897
FXUS66 KPQR 050407 AAB
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
849 PM PDT Tue Jun 4 2024

Updated Aviation Discussion

.SYNOPSIS...Showers and gusty winds will diminish across the
area this evening as a frontal system dissipates and high
pressure begins to build in from the south. This will bring
increasing temperatures through the end of the week, with
temperatures peaking around 90 degrees on Friday. Above normal
temperatures then persist into early next week.

&&

.SHORT TERM...Now through Thursday Night...Radar and
observations from around the area show numerous to scattered
showers and gusty south-southwest winds ongoing as a front
pushes across northwest Oregon and southwest Washington this
afternoon, with deep onshore flow in place over the region
anchored by an unseasonably strong upper level jet focused on
Vancouver Island. Despite the blustery conditions by early June
standards, a pattern change will soon commence and bring more
summerlike weather going forward as high pressure starts to
build northward from California, causing the upper level jet to
buckle and shift farther north into Canada. Will see winds
diminish and showers begin to taper off across the area this
evening as the front dissipates, with a few showers lingering in
the Cascades through early Wednesday morning.

Wednesday will bring much more pleasant conditions as the ridge
begins to take shape east of the Cascades, with increasing
subsidence ushering in plenty of sunshine and sending high
temperatures near or slightly above seasonal norms in the low
70s in the interior valleys including the Portland metro.
Temperatures will continue their upward trajectory on Thursday
as models show good agreement on 850 mb temps around 13-15 C,
corresponding to highs in the low 80s. Light north-northeast low
level flow in response to a strengthening thermal trough may
even allow some coastal communities to reach the low 70s by
Thursday. /CB

.LONG TERM...Friday through Tuesday...Temperatures still look to
peak on Friday as the ridge continues to strengthen east of the
Cascades, with the latest guidance holding steady with maximum
temps in the upper 80s to low 90s across the interior lowlands.
This is reflected by NBM probabilistic guidance ranging from
around a 60 percent chance to reach 90 degrees in the
Portland/Vancouver metro to only around a 10 percent chance in
Eugene. The larger change is for Saturday as models have
continues to push the ridge a little farther east and open the
door to stronger onshore flow earlier than had previously been
depicted. As a result, high temperatures for Saturday have
continued to trend towards the lower end of the guidance
envelope, with the NBM now showing only a 15 percent chance to
reach 90 in the Portland metro and less than 5 percent in most
other locations. That said, temperatures will still be solidly
above seasonal norms on Saturday as highs climb into the 80s
again. The other forecast concern for Friday and Saturday as
will be the potential for a few thunderstorms along the Oregon
Cascades as southwest flow aloft allows a few embedded
disturbances and potential some enhanced mid level moisture to
clip the area. The good news is that south-southwest steering
flow would tend to keep any activity that does develop confined
to the immediate crest or points east.

Models diverge somewhat on how the ridge evolves beyond
Saturday as a trough approaches from the Pacific, with some
solutions directing this energy north into Canada while others
try to develop a split flow pattern and shunt some energy south
towards CA as a cutoff low. In terms of sensible weather
impacts, expect mostly dry conditions to persist across
northwest Oregon and southwest Washington with temperatures on
Sunday dropping a few degrees into the upper 70s or low 80s but
generally remaining above seasonal norms. WPC ensemble clusters
show general agreement on maintaining high pressure over the
Pacific Northwest through early next week, while differing on
precise magnitude and placement. Temperatures are therefore
expected to remain above normal through the period, but with a
wider range of outcomes. This is reflected by NBM probabilistic
guidance which shows a 20-25 percent chance to reach 90 degrees
and around a 10 percent chance to reach 95 degrees throughout
the Willamette Valley next Tuesday. However, the 25th percentile
solution would result in temperatures inly in the mid 70s on
Tuesday. Generally speaking, the pattern favors a continuation
of warm and dry weather through the extended, but with less
confidence on where high temperatures will ultimately land. /CB

&&

.AVIATION...Currently a mixture of VFR and MVFR conditions across
most of the airspace. These conditions are expected to slowly trend
towards VFR through the overnight hours and those VFR conditions are
expected to persist into tomorrow as high pressure slowly develops
over the region. However, the weak front which brought light showers
across the region, will continue to push eastward overnight. This is
resulting in the current VFR/MVFR mixture, but guidance is showing
that those MVFR CIGS within the Willamette Valley will propagate
southward and result in MVFR conditions for areas south of KUAO
starting around 08Z Wednesday. These lowered flight conditions are
expected to improve towards VFR around 15Z Wednesday. For coastal
areas expect VFR conditions north of KTMK and the current IFR/LIFR
conditions south of and including KONP will likely linger through
around 17Z Wednesday. Afterwards, expect slow improvement towards
VFR.

North/northwest winds will slacken and slowly become more
northerly through 18Z Wednesday. Expect northerly winds along the
coast to increase around 20Z Wednesday with gusts up to 25 kt.

PDX AND APPROACHES...VFR/MVFR mixture will become predominately VFR
through 08Z Wednesday and continue to improve through 11Z Wednesday.
Northwesterly winds becoming more northerly through the overnight
hours. /42

&&

.MARINE...A frontal system will continue to slowly push onshore
today, sliding south along the coast. Southwest winds around
15-25 kt continue across much of the coastal waters this
afternoon, then are expected to gradually turn northwest and
ease further overnight. Will maintain the Small Craft Advisory as
seas are expected to remain elevated through Wednesday night.

Seas remain steep and choppy at around 10 to 12 feet through
tonight. An incoming northwesterly swell will likely cause seas
to build to around 12 to 14 feet late tonight through Wednesday.

High pressure builds midweek for more settled conditions. Expect
a summertime pattern with high pressure offshore and a thermal
trough along the coast, bringing northerly winds gusting to 25 kt
at times through the end of the week. Seas around 8 to 10 ft on
Thursday likely to subside to around 6 ft on Friday. /DH

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory until 5 AM PDT Thursday for PZZ210-251>253-
     271>273.
&&

$$

www.weather.gov/portland

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