519
FXUS66 KPQR 261204
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
504 AM PDT Thu Sep 26 2024

.SYNOPSIS...Quiet, seasonable conditions expected today aside
from lingering fog during the morning. Another weaker front
arrives overnight late today into Friday morning. High pressure
returns over the weekend. A slight warm up back to slightly
above average possible early next week. More active weather
possible mid next week.

&&

.SHORT TERM...Now through Saturday...With the passage of a
cold front yesterday, PNW is now in a post frontal airmass.
Clear skies and calm winds have allowed temperatures to drop
into the upper 40s to low 50s so far and combined with the wet
ground from yesterdays rains have produced patchy areas of fog
across northwest Oregon and southwest Washington. Nighttime
microphysics satellite imagery as of 1030Z along with ASOS
observations show fog expanding throughout the Willamette
Valley, prompting a Dense Fog Advisory until 11 AM. Dense fog is
possible during the morning commute so slow downs are possible.

The system that brought rain to the area yesterday will lift
northeast, leaving quasi-zonal flow across the region for most of
Thursday. Conditions will be dry with seasonable temperatures
in the low to mid 70s inland and mid to upper 60s along the
coast. A weaker cold front associated with a low coming onshore
across central British Columbia will bring a chance for light
rain showers late Thursday. The best chance for rain will be
across southwest Washington and the Coast Range of Oregon with
generally a few hundredths expected and up to a quarter inch
locally. Friday and Saturday are both expected to be around
average temperature-wise. Friday could see some gusty north
winds as high pressure over the northeast Pacific builds towards
the PNW, tightening the pressure gradient across the region.
Gusts around 30 mph will be possible along the coast and 15-20
mph inland. Upper level flow shifts southwest as a large trough
approaches from the west. Models show a weak thermal low
developing across western Oregon late Friday along with weak
offshore flow east of the Willamette Valley, Friday night into
Saturday morning. The pressure gradient between The Dalles and
Troutdale is expected to be around -2 to -3 mb so easterly winds
around 10 to 15 will be possible during that period. -Batz

&&

.LONG TERM...Saturday Night through Wednesday...The surface high
moves eastward over Washington and Oregon while a trough moves
overhead in the upper levels. This will bring below average
temperatures in the upper 60s inland and upper 50s along the
coast for Sunday. A dampened ridge is expected to develop across
the West Coast which will support an upward trend in
temperatures to Start next week. Approximately two thirds of the
WPC clusters support this pattern with the remaining third
supporting ridge development offshore. If the ridge sets up
onshore, temperatures inland will reach the mid to upper 70s for
Monday and Tuesday with mid to upper 60s along the coast.
Confidence wanes into the middle of next week with approximately
one third of the members depicting each of the following
solutions, ridging offshore, ridging centered over the Great
Basin, and the last with the ridge toward the center of the
country and zonal flow across the PNW. Next week is very much up
in the air at this time. Another weak thermal low could develop
Monday through Tuesday which could support weak offshore flow
at times east of the Willamette Valley. -Batz

&&

.AVIATION...Westerly flow aloft with high pressure in place over
the area. Cool and moist conditions at the surface will likely
produce widespread, potentially dense fog this morning. The fog
and/or stratus is expected to dissipate around 16-18z later this
morning, with widespread VFR conditions returning to the area.
Southerly winds are expected to increase along the northern OR
coast this afternoon, with gusts up to 20 kt. A weak front will
push toward the coast later today with chances for MVFR and IFR
stratus increasing (>80%) after 04z Friday.

PDX APPROACHES...VFR as of 10z, but fog is developing quickly at
surrounding terminals and should push into KPDX by 12z. IFR
conditions likely through at least 16z, then fog lifts and
eventually scatters out by 17-19z. VFR expected this afternoon
through at least 06z Friday. A weak front will likely push low
clouds into the area with a 50-70% chance of MVFR CIGs between
09-12z Friday. Generally expect southeast winds up to 5 kt. /DH

&&

.MARINE...A 983 mb low in the far NE Pacific will continue to
strengthen as it moves toward Haida Gwaii today. Southerly winds
will gradually increase as the frontal system associated with
this low approaches the coastal waters. The strongest winds are
expected across the northern zones, peaking this afternoon and
evening with gusts up to 30 kt, except for the northwest corner of
PZZ271 where gusts to 35 kt are likely between 2 PM and 8 PM PDT.
Will maintain a high-end Small Craft Advisory for the coastal
waters generally north of Cape Falcon through this evening. The
trailing cold front is expected to weaken as it moves across the
coastal waters tonight. Seas within the zone of strongest winds
today are also likely to become steep and potentially hazardous,
building to around 8 to 12 ft.

A westerly swell moving in behind the front is expected to
continue to build seas to around 12 to 15 ft tonight through
Friday. High pressure also rebuilds on Friday, along with a
strengthening thermal trough along the southern Oregon coast. This
will result in a return to gusty northerly winds. Gusts up to 30
kt are very likely (80-90% chance) off much of the central Oregon
coast. The westerly swell combined with northerly winds will
likely create a chaotic sea state. A Small Craft Advisory has been
issued for Friday and Friday night, but will need to monitor for
the potential to be upgraded to a Hazardous Seas Warning.

Northerlies are expected to continue through the weekend, while
seas settle to around 8 to 10 ft. Seas likely subside further into
early next week. /DH

&&

.PQR WATCHES/WARNINGS/ADVISORIES..

OR...Dense Fog Advisory until 11 AM PDT this morning for ORZ108>118.

WA...Dense Fog Advisory until 11 AM PDT this morning for WAZ204>207.

PZ...Small Craft Advisory from 5 PM this afternoon to 5 PM PDT
     Friday for PZZ210.

     Small Craft Advisory from 2 PM this afternoon to 5 AM PDT
     Saturday for PZZ251.

     Small Craft Advisory from 5 AM Friday to 5 AM PDT Saturday for
     PZZ252-253-273.

     Small Craft Advisory from 11 AM this morning to 5 AM PDT
     Saturday for PZZ271.

     Small Craft Advisory from 5 PM this afternoon to 5 AM PDT
     Saturday for PZZ272.

&&

$$

www.weather.gov/portland

Interact with us via social media:
www.facebook.com/NWSPortland
x.com/NWSPortland