Heisson, Washington Weather Forecast Discussion

008
FXUS66 KPQR 221046
AFDPQR
Area Forecast Discussion
National Weather Service Portland OR
346 AM PDT Mon Sep 22 2025
.SYNOPSIS...High pressure develops and a thermal trough forms through
most of the week with a warming and drying trend. Big headlines
include: above normal temperatures on Tuesday and Wednesday,
and breezy offshore winds on Tuesday.
&&
.SHORT TERM...Now through Tuesday Night...Satellite imagery
shows the ridge aloft forming which is going to keep conditions
dry and settled over the next few days. The ridge is well
agreed upon and shown within the global ensembles. Today we
will see seasonable temperatures throughout the forecast area.
Before looking at the sensible weather on Tuesday, lets dive
into the synoptic pattern which will drive our weather.
Looking aloft, the ridge that was previously mentioned will
build. This process will be aided by a low pressure system in
the northeast Pacific, one over the Rockies, and then a newly
forming low aloft spinning over California. The combination of
those three features will cause the ridge to amplify and usher
in warmer and drier air. A thermal trough will also form at the
surface due to the influx of warmer air. We are expecting higher
than normal temperatures - similar to what was observed this
time last week. The combination of the synoptic pattern with
the temperature gradient at the surface will increase the
probability for gusty easterly winds inland, and gusty northerly
winds along the coast on Tuesday. Looking at the smaller scale
(mesoscale level), pressure and temperature gradients are going
to be a piece of the puzzle. Unfortunately there remains some
inconsistencies with the models. The pressure gradients often
associated with easterly winds (Troutdale to the Dalles) will
tighten to around -3 mb to -4 mb. These gradients correlate to
wind speeds of 15 to 20 mph with gusts up to 30 mph within the
Columbia River Gorge west of the Upper Hood River Valley.
With this being said, not all models are showing the same
process. For example, the ensemble runs from the GFS model show
significantly less wind than the ensembles of the ECMWF. In
Troutdale, peak sustained wind speeds show equal probabilities
of 2-4 mb winds, and 14-16 mph sustained winds. These speeds are
also consistent with the passes of the Cascades - especially
Willamette and Santiam Pass. For the inland north-south aligned
valleys, winds will be northerly and gusty from Salem southward.
All of this to say that one should not be surprised if they wake
up on Tuesday to breezy winds. -Muessle
.LONG TERM...Wednesday through Sunday...Wednesday will see
minimal change in the forecast as the ridge remains anchored
over the region. Temperatures will be a few degrees cooler on
Wednesday and that is mainly due to the position of the low over
California. Overall though, minimal difference will be felt.
Offshore wind will ease slightly on Wednesday, though the
northerly winds inland will persist.
On Thursday the ridge begins to flatten as the low in the
northeast Pacific begins to rotate. The long wave trough
extending from this low will drop southward and thus start to
shift the ridge a bit to the east. Unfortunately, there has
been little improvement in the consistency of the models on
just what will happen on Friday and through the weekend. Right
now there are two different scenarios. The first is if the
trough wins and it moves over the area bringing precipitation
and much cooler temperatures. Could see nearly a 10-15 degree F
drop on Thursday and Friday if this is the pattern that winds
out. If the trough stays further offshore (scenario #2), then
there will still be cooling, but precipitation chances would be
less and then a faster warming on Saturday and Sunday. Wither
either of these options, there is a high probability of an
overall pattern shift back to near normal conditions for late
September over the weekend. -Muessle
&&
.AVIATION...High pressure over the area will lead to widespread
VFR CIGs and VIS. This morning, the clear skies have increased
diurnal cooling and thus, patchy fog is forming along the coast
and inland Cascade Valleys. The fog is forming and dissipating
quickly so have trended towards the lower VIS scenario for coastal
runways. Inland, the atmosphere is drier so it will take a little
longer for fog to form. Based on the current trend, if it does
form inland, it will be short lived and patchy. The areas most at
risk will be within the Willamette Valley along the I-5 corridor,
especially near KEUG and along the river. There is a slightly
higher probability of IFR or low end MVFR CIGs in this region.
Through the day, conditions will clear back to VFR with northerly
winds. Late in the forecast, winds will begin to shift to the
east. This will mainly impact winds aloft (between 1000-4000 ft
AGL) and the Columbia River Gorge.
KPDX AND APPROACHES...VFR through the period with a 40% chance of
IFR CIGs between 14Z-17Z. Given the lower end confidence these
conditions would be temporary and patchy. Winds will shift to the
north in the afternoon becoming gusty at times but not expected to
be strong enough to warrant LLWS. East winds will begin to
increase after 7Z Tue between 1000-3000 ft AGL. Gusts will reach
as high as 30 kt which would mix down to the surface. LLWS is
possible during this time frame. -Muessle
&&
.MARINE...Surface high pressure has begun to rapidly build over
the Northeastern Pacific bringing generally northerly winds
across the waters. Currently, the northerly wind combined with a
northerly fresh swell has caused seas to build hovering right
around Small Craft Advisory levels. While not necessarily
widespread, buoys are showing seas of 8-10 ft at 13 seconds. Have
continued the Small Craft Advisory, but conditions may improve and
warrant dropping that hazard.
Thermal troughing along the coast will yield a tightening
pressure gradient and high confidence in wind gusts reaching 20-25
kt from Tuesday through Wednesday; conditions hazardous to small
craft are very likely. Seas of 6-9 ft at 10-12 seconds will build
to 7-9 ft midweek as winds increase, before easing into the
weekend as high pressure and associated winds weaken.
-Muessle/Picard
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 8 PM PDT this evening for PZZ210-
     251>253-271>273.
&&
$$
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NWS PQR Office Area Forecast Discussion