Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 012053

Area Forecast Discussion
National Weather Service Portland OR
152 PM PDT Sat Oct 1 2022

.SYNOPSIS...High pressure over the region will maintain warm and dry
conditions for much of southwest Washington and northwest Oregon for
the first week of October.


.SHORT TERM...Tonight through Tuesday...Models and their ensemble
systems are in good agrement shortwave ridging over the northeast
Pacific will gradually shift eastward across the Pacific Northwest
through Tuesday and result in a continuation of warm and dry weather.
With that said, a modest easterly wind event currently underway
across the region will gradually wane over the next 24-36 hours. A
southerly wind reversal will spread fog and low clouds up the coast
beginning late tonight before it reaches the south Washington coast
Sunday afternoon. Some of this cooler marine air will gradually
filter into the Willamette Valley Monday and Tuesday and result in
inland temperatures cooling a couple degrees each day. Nonethless,
high temperatures still look to top out near 80F in the Willamette
Valley and Columbia River Gorge on Tuesday. This is still near 10F
warmer than average for early October. /Neuman

.LONG TERM...Tuesday night through Saturday...Models and their
ensembles are more or less in agreement the region will remain warm
and dry through the end of the week. Nonetheless, there are some
subtle variations to the large scale pattern that do influence
temperatures and to a lesser degree light rain chances by next Friday
or Saturday. Approximately 15% of ensemble guidance suggests a
shortwave trough will drop down the spine of the Rockies and bring a
backdoor front into the region that would result in cooler
temperatures and some easterly winds by Friday. Another 15% of the
ensemble guidance suggests shortwave ridging will flatten and shift
just far enough east to allow moist southwesterly flow to bring a
chance for light rain to our far northwestern zones by Saturday.
However, NBM4.0 guidance only raises PoPs into the 1-5% range late
Saturday so have maintained a dry forecast for now. /Neuman


.AVIATION...Widespread VFR under clear skies expected to continue
through at least 10Z Sunday. Gusty north/northeast winds across
the Willamette Valley along with east winds near the western mouth
of the Columbia River Gorge through this evening. Gusts to 20-25
kt likely at both KTTD and KPDX and gusts in the 15-20 kt range
for the remainder of the Willamette Valley through at least 00Z
Sunday. The easterly surface winds continue tonight at KTTD, with
overall flow weakening and becoming more northerly/northwesterly
for other locations within the Willamette Valley. Onshore winds
continue along the coast tonight, but a southerly flow reversal
over the waters will bring increasing probabilities for IFR/LIFR
conditions starting around 10Z Sunday. These lower lower flight
conditions will spread northward along the coast through Sunday,
likely reaching KONP around 10Z Sunday, KTMK around 14Z Sunday
and KAST around 20Z Sunday. Inland areas expected to remain VFR
through Sunday.

For detailed Pac NW aviation weather information, go online to:

KPDX AND APPROACHES...VFR flight conditions under clear skies
through the end of the forecast period. Gusty east winds up to 25
kt starting around 20Z Saturday. Winds ease and become more
northerly/northwesterly by this evening. /42


.MARINE...Current observations from buoys 29 and 50 show wind
gusts around 10 to 15 kt, while buoy 89 has gusts near 20 kt.
This suggests the thermal low remains offshore with the strongest
winds beyond 60 NM. The thermal low will likely retreat towards
the coastline causing winds to re-build this afternoon and
bringing Small Craft Advisory gusts back into the forecast for
zones PZZ272 and PZZ273 through tonight. Winds will slacken with
sustained winds less than 10 kt with a southerly wind shift
expected to start Sunday morning and move south to north through
the daytime hours.

The combination of the northwest swell and northerly wind waves
will yield significant wave heights in the 4 to 6 ft range with a
dominant period of around 10 to 12 seconds. Seas will subside
Sunday morning and will result in seas subsiding to 3 to 5 ft at
10 to 12 seconds by mid Sunday morning.

Beginning early Sunday morning, the southerly flow reversal
appears increasingly likely to bring reduced visibilities into all
zones. A Dense Fog Advisory may be needed starting late tonight or
early Sunday morning, but will hold off on issuing one as timing
the southerly reversal is a challenge.

Next week, high pressure looks to stay over the waters, keeping
rather benign conditions. Depending on where the coastal thermal
trough sets up along the shoreline, gusty northerly winds could
redevelop as early as Wednesday. /42

For information about recent marine zone changes, go online to:



PZ...Small Craft Advisory from 5 PM this afternoon to 3 AM PDT
    Sunday for coastal waters from Cape Foulweather OR to Florence
   OR From 10 to 60 nm.



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