Heisson, Washington Weather Forecast Discussion

657
FXUS66 KPQR 231031
AFDPQR
Area Forecast Discussion
National Weather Service Portland OR
331 AM PDT Tue Sep 23 2025
.SYNOPSIS...High pressure will bring warm and dry conditions
through mid-week. A thermal trough developing tonight will
bring increased offshore flow, especially over the Cascades and
Columbia River Gorge. Cooler temperatures return Thursday with
increased onshore flow. Warming again over the weekend.
&&
.SHORT TERM...Now through Wednesday night...Warm, dry, and
sunny conditions prevail across northwest Oregon and southwest
Washington as an upper level ridge sets up over the Pacific
Northwest. Upper level troughs over the Gulf of Alaska, Southern
California, and the Rockies is amplifying the ridge over our
area and bringing the warm and dry air. Based on the set-up of
the thermal trough, we are seeing these easterly winds
downsloping off the Cascades and Coast Range. Wind speeds are
dependent on pressure gradients, and right now models are honing
in on a -3 to -5 mb forecast gradient across the Cascades and
Columbia River Gorge. This gradient is creating easterly gap
winds through the Columbia River Gorge with gusts to 25-35 mph,
strongest over surrounding ridgetops such as Three Corner Rock
or Crown Point. Pressure gradients ease this afternoon, so winds
will also gradually weaken throughout the day with gusts
falling below 15 mph by the afternoon.
Tuesday to Wednesday will be the warmest and driest days of the
week as the upper level ridge continues to amplify, leading to
above-normal temperatures and relative humidities around 30% or
lower for most places east of the Coast Range. Afternoon highs
each day are forecast in the mid 80s across interior valleys,
and upper 60s to low 70s along the coast. The thermal trough
does re-develop tonight but the axis tilt of the ridge is not as
favorable for strong offshore winds.
On Thursday, the thermal trough will weaken as the ridge
flattens and becomes less organized. The area sits right in the
middle of diverging flow which will make the weather much more
variable. Still will be warm and dry, but will incorporate some
component of onshore flow. The low over northern California will
shift southward during the day allowing for cooler and moister
air to begin to push into the area from the northeast Pacific.
-Muessle/Alviz
.LONG TERM...Friday through Monday...Zonal flow aloft persists
on Friday through Saturday which means that conditions overall
will see minimal change. Saturday will be a transition day as a
long wave trough will drop down towards the coast. This means
that temperatures will start to shift on the cooler side. Will
say, that 24-hr maximum temperatures show a fairly wide spread
with nearly a 10-15 degree F difference between the 10th and
90th percentile. For example, along the Coast Range and
Cascades, the low end maximum temperature on Saturday is 69
degrees F, and the high end (90th percentile) is around 80
degrees. Within the Willamette Valley and Upper Hood River
Valley there is less of a difference but still fairly wide with
high end temperatures in the mid-80s.
On Sunday into Monday there is much better agreement in the
ensemble modeled 500 mb heights of lowering heights moving in.
This trend will cause temperatures to decrease and moisture to
filter in. At the surface, there is a cold front moving in which
could bring precipitation. There has been a trend of
precipitation being delayed a day at a time with it now arriving
on Monday. Looking at the global models, there is a 10% chance
of accumulating rain arriving along the coast as early as
Saturday morning, and a 10% chance of it arriving as late as
next Tuesday morning. The mean (more likely scenario), it
arrives late Sunday or Monday morning. This is just one example
that depicts the overall uncertainty in the long term forecast.
-Muessle
&&
.AVIATION...High pressure with widespread VFR conditions. Winds
will be the challenge in the forecast over the next 24 hours due
to a combination of northerly winds from the Willamette Valley
west, and easterly winds through the Columbia River Gorge and the
Cascades. Gusty winds are expected within the Willamette Valley,
but the Columbia River Gorge will experience the strongest
easterly winds. Above 1000 ft MSL wind gusts will reach 30 kt.
Areas within the Gorge will experience speed based LLWS as
surface winds will be slightly lower. In addition, gusty
conditions are expected through the Cascade valleys and on the lee
side of the slopes due to downsloping.
Along the coast, saturation is occurring which will increase
chances for coastal radiational fog this morning. If fog or IFR
stratus does form, it will be short lived and patchy. Overall
easterly flow will ease once again after 06Z Wed which increases
chances for IFR CIGS/VIS along the coast.
KPDX AND APPROACHES...VFR conditions with northerly flow. Easterly
winds will be amplified by the Columbia River Gorge causing LLWS
through the afternoon. LLWS will be generally speed based and
between 1000-2000 ft MSL. Gusts will mix down to the surface
around 18Z Tue.-Muessle
&&
.MARINE...Building surface high pressure over the northeastern
Pacific will continue to support northerly winds of 10-15 kt
across the waters. Seas have eased from the Small Craft Advisory
conditions from yesterday, but still seeing near criteria seas.
Have decided to maintain the advisory for the near term, but will
evaluate through the morning. Through the afternoon, the thermal
trough will intensify causing northerly winds to increase in a
typical summer pattern. Northerly winds will rise with gusts up to
25 kt in the evening. These winds again will be marginal so will
consider another advisory.
Seas will build again to 8-10 ft midweek as winds increase.
Conditions then improve as winds and seas ease into the weekend as
high pressure weakens.-Muessle
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 11 AM PDT this morning for
     PZZ251>253-271>273.
&&
$$
www.weather.gov/portland
Interact with us via social media:
www.facebook.com/NWSPortland
x.com/NWSPortland

NWS PQR Office Area Forecast Discussion