FXUS66 KPQR 281746 AAA
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
1046 AM PDT Sat Sep 28 2024

Updated Aviation discussion

.SYNOPSIS...Dry weather prevails through at least the middle of
the next week. 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.
Confidence breaks down for the latter half of the week with
cool, wet conditions possibly returning Thu/Fri.

&&

.SHORT TERM...Now through Sunday...A weak thermal trough
developing across the Willamette Valley, supporting weak
offshore flow across the Cascades. The KTTD-KDLS pressure
gradient is expected to peak between -1 and -2 mb leading to
easterly winds 5-15 mph. Models have the thermal trough breaking
down by late Saturday morning which will allow for onshore flow
to return areawide by the afternoon. Another pleasant fall day
is expected with highs peaking around average in the low to mid
70s inland and 60s along the coast.

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. -Batz


.LONG TERM...Sunday Night through Friday...WPC clusters show
high confidence (+90%) that ridging will build across the
eastern Pacific and toward the West Coast to start next week. By
Tuesday, the ridge will build farther inland into the Great
Basin Region and the Rockies, with the axis closer to the coast.
This will support a warming trend back to average on Monday with
highs in the low 70s inland and 60s along the coast. Tuesday
will see a jump back 5-10 degrees above normal with highs in the
upper 70s inland and upper 60s to low 70s for the coast. Models
indicate another thermal trough developing across the area
Sunday night and persisting into Tuesday which will support
offshore flow across much of northwest Oregon and southwest
Washington. NBM suggests a 10-20% chance of wind gusts meeting
or exceeding 25 mph for most areas. The highest chances of
40-60% are along the Columbia River Gorge, exposed peaks/ridges
near the Gorge, and the Cascade crest. Offshore flow will also lead
to daytime RH falling near 25% for portions of the high
Cascades Monday and Tuesday along with poor RH recoveries Monday
night.

By Tuesday afternoon, models suggest that the thermal trough
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. -Batz/Alviz

&&

.AVIATION...Dry southwest flow aloft ahead of an upper level
trough that will push some high clouds across the region today.
Widespread VFR conditions expected across the area. IFR CIGs at
KONP expected to lift with conditions likely improving by 19-20z
this afternoon, though there is around a 20-40% chance of IFR to
lower MVFR conditions persisting through 02z Sunday. Onshore flow
in the lower levels will maintain northwest winds up to 10 kt.

PDX APPROACHES...VFR expected through the TAF period, with
increasing high clouds this afternoon. Northwest winds increase
to around 8 kt later this afternoon. /DH

&&

.MARINE...NW swell continues to subside, decreasing current seas
of 13-15 ft to below 10 ft by this evening. North winds will
continue small craft conditions into Saturday afternoon along the
coast and Saturday night for the outer waters. Another NW swell
will build Tuesday night and Wednesday with combined seas of 12 to
15 ft with wave periods around 16 seconds. Seas are expected to
remain above 10 ft Wednesday and early Thursday. A cold front
will move across the waters late next week.
~Hall/TJ

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory until 2 PM PDT this afternoon for
     PZZ251>253-273.

     Small Craft Advisory until 8 PM PDT this evening for PZZ271-272.
&&

$$

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