068
FXUS66 KPQR 081808 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
1108 AM PDT Sat Jun 8 2024

Updated aviation and marine discussions.

.SYNOPSIS...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.

&&

.SHORT TERM...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

&&

.LONG TERM...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

&&

.AVIATION...A weak upper level disturbance was moving northward
over northwest OR and southwest WA at 1730Z Saturday, bringing a
band of high clouds with cigs over 20 kft. Virga was being sampled
by the KRTX radar with this band of high clouds, meaning
precipitation
is evaporating before reaching the ground. As such, VFR
conditions will continue across the area Saturday afternoon
through Saturday night. Probabilities are very high (90% or
higher) for the return of a marine stratus deck along the coast
towards sunrise on Sunday, with cigs most likely ranging between
500-1000 ft. While this marine push looks to be weak with limited
inland extent, there is a 15-25% chance the marine stratus deck
will end up extending as far inland as KHIO/KPDX/KTTD (however for
a short period of time between 15-18Z Sunday). Even if the
stratus deck is able to push that far inland, conditions would be
MVFR at worst and would quickly improve back to VFR after 18Z
Sunday. Surface winds will generally be out of the northwest
Saturday afternoon, under 10 kt.

PDX AND APPROACHES...VFR with typical northwesterly flow over the
next 24 hours with periods of broken high clouds (cigs over 20
kft). It still appears northwesterly winds just off the surface
Saturday evening will be higher (around 15-20 kt) when compared
to surface winds which will likely stay under 10 kt. There is
around a 25% chance for a brief period of 2000-3000 foot cigs
between 15-18Z Sunday.-TK

&&

.MARINE...The high pressure system that has prevailed over the
last few days will slowly weaken through the day today as a
decaying upper level front moves through. Will maintain the
northwesterly winds, but speeds will be slower. Winds will
generally be around 10-15 kt with gusts up to 20 kt. There is a
slight chance (around 20%) that we could see gusts up to 25 kt
this afternoon in the northern waters, but the aforementioned
front is decaying fast enough to suggest this will not occur.
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 4-5 ft
at 11 seconds. Guidance still suggests seas peaking around 8-9 ft
at 12 to 14 seconds late Saturday night due to a combination of
increased northerly wind waves and westerly swell.

Conditions will once again settle late Sunday into 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. -TK/Muessle

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...None.

&&

$$

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