516
FXUS66 KPQR 292225
AFDPQR

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


.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 instabilty 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 prevailing ahead of upper level trough and weak
frontal system approaching the coast. The front is expected to
bring MVFR conditions to the coast around 22z Sat to 03Z Sun.
Behind the front, marine stratus will settle on to the coast with
a high likelihood (80-90%) of IFR conditions from about 03Z-12Z
Sun with a few hours of 40-60% chance before and after. Conditions
gradually improve through the day with MVFR conditions
prevailing. Inland VFR condition prevail with some 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 18Z Sun.

HIRES models show some discrete showers developing in the north
coast range and possibly moving into the north Willamette Valley
through early this evening.


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 60-70% 14-18Z Sun, then rapidly decrease
by 21Z Sun for high chances of VFR. HIRES models show some
discrete showers developing in the north coast range and possibly
affecting KHIO, KPDX/KTTD area 23 Sat-02Z Sun. /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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