337
FXUS66 KPQR 300457
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
957 PM PDT Sat Jun 29 2024

.UPDATED AVIATION DISCUSSION...

&&

.SYNOPSIS...
Aside from some light showers across the northern
portions of the CWA tonight into Sunday, onshore flow will
maintain near average temperatures into early next week. There is
50-60% chance that stronger high pressure offshore will shift
over the region towards the end of next week and bring the
hottest temperatures of the Summer so far.

&&

.SHORT TERM...Tonight through Monday...Water vapor satellite
imagery reveals a shortwave trough over the eastern Pacific
that`s knocking on the door of the Pacific Northwest. Some light
rain has begun to develop just offshore with some light rain
reaching the north coast near Seaside in just the last 1-2
hours. This precipitation appears to be forming in response to
mid level lift ahead of an embedded vorticity maxima that is
lifting northeastward towards southwest Washington.

In addition, KRTX doppler radar indicates a few surface based showers
have begun to pop over western Washington County and across the south
Washington Cascades despite limited SBCAPE in SPC mesoanalysis. These
showers and instability are supported by a
number of HREF members, though. While statistically the chance of any
given location receiving measurable rain this evening is probably
near the NBM`s 5-10% PoPs even if several of the HREF members were to
pan out exactly, opted to increase PoPs to 15-30% so that there is at
least some mention of rain showers in the forecast for the next
several hours. In addition, cooling temperatures aloft coupled with
surface heating will put us in the running for a short lived
thunderstorm or two, but the weak low to mid level flow will promote
most showers being rather short lived and keep thunderstorm chances
low.

Additional low level moisture and conditional instability will
promote rain chances continuing into Sunday across mainly the north
coast and Cascades from Lincoln and Clackamas Counties northward,
respectively. Otherwise, temperatures look to remain near average
into early next week. /Neuman


.LONG TERM...Tuesday through Saturday...WPC 500 mb cluster
analysis remains in very good agreement of upper level ridging
building over the Eastern Pacific early next week with generally
zonal flow over NW Oregon into SW Washington, leading to little
change in our sensible weather Tuesday into Wednesday. Ensembles are
in good agreement that inland areas will warm up on Thursday, but
there still remains some uncertainty in the magnitude of the warm up.

Uncertainty in the forecast grows further Friday into Saturday as
ensembles struggle to handle whether or not a shortwave trough
impinges on the region, the ridge builds and persists over the
Pacific Northwest or a shortwave trough near the Rockies persists
close enough to the region to keep temperatures in check. The most
likely scenario at this point is that high pressure aloft will remain
close enough to the region to keep hot temperatures in place. This is
supported by the NBM, which gives a 50-60% chance for the warmest
temperatures of the Summer so far developing next Friday and/or
Saturday. There`s at least a 30% chance that inland valleys even hit
100F one of those two days. The least likely scenario (around a
10-15% chance) is that we return to near or below average
temperatures Friday or Saturday as the aforementioned shortwave
trough drops southward towards the region and places the region under
stronger onshore flow. /Neuman

&&

.AVIATION...VFR prevails inland as a weak upper level disturbances
tracks across the region. Marine stratus has begun to settle into
the coast with a mix of IFR to LIFR cigs/vis already in place a
KAST and KONP. These should see gradual improvement through the
day Sunday with MVFR to low VFR conditions prevailing come the mid
to late afternoon hours. Inland VFR condition prevail most of
tonight with some mid and high clouds, but expected to see west
southwest flow at low and mid levels to spread marine clouds with
MVFR cigs inland roughly after 10-13Z Sun, then gradually
improving to VFR after 18-19Z Sun. The HREF projects a 60-80%
chance for CIGS at or below 3kft between 12-18z before the
aforementioned improvement finally takes place.

PDX AND APPROACHES...VFR prevailing through about 10Z Sun then
increasing chances for MVFR cigs 2000-3000 ft to develop. Chances
for MVFR peak at around ~70-18% 12-18Z Sun, then rapidly decrease
by 20Z Sun for high chances of VFR. -Schuldt/mh

&&

.MARINE...
Weak high pressure over the northeast Pacific with lower
surface pressure over California and the Great Basin will more or
less maintain itself into next week. A weak front will temporarily
clip the waters today and turn winds more out of the west. Tonight
into

Otherwise, expect north to northwest winds across the waters with
the strongest winds generally off the central coast of Oregon and
lighter winds farther north. Winds will generally peak in the
afternoon and evening hours each day. Pressure gradients appear
increasingly likely to increase by early to mid next week so that
there is a >90% chance that northerly wind gusts of 20-30 kt
spread northward across the waters. This will in return develop
steep wind driven seas of 5-8 ft with a dominant period of 7-8
seconds by late Tuesday or Wednesday. /Batz

&&

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

$$

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