Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 292023

Area Forecast Discussion
National Weather Service Portland OR
123 PM PDT Wed Jun 29 2022

.SYNOPSIS...Little change in the overall pattern next several days,
with decreasing strength of the onshore flow. Overall, temperatures
pleasant, with temperatures in the 60s on the coast, and upper 70s to
lower 80s inland. Next low pressure will arrive this weekend,
bringing increased onshore flow. This will bring more clouds, cooler
temperatures, and even some spotty showers. Pattern will hold into
early next week.


.SHORT TERM (tonight through SAT)...Marine clouds continue to break
apart and dissipate this afternoon, with last of the clouds to those
against the lower slopes of the Cascades, as well as along the coast
beaches and offshore. Temperatures rather pleasant, with 60s along
the coast and 70s inland.

This rather pleasant pattern will continue, albeit with a bit weaker
onshore flow for the next few days. Expect another round of low
clouds to the region later tonight into early Thu, mainly along the
coast and inland north. But, otherwise, onshore flow weaker, with
sunshine breaking out bit earlier. As such, will see temperatures a
tad warmer for Thu, with 60s along the coast, and upper 70s to lower
80s inland.

Next change in the weather will arrive on Saturday, as low pressure
slowly pushes off the north Pac into the Pac NW. While system is not
all that organized, it will boost the onshore flow. As such, expect
more clouds on Sat, with partly cloudy skies in the afternoon. Can
not rule out a few showers, so will keep minor PoPs in for such. Main
effect will be bit cooler temperatures with clouds.  /Rockey

.LONG TERM...Saturday night through Tuesday...Forecast models show
good agreement that a broad upper level trough will dominate the NE
Pacific Saturday through Tuesday, with 500 mb heights mostly in the
lower to mid 570 decameter range. This would keep our forecast area
under southwesterly flow aloft, with a general continuation of the
seasonably warm and mostly dry weather expected for the remainder of
this week. The best chance of showers appears to be this weekend,
when a portion of the upper trough detaches and lifts NE into
southern BC. This may provide enough instability for showers, with
the best chance over the Cascades. Will not put any thunderstorms in
the forecast, as seems best instability combined with upper flow
would favor areas east of the Cascades for any afternoon/evening
thunderstorms on Sun and Mon.


.AVIATION...00z TAFs: MVFR ceilings linger along the coast at 20z,
but elsewhere VFR have taken over as surface heating caused the
stratus to quickly dissipate. VFR is expected to overtake most of
the coast over the next couple hours, with a return to MVFR
spreading back in around 04-06z Thursday.

Inland, VFR will continue a bit longer, but MVFR has a 60-80% chance
of returning to two large areas tonight after 09z. The first will be
in the northern Willamette Valley and adjacent southern Washington,
where onshore flow through the Columbia River Valley will encounter
the Cascades, resulting in an orographically forced ceiling which
will build westward - possibly to/beyond I-5 - throughout the early
morning Thursday. The other area of MVFR conditions will be across
the southern Willamette Valley, where northerly, upslope flow will
result in a deck of stratus which will slowly expand northward
throughout the morning. As was the case today, the onset of surface
heating will cause these thin stratus decks to vanish quickly
between 18z and 20z.

For detailed Pac NW aviation weather information, go online to:

KPDX AND APPROACHES...VFR conditions should continue through at
least 12z, when guidance begins to increase the chances for MVFR
ceilings at the terminal. The chance for these ceilings has come
down a little since the 18z TAF package issuance, but it still
appears there`s around a 40-50% probability for these ceilings
between roughly 13z and 17z. After that time, mostly clear skies
should quickly return with solar heating. -Bumgardner


.MARINE...Buoy observations at 1 PM Wednesday afternoon show seas of
4 ft at around 8 seconds, with northwest winds around 5 to 10 kt.
Winds will increase a bit in the afternoons Thursday through
Saturday as a thermal low builds across southern Oregon. However,
Small Craft Force wind gusts of greater than 20 kt are not expected
at this time. Seas will generally hover in the 4 to 5 ft range,
being driven mostly by wind waves with a background long-period,
southwesterly swell of 1 to 2 ft.

The area of high pressure over the eastern Pacific will slide south
and east towards us over the weekend, and on the north side of that
system our winds will ease and turn westerly as the coastal thermal
trough moves inland. The potential exists for a low to bring
southerly winds to our waters early next work week, but uncertainty
is vast in the details surrounding its evolution at this time. -

For more information about upcoming marine zone changes, go
online to:





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