387
FXUS66 KPQR 232148
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
248 PM PDT Thu May 23 2024

.SYNOPSIS...Weak ridging gives way to yet another trough of low
pressure shifts inland on Friday. Rain returns on Friday through
Saturday but will be showery. non-impactful weather through the
weekend. High pressure builds on Monday through Tuesday which
will cause temperatures to rise.

&&

.SHORT TERM...Now through Sunday...Shortwave trough will slowly
eat away at the weak ridge that is currently stationed over the
Pacific Northwest. This incoming ridge will bring another round
of showers and breezier conditions. Starting synoptically, the
pattern is fairly nondescript as the jet stream is more zonal
until Saturday morning. Shifting to the mid-levels, there is a
bit more energy with a vorticity maximum and shortwave trough
which digs further south over the northern California border.
With this support, will see orographic lift over the Coast Range
and Cascades and thus, enhancing precipitation there. Snow
levels may briefly lower to around 4000 feet Friday night into
Saturday morning, allowing for a dusting of snow as low as the
Cascade passes. Conditions will begin to improve by later
Saturday as the trough departs to the east and makes way for the
next period of shortwave ridging. -Muessle/CB


.LONG TERM...Sunday night through Thursday...A bit more
variability in the long term forecast as we encounter a pattern
shift. Sunday night will transition from zonal flow to general
ridging. On Monday expect clearer skies and warmer temperatures.
As it stands, there is fairly good agreement that we will see
temperatures in the mid to upper 70s through the Willamette
Valley and seasonable along the coast. Ensemble models are all
in good agreement of this ridging pattern with the axis sitting
right over Idaho and Nevada. We will be on the divergent side of
the ridge so there will not be strong winds necessarily, but
with thermally induced low pressure along the coast we cannot
rule out an easterly wind reversal. High pressure intensifies
Tuesday as the ridge shifts eastward.Most of the models are
showing a developing area of low pressure over the Alaska
Panhandle which will slowly shift southward. The ECMWF is the
outlier with this pattern though and keeps that low well to the
northwest. As it stands, light precipitation is possible along
the northern portions of the forecast area. If the ECMWF does
manifest then dry conditions will persist.

By Wednesday the pattern becomes much more convoluted with
widespread disagreement in the overall pattern. Aloft there is
a mix of zonal and much stronger ridging. The most recent
ensembles (as of 12Z) are showing more models with a
strengthening digging trough on Wednesday, while others maintain
a more northerly track. Ultimately it will come down to the
strength of the ridge to determine just how long the spring time
temperatures and clear skies will persist. -Muessle



&&

.AVIATION...Generally VFR with CIGs around 3500-6000 ft. High
pressure will continue to develop over the air space and result in
CIGs lifting to above 7000 ft through at least 00Z Friday. Winds
remain west/northwest at less than 10 kt. Next system will bring a
return of clouds and light precipitation to the airspace. Look
for precipitation to start along the coast around 09Z Friday and
spreading southward through 12Z Friday with a 60-70% probability
of MVFR conditions starting around the same time. Precipitation
will continue spreading inland and reach inland locations
starting around 12Z Friday and also spreading southward through
17Z Friday with a 55-70% probability of a mixture of low end-
VFR/high-end MVFR conditions starting around the same time.

PDX AND APPROACHES...VFR with CIGs around 4000-5000 ft which will
continue to slowly break up and lift over the next few hours.
Winds remain fairly light. Clouds and precipitation will return
starting around 15Z Friday with a 60-70% probability of low end-
VFR/high-end MVFR conditions starting around the same time. -42

&&

.MARINE...Shortwave ridge of high pressure will build over the
area resulting in seas and winds remaining relatively calm through
at least Friday morning. However, a slightly more active pattern
is expected as the next system drops down from the northeastern
Pacific. This system will bring relatively stronger NW winds with
gusts up to 20 kt and seas will also build in response towards 7
to 9 ft with a dominant period of 8 to 10 seconds. The Friday/Saturday
system could bring periods of steep and choppy seas along with
isolated gusts up to 25 kt. However, there is still a fair amount
of uncertainty in the timing and magnitude. Therefore will be
holding off on issuing any Small Craft Advisories at this time.
These elevated conditions will persist through Saturday, with
another weak ridge of high pressure that will bring benign
conditions. -42


&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...None.
&&

$$

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