Molalla, Oregon Weather Forecast Discussion

903
FXUS66 KPQR 251749 AAA
AFDPQR
Area Forecast Discussion
National Weather Service Portland OR
1049 AM PDT Thu Sep 25 2025
Updated Aviation discussion
.SYNOPSIS...Cooler temperatures are expected today as onshore
flow strengthens. Another warming trend is expected over the
weekend ahead of an approaching series of frontal system, which
looks increasingly likely to bring rain to the region Sunday
night into Monday. Conditions remain cool and showery
thereafter.
&&
.SHORT TERM...Now through Saturday Night...The pervasive upper
level ridge that has kept conditions unseasonably warm and dry
is beginning to erode and become more zonal. Today will be dry
once again, but cooler with onshore westerly flow. Along the
coast will see breezy northerly winds while northwesterly will
be more dominate inland. In a 180 degree shift, the Columbia
River Gorge will see increased westerly winds - though that will
mainly impact the Upper Hood River Valley. Temperatures today
will lower to near seasonable highs due to the cooler air moving
in.
Late tonight into Friday the initial stages of a shortwave
trough and associated front will move over the region. The front
appears to be staying to the north based on the upper air
pattern so impacts should be minimal. The cool air moving in
will cause overnight temperatures Friday morning to drop by
around 10 degrees within the northern valleys and the Cascades.
Despite the chilly morning temperatures, highs will once again
rebound to seasonable highs in the mid 70s, and 60s at the
coast. Temperatures will warm even more on Saturday, which will
most likely be the warmest day for the foreseeable future with
highs in the mid 70s to lower 80s. That said, there is a 10-25%
chance highs only wind up in the low to mid 70s if excess cloud
cover develops. This increased cloud cover would be due to the
incoming frontal system. If the front shifts further south than
it`s current track, then we could see more cloud cover, and
even some precipitation along the south Washington coast. This
is a very unlikely scenario though as most ensembles show rain
arriving on Sunday. -Muessle/TK
.LONG TERM...Sunday through Wednesday...The long term forecast
is highlighted by a transition to a cool and showery fall-like
weather pattern as a low pressure system in the northeast
Pacific shifts southward. The exact timing for precipitation in
the area is uncertain, as some model guidance suggests rain will
begin as early as Saturday night along the south Washington
Coast, while inland areas are most likely (80% chance) to see it
starting Sunday afternoon/evening. The challenge we will see
with the earlier initiation time (Saturday night or early Sunday
morning) is the amount of dry air present, and whether it would
cause precipitation to evaporate before reaching the ground.
Therefore, higher confidence in more widespread rain on Sunday
evening. Temperatures too will fluctuate based on when and
where precipitation is.
Stratiform rain will continue to intensify on Monday, but
accumulation continues to be a struggle. One example is in
Tillamook on Monday. The 24 hour rainfall totals ending at 11 AM
stretch from 0.15-0.90 inch (10th-90th percentile), with the
mean around a half inch. This trend is mirrored inland where
there is nearly a 0.75 inch difference between the 10th and 90th
percentile in Eugene.
By Tuesday, the low pressure system in the northeast Pacific will
have dropped further south. Ensemble modeled low centers are
showing a chaotic spread of possibilities which encompass almost
all of the offshore waters from Vancouver Island to northern
California. This spread further supports the uncertainty in the
long term forecast. Therefore, will not put too much weight
into the deterministic values on Tuesday and Wednesday, but
there is a high probability that rain and cooler temperatures
will persist into the middle of the week. -Muessle/TK
&&
.AVIATION...Southwest flow aloft turns northwesterly this evening
as a weak upper trough moves over the region. This will bring high
clouds across the area today, with prevailing VFR conditions
through tonight. Onshore flow will continue with north to
northwest winds, generally 10 kt or less through the Willamette
Valley, and breezy at the coast with gusts up to 20 kt.
High pressure builds back over the region later tonight, with
marine stratus likely pushing onshore across the northern coast by
10z Friday. There is around a 50% chance that CIGs fall to MVFR at
KAST. There is also around a 30-40% chance that MVFR stratus
pushing up the lower Columbia reaches the Portland metro between
12-18z Friday morning.
KPDX AND APPROACHES...High confidence of VFR through at least 12z
Friday. Scattered to broken high clouds are expected to pass over
the area today. Then, around a 30% chance of MVFR stratus at the
terminal between 12-18z Friday. Northwest winds expected 10 kt or
less through this evening. /DH
&&
.MARINE...High pressure offshore will maintain northerly winds across
the coastal waters through this evening. Winds have begun to ease
over the waters with speeds around 5-10 kt with gusts up to 15-20
kt. In the afternoon, there continues to be around a 50-60% chance
of gusts greater than 20 kt from Lincoln City southward. However,
these speeds will greatly depend on where the pressure gradient
sets up. In general, the axis is not positioned in a favorable
tilt for very strong north winds and they likely will be isolated.
Have decided against issuing a Small Craft Advisory for this
reason, though there may be periods of gusts up to 25 kt between
1100 AM to 5 PM close to the shore. Seas will ease to 4-6 ft at 10
seconds this afternoon.
Winds ease by Friday as surface high pressure is pushed south by
a frontal system that is expected to stay to the north. Will see
an addition of a stronger northwesterly swell on Friday
afternoon. This fresh swell will build seas back up to around 7
to 9 ft at 14-15 seconds. Model guidance suggests the front stalls
to the north on Saturday, before reinvigorating, approaching the
coastal waters on Sunday. During the timeframe in which it stalls,
wind waves will increase bringing combined wave heights to near 10
ft at 14 seconds. -Muessle/Hartsock
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...None.
&&
$$
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NWS PQR Office Area Forecast Discussion