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757
FXUS66 KPQR 080942
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
242 AM PDT Sat Jun 8 2024

.SYNOPSIS...
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High pressure of varying intensity across the
Pacific Northwest will maintain mostly above average temperatures
and dry conditions through at least the middle of next week.
Precipitation chances (15-35%) peak across the Cascades this
evening into early tomorrow morning. Precipitation chances
across northwest Oregon and southwest Washington potentially
return late next week.
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&&

.SHORT TERM...
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Today through Sunday night...The high pressure
ridge aloft will begin to shift eastward today as an upper-
level shortwave trough approaches the Pacific Northwest. Signs
of this weak system are evident on satellite imagery as of 230
AM PDT, where a band of mid to high level clouds are approaching
130W far offshore of the WA/OR coast. Precipitation is unlikely
across most of the CWA today as this shortwave trough will be
entering a very dry air mass. Interior valleys will still
maintain above average temperatures today, but expect to be a
few degrees cooler than yesterday due to increasing cloud cover.
Afternoon highs are forecast in the low 80s for interior
valleys, with 60s along the coast as onshore flow persists. Also
expect some morning marine stratus at the coast which will
likely burn off by mid to late morning.

A slightly more southerly component to SW flow aloft will allow
for increasing chances for showers and thunderstorms across the
Cascades this evening and tonight. Surface heating and upslope
flow may help trigger shower development in the Cascades - HREF
guidance shows MUCAPE values of 250-1000 J/kg along the Cascade
crest. However, the CAMs seem to suggest that most shower and
thunderstorm activity will be east of the Cascades. The westerly
component to flow aloft will help with pushing showers and
thunderstorms eastward. Thus, the low PoPs (15-35%) over the
Cascades and low thunderstorm chances over the Lane County
Cascades (<20%) look reasonable.

Sunday, the weak trough will push inland and exit the region.
Temps will continue to cool slightly, with Sunday afternoon
highs forecast in the upper 70s for inland valleys and 60s along
the coast. NBM guidance suggests only a 20-40% chance that the
Willamette Valley exceeds 80 degrees. By Sunday night, high
pressure will re-build behind the exiting trough which will lead
to decreasing cloud cover.      -Alviz
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&&

.LONG TERM...
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Monday through Friday...WPC cluster analyses are in
agreement of 500mb heights remaining above average through mid-
week (Wed). This will support temperatures remaining above
average across northwest Oregon and southwest Washington until
then. Ensemble guidance are in agreement of ridging over the
Pacific Northwest on Monday, but the ridge begins to flatten
Tuesday-Wednesday as a trough near the Gulf of Alaska pushes
lower 500mb heights into British Columbia. This would result in
a slight cooling trend. Thursday, most ensemble members (75%)
suggest that ridging will persist over the Pacific Northwest.
However, 25% of members suggest that the aforementioned trough
near Alaska will begin to dip southward and bring more
southwest flow over us. By Friday, the majority of ensemble
members have the trough dropping close enough to the Pacific
Northwest to return rain chances to our area. Meanwhile, 20% of
the ensemble members keep the ridging on Friday with drier
conditions.       -Alviz
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&&

.AVIATION...
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VFR conditions over the region as high pressure
lingers. SKC this morning aside from some coastal terminals which
are experiencing upwelling stratus and mist. Will see a 40-50%
chance of MVFR CIGs and VIS from KTMK southward - especially
around KONP. A decaying front is dropping down from the northeast
Pacific this afternoon and will push a VFR stratus shield over
the region after 20Z. Winds will be weakly northwesterly. Towards
the end of the forecast, widespread lower stratus will begin to
advect inland. Around 09Z Sunday the front will make landfall and
begin to fill in the coast with IFR stratus. Coastal terminals
from KTMK northward have a 90% chance to see IFR stratus and 25%
chance of IFR VIS simultaneously. Precipitation will follow. For
areas south of KTMK, the stratus will arrive a few hours later.
There is a lack of confidence as to when this stratus will reach
areas around KKLS, but so far it looks to be after the end of this
TAF package.

PDX AND APPROACHES...Surface high pressure dissipates today. VFR
with typical northwesterly flow over the next 24 hours. A layer of
VFR stratus will begin to fill in around 18Z Saturday but will be
non-impactful. Will mention that around 02Z Sunday northwesterly winds
just off the surface will be higher (around 15-20 kt) vs the
surface which will struggle to exceed 10 kt. -Muessle
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&&

.MARINE...
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The high pressure that has prevailed over the last few
days will slowly weaken through the day today. Will maintain the
northwesterly winds, but speeds will be slower. Winds will
generally be around 10-15 kt with gusts up to 20 kt. This evening
a decaying front will drop down from the northeast Pacific which
will cause a slight shift in the weather. The main impact will be
to winds. There is a slight chance (around 20%) that we could see
gusts up to 25 kt this afternoon in the northern waters, but
ultimately it will come down to the timing of the system and the
strength.

Because the front is already weak and it is trying to
break down a stable high pressure, it could decay even further
than currently expected. The peak of the front will occur very
early Sunday morning. High resolution models are suggesting a
heightened probability (>75%) of marginal small craft advisory
winds. However, given the nature of the system, they may not be
frequent enough to qualify the waters (specifically PZZ251/271)
for an advisory. Will continue to keep an eye on manifesting
conditions today as we cannot rule it out completely. Seas will
rise a few feet from the current conditions of 5-6 ft at 11
seconds. Guidance suggests seas around 8-9 ft at 12 seconds late
Sunday night with the frontal passage - likely due to the
increased wind waves.

Conditions will once again settle on Monday before yet another
weak disturbance moves inland on Wednesday. Will mention that as
of this forecast, the frontal system is tracking further north so
we may just see the residual impacts. -Muessle
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&&

.PQR WATCHES/WARNINGS/ADVISORIES...

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OR...None.
WA...None.
PZ...Small Craft Advisory until 8 AM PDT this morning for PZZ210.
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&&

$$

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