438
FXUS66 KPQR 292152
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
252 PM PDT Sun Sep 29 2024

.SYNOPSIS...Westerly flow aloft will maintain dry weather with
variable clouds today. High pressure will build inland over Pac NW
tonight into Monday, with light offshore flow with bit warmer
temperatures for Monday and Tuesday. Mild and dry weather continue to
end of the week, but does appear cooler wet weather returns next
weekend.
&&

.SHORT TERM...(Today through Tuesday)...A weak trough continues to
pass through, creating slightly cooler and more moist conditions
throughout today. Temperatures show only a 20-30% chance of exceeding
70 in the Willamette Valley today. This pattern won`t last long, as
ridging begins to build in tonight going into Monday. Temps gradually
warm Monday and Tuesday, with Tuesday seeings temperatures in the
upper 70s for most areas. RH values will also be drier, with daytime
minimum RHs around 20-30%.

Winds will shift more northeasterly beginning late tonight into
Monday morning as the thermal trough redevelops at the coast, with
breezy easterly gusts at times through the Columbia Gorge and
Cascades channels aligned east to west. Gusts at those locations may
get up to 25 mph on Monday afternoon. In the Willamette Valley,
northerly winds may produce gusts up to 20 mph Monday afternoon. On
Tuesday, flow gradually becomes onshore again as the thermal trough
returns east of the Cascades.

High pressure will build into western Washington later today and
tonight, and remain in that position for next few days. At the same
time, will see thermal low pressure along the south Oregon coast that
will strengthen and build north along the Oregon coast. While this
will turn our flow more lightly offshore, with bit warmer conditions
for Monday and again Tuesday. Winds not likely to be all that strong,
with mostly 10-20 mph for more east-wind prone areas such as the
mid/lower slopes of the Cascades, western Columbia Gorge into far
east Portland/Vancouver metro, and over the Coast Range for Monday
into early Tuesday. But, as is often the case during this time of the
year, main effects of such patterns is more noticeable during the
overnight hours. That is for drier conditions overnight, with milder
temperatures and lower humidity in the windy areas. In areas where
winds are light (ie, those sheltered from offshore winds),
temperatures will drop into the upper 30s to middle 40s. But, in
area where wind stays up, overnight temperatures likely to remain in
the 50s.  Ahhh, fall weather, with cool nights and warm afternoons,
or in other words:  great pumpkin patch weather.

.LONG TERM...(Wednesday through Saturday)...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.
Increasing agreement on troughing returning next Thursday night into
Friday morning, with some better potential for cooler and showery
weather for next weekend. Precipitation still looks fairly light, and
temperatures will likely return to around 70. /Batz/Liu

.AVIATION...Upper ridge building offshore with dry northwest flow
over the region. Low level onshore flow from the north Oregon
coast into Washington bringing some cumulus with BASES around
4000-5000 ft, generally north and west of KPDX-KUAO. VFR expected
to prevail inland through 00Z Tue at TAF sites. Coastal areas also
expected to remain VFR but patchy fog or low stratus may develop
overnight.

Winds north to northwest in the inland valleys with gust 10 to 25
kt through this evening, strongest wind toward the KEUG area.

&&

.MARINE...High pressure centered offshore gradually strengthens
as it pushes northeast toward the Washington coast this weekend.
Pressure gradients begin to strengthen tonight with gusts up to
20-25 kt possible for the waters south of Cascade Head through
Monday. Overall, breezy northerly winds this week as the thermal
trough strengthens along the Oregon coast. However pressure
gradients weaken Tuesday as a weak front pushes through the high
pressure. This front associated with a low pressure moving into
the Gulf of Alaska Monday, Tuesday. Also with this system, a
developing northwesterly swell will likely push seas up again over
10-15 ft across the coastal waters beginning late Tuesday and
into Wednesday. /mh

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory from 5 AM to 8 PM PDT Monday for PZZ252.

     Small Craft Advisory until 8 PM PDT Monday for PZZ253.

     Small Craft Advisory from 5 AM Monday to 3 AM PDT Tuesday for
     PZZ272.

     Small Craft Advisory until 3 AM PDT Tuesday for PZZ273.
&&

$$

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