Castle Rock, Washington Weather Forecast Discussion

724
FXUS66 KPQR 101830 AAA
AFDPQR
Area Forecast Discussion...UPDATED
National Weather Service Portland OR
1130 AM PDT Wed Sep 10 2025
Updated aviation discussion.
&&
.SYNOPSIS...Mainly dry weather is in store Wednesday through
Saturday with seasonable temperatures. One exception is in the
Oregon Cascades, where showers and thunderstorms are expected
once again Wednesday afternoon and evening. Showers will linger
over the Cascades on Thursday as well. The forecast becomes more
uncertain Sunday onward, however odds slightly favor cooler and
wetter weather Sunday into Monday with a 50-70% chance of rain.
&&
.DISCUSSION...Now through Tuesday night...Satellite and surface
weather observations from early Wednesday morning depicted low clouds
over nearly all of northwest OR and southwest WA along with light and
variable winds. Showers and thunderstorms have dissipated, but are
expected to return to the Oregon Cascades this afternoon, mainly to
the south of Mt. Hood. Similar to the past few days, stronger showers
and storms will produce locally heavy rain with rainfall rates up to
0.5-0.75 in/hr. Locations west of the Cascades will likely stay dry
with mostly cloudy skies, although some breaks in cloud cover are
expected towards 2-5pm. Expect pleasant temperatures with afternoon
highs in the 70s, except 60s in the high Cascades and at the coast.
Chances for showers and thunderstorms will continue for the Cascades
Wednesday night through Thursday as a slow-moving upper level low
pressure system gradually shifts into northern Nevada, eastern Oregon
and Idaho, bringing some wrap-around moisture to the area. Meanwhile,
dry weather and mild temperatures will continue west of the Cascades
with conditions on Thursday very similar today.
By Friday, models and their ensembles remain in good agreement a
shortwave ridge will begin pushing into western WA/OR from the west,
on the backside of the aforementioned low pressure system. This ridge
will bring dry weather across the region with warmer temperatures on
Friday and Saturday. Expect morning cloud cover in the lowlands and
afternoon sun both days, with high temperatures in the upper 70s to
lower 80s for inland valleys, and upper 60s at the coast.
Forecast confidence lowers considerably from Saturday night onward as
models struggle to resolve the evolution of an upper level trough
that will move towards the Pacific Northwest from the northeast
Pacific. Some ensemble guidance suggests this trough will slow down
before making landfall and form a closed cut-off low that dives
southeastward into northern California. This scenario would result in
very little to no rain and warmer temperatures Sunday into early next
week. Other ensemble guidance shows the trough moving into western
WA/OR without forming a cut-off low. This scenario would bring
widespread rain to the area and cooler temperatures Sunday into early
next week. Probabilities slightly favor the cooler and wetter
scenario, and QPF plumes from the ENS/GEFS/GEPS ensembles all show
ensemble member clustering between a few hundredths of an inch and
0.2 inches for QPF amounts, suggesting rain will most likely be
light if it does occur. Admittedly, there are a few outlier members
around 1 inch, but the probability for rain amounts that high are
only at 1-5%, except 10-20% in the Cascades and Coast Range. -TK
&&
.AVIATION...MVFR CIGs are currently in place across the area with
satellite imagery indicating only small pockets of the cloud deck
beginning to dissipate. Expecting CIGs to improve to VFR early
this afternoon for most location, slightly later in the mid
afternoon along the coast. Winds out of the north/northwest at
5-10 kt through the day. Expecting marine stratus to push into the
coast again after 00-03z Thu supporting MVFR/IFR CIGs. Guidance
suggests stratus pushes inland between 10-12z Thu, bringing MVFR
CIGs to much of the Willamette Valley.
Low pressure is far enough south to keep conditions mainly dry
today, however, a 15-30% chance for showers and thunderstorms
remains for the Cascades and Cascade foothills this afternoon
between 21z Wed to 03z Thu. There is less than 10% chance that a
thunderstorm moves westward into the Willamette Valley, but could
see a stray shower or two over KEUG.
KPDX AND APPROACHES...MVFR CIGs as a stratus deck remains in
place late this morning, expecting it to dissipate early this
afternoon. VFR conditions with northerly winds around 5 kt
expected through early tonight. Another marine push is expected to
bring MVFR (possibly IFR) CIGs between 10-12z Thu. -Batz/Alviz
&&
.MARINE...High pressure over the waters will maintain northerly
to northwesterly winds with gusts less than 15 kt through
Thursday. Winds become more variable across the waters on Friday
ahead of the next system, but still remain light. Expect seas
around 3-4 ft at 11-12 sec today, building to 5-6 ft at 13-14
sec Thursday to Friday with a west-northwesterly swell. In
addition, a Small Craft Advisory has been issued for the
Columbia River Bar for a strong ebb between 5-10 PM today
(Wednesday), with seas up to 7 ft.
Heading into the weekend, another low pressure system in the
northeast Pacific will approach the Pacific Northwest. A front
associated with this low will weaken as it moves across the waters
Saturday and Sunday. The winds will shift southerly ahead of the
front on Saturday, then northerly with and behind the front by
Sunday afternoon. Probabilities for observing wind gusts of 21 kt
or greater (small craft conditions) across the waters in a 24 hour
period on Saturday range from 30-50%, highest across the outer
waters. Probabilities increase Sunday to 50-70% for all marine
zones. However, 1-hour probabilities for small craft gusts are
only 10-15%, suggesting that any small craft wind gusts may be
brief and not as frequent/long-lasting. Given the lead time and
some uncertainty with the exact low track, will hold off on
issuing any products for now. Seas are forecast around 6-7 feet
at 10-12 sec through the weekend.        -Alviz/Batz
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory from 5 PM this afternoon to 10 PM PDT
     this evening for PZZ210.
&&
$$
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NWS PQR Office Area Forecast Discussion