383
FXUS66 KPQR 082330
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
430 PM PDT Tue Sep 8 2026

Updated aviation discussion.

&&

.SYNOPSIS...Drier and warmer conditions persist through
Thursday with temperatures gradually warming and peaking
Wednesday with the development of low-level offshore flow.
Cooler temperatures return on Friday through the weekend, along
with increasing chances for rain. Forecast uncertainty then
increases by the start of next week.

&&

.DISCUSSION...Now through Monday...Satellite imagery early this
afternoon shows mostly clear skies across NW OR and SW WA.
Ensemble guidance remains in good agreement that upper heights
over the PacNW will raise into Wednesday as the upper low from
previous days continues moving eastward into the Northern Plains
and high pressure over the desert SW slowly spreads into the
Western US. In addition to these two synoptic features over
CONUS, a tropical/sub-tropical low off the coast of California
along with an upper level high over the NE Pacific will create a
col over the Pac NW. This col will help to maintain rather
benign conditions through the middle of the week. At the
surface, a thermal trough will push north from CA, bringing weak
offshore flow (east winds over terrain and the coast and north
winds for the interior lowlands). This overall setup will bring
continued dry weather as well as a brief warming trend into
Wednesday. Daytime temperatures are expected to rise into the
upper 70s to around 80 degrees for the interior lowlands today
and low to mid 80s on Wednesday. Coastal communities will also
be warmer due to the offshore flow, in the upper 60s to low 70s
today and low to mid 70s on Wednesday. There`s around a 5-10%
chance that coastal cities off the immediate coast could reach
80 degrees on Wednesday if offshore flow continues into
Wednesday afternoon/early evening.

Ensemble members remain in good to excellent agreement on the
weather pattern for Thursday into Saturday. On Thursday, a weak
trough begins pushing south into the PacNW, lowering heights
and pushing the surface thermal trough south. This will allow
temperatures to lower back to near to slightly below normal for
early September (upper 70s for the interior lowlands), though
dry conditions will continue.

On Friday, ensemble members indicate another, more robust low
will develop over far western Canadian and drop south into the
PacNW for the end of the week and the start of the weekend.
Uncertainty still exists on the exact track, strength and
timing of this low with 80% of members suggesting the trough
will deepen along the coast while the other 20% suggest the
trough will deepen a little more inland over eastern WA and
eastern OR. As Sunday approaches, the majority of ensemble
models, around 60-70%, indicate the trough will move east of
the Cascades by Sunday morning where the other 30-40% suggest
the trough will linger longer into the day on Sunday with around
10-15% keeping the trough over the PacNW into Monday.

Even with the uncertainty, nearly all members indicate rain
will return to the area sometime between Friday night and
Sunday, though the exact track will determine how much rain and
where it will fall. Friday night into Saturday has the highest
confidence with the latest NBM deterministic forecast now
indicating a 40-50% chance of rain late Friday into Saturday
night across the entire forecast area. Part of the reason for
the lower probabilities is likely more to do with the timing of
when the trough will push through the area as opposed to whether
it will actually rain or not. There`s a 70-80% chance that any
location, within our CWA, will receive at least 0.01 inch of
rain in the 48 hours ending at 5 AM Monday. When looking at
probabilities of reaching or exceeding 0.25 inch in the same 48
hour period, there`s a 30-50% chance for locations west of the
Cascades with a 45-65% chance over the Cascades, including the
foothills. Temperatures will also fall fairly dramatically.
Daytime temperatures will be anywhere from 6-10 degrees cooler
on Friday than Thursday with another 2-6 degrees of cooling on
Saturday. However, the forecast temperature spread increases
Saturday into Sunday as the uncertainty in the weather pattern
increases. The 10th to 90th percentile spread for the interior
lowlands on Saturday is from the low 60s to mid 70s increasing
to the mid 60s to low 80s on Sunday. If you have outdoor plans
this weekend, keep an eye on the forecast and plan accordingly
for the rain potential. Even with the 10-15% of ensemble
members keeping the upper trough over the region on Monday,
members indicate it would weaken and limit precipitation
chances. The rest of the members indicate dry and warmer
conditions for Monday, which is reflected in the deterministic
NBM with precipitation chances less than 10% with temperatures
in the 70s for the interior lowlands. -42/03

&&

.AVIATION...Through 00z Thursday...High pressure over the region
will continue to support widespread VFR conditions across the
airspace beneath largely clear skies. Light offshore flow tonight
will limit chances for low cigs to 10-20% along the coast. If
offshore flow is lighter than expected, cig restrictions will be
more likely. Favored east-southeast winds along Youngs Bay at
KAST may also result in restricted vis within fog/mist overnight
despite the offshore orientation. North to northwest winds build
to 5-10 kt by 18-20z Wed with high confidence in VFR conditions.

KPDX AND APPROACHES...VFR conditions expected through the period.
Diurnal northwest winds ease below 5 kt by 06z Wed, this build to
6-8 kt by 18-20z Wed. High cloud coverage increases late. -36

&&

.MARINE...High pressure offshore will maintain predominately
northerly winds across the coastal waters through the week. A
strengthening pressure gradient today will bring stronger
northerlies with gusts up to 25 kt as there is an 80% chance of
wind gusts exceeding 21 kt by this evening. As a result, Small
Craft Advisories remain in effect from 11 AM Tuesday to 6 AM
Wednesday for the outer coastal waters south of Cape Falcon, and
from 2 PM to 12 PM Tuesday for all other coastal waters. Breezy
north winds continue through Thursday, but should remain 20 kt
or less. Seas of around 4 to 5 ft with a dominant northwest
swell at 10-11 seconds will gradually build to around 6 ft by
this evening as wind chop increases with the northerly winds. A
weak low pressure system is expected to approach the coastal
waters from the north late Friday into Saturday. /DH

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.

WA...None.

PZ...Small Craft Advisory until midnight PDT tonight for PZZ210-
     251>253-271.

     Small Craft Advisory until 6 AM PDT Wednesday for PZZ272-273.

&&

$$

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