Small Craft Advisory until 2 PM PDT Saturday for PZZ251>253-
     271>273.
&&

$$

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