Kelso, Washington Weather Forecast Discussion

355
FXUS66 KPQR 070410
AFDPQR
Area Forecast Discussion
National Weather Service Portland OR
910 PM PDT Sat Sep 6 2025
.UPDATE...
Another night where convection has really died down, and the
CAMs (Convective Allowing Models) are not showing anything until
tomorrow afternoon, but I`ve seen that result the last two days
and will admit to being skeptical! We still have a mid level
wave spinning onto land easily seen on Water Vapor imagery,
along the CA/OR border. But the upper level diffluence isn`t
nearly as strong as it was last night, there is no jet moving
through. The HREF ensemble for Comp Reflectivies over 40dbz
shows nothing in our CWA after 05-06z. Radar is showing some
showers moving into the Florence area as I am typing, so it`s
something worth keeping an eye on. 00z KSLE shows that we have
more convective instability than 24 hours ago and this morning.
Updates to the forecast include lowering temperatures from where
we had them and adjusting pops. TEF
&&
.SYNOPSIS...
After another round of showers and thunderstorms
this evening and overnight, expect a considerably cooler and
showery weather pattern through the first half next week.
&&
.SHORT TERM...Now through Tonight...Water vapor satellite
imagery reveals a large upper level low pressure over the
eastern Pacific. An embedded negatively tilted shortwave trough
currently centered over northern Oregon at the moment is
swinging northward into Washington. This feature helped kick off
last night`s thunderstorms that have since moved northward into
the Puget Sound.
In the immediate short term, doppler radar and visible satellite
imagery show thunderstorms developing in a region of 500-1000
J/kg of MUCAPE across far eastern Lane County. These storms
should remain near the crest with areas across the Cascade
foothills and southern Willamette Valley remaining capped this
afternoon due to the ongoing marine clouds and cooler surface
temperatures. High resolution models do suggest the cap will
erode farther north along the Cascade crest so some of these
storms appear likely to ride northward towards Mt Jefferson and
Mt Hood late this afternoon.
Another embedded shortwave trough is currently approaching the
northern California coast and is forecast to slide northward
across western Oregon and western Washington overnight. Large
scale lift ahead of this feature and elevated instability seem
likely to produce another round of convection based on the
pattern across western Oregon and Washington despite most
convective allowing models once again suggesting little to no
activity overnight. Suspect additional updates to the forecast
will be needed this evening as timing and placement of
convection becomes more certain.
.LONG TERM...Sunday through Friday night...Increasing
southwesterly to westerly flow should further scrub the region of
any lingering smoke except in the immediate vicinity of ongoing
wildfires. In general, most of the region will remain dry on
Sunday except for some areas of drizzle along the coast and a
few showers that bubble up over the Cascades before quickly
spreading east of the Cascades in the afternoon hours.
A cool, wet and showery Fall-like weather pattern develops
Monday and continues through at least Tuesday in response to a
closed upper level low that will settle over the region. This
low will bring widespread slow moving showers to the region. As
a result, precipitation amounts will be more patchy and random
in nature than many of frontal rain events. Nonetheless, the
NBM continues to show decent probabilities for at least
0.25-0.50" of rain over much of northwest OR and southwest WA
from the coast to the Cascades between 5 AM Monday and 5 AM
Wednesday. The NBM probabilities for the 0.25-0.50" of rain currently
range from 30-90% for that time period across the region. The
lowest probabilities are generally across the northwestern
portions of our CWA including much of southwest Washington, the
northern Willamette Valley and the north Oregon Coast Range. The
highest probabilities for the higher rainfall amounts is
currently found across the Lane and Linn County Cascades, which
should help slow wildfire activity. With the cloudy/showery
conditions in place, high temperatures will end up well below
average.
The forecast becomes more uncertain midweek onward. This
initially revolves around how quickly the aforementioned upper
low departs the region so showers could easily linger into
Wednesday across the area. Late in the week, 30-40% of the
ensemble guidance brings in another Fall-like trough into the
Pacific Northwest, which would maintain cool temperatures and
bring another good shot of rain to the region. The remaining
guidance suggests temperatures returning closer to seasonal
averages while keeping the area largely dry.
&&
.AVIATION...MVFR ceilings along the coast are expected to
deteriorate to IFR/LIFR conditions by 04-06z Sun, though
conditions could bounce between all three categories through the
night. VFR conditions inland. Onshore flow expected to push
marine stratus into the Willamette Valley once again with a 40-70%
chance of MVFR conditions returning after 09-14z Sun. Expect
conditions to improve to VFR at all terminals by 18-21z Sun.
The chance for isolated showers and thunderstorms continues over
the Cascades through the TAF period. There is also a small
potential for these forming west of the Cascades after 06-09z Sun,
though confidence is extremely uncertain for whether this will
occur. Any thunderstorm activity that may develop will be moving
in from the south- southeast and could include frequent lightning
and small hail.
PDX AND APPROACHES...Low-end VFR conditions around FL035-FL045
continue tonight before deteriorating to MVFR again by 10-13z
Sun. There is a small potential for isolated showers and
thunderstorms after 09z Sun, but confidence remains low. Any
thunderstorm activity that may develop will be moving in from the
south- southeast. -HEC
&&
.MARINE...
An area of low pressure continues to progress through
the waters this weekend, maintaining southerly winds over the
waters. Expect these southerly winds to persist through Monday
and Tuesday before turning northerly again on Wednesday as the low
pressure moves off to the east and surface high pressure returns
to the waters. Additionally, there is a slight chances (15-20%)
for thunderstorms this evening. Seas will generally hold in the
3-5 ft range into early next week. There is a 30-40% chance of
combined seas climbing above 5 ft during the middle next week with
those probabilities climbing to 60-75% by the end of next week.
~Hall/Schuldt
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...None.
&&
$$
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NWS PQR Office Area Forecast Discussion