664
FXUS66 KPQR 290933
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
233 AM PDT Sat Jun 29 2024

.SYNOPSIS...Aside from some light drizzle across the northern
portions of the CWA late Saturday into Sunday, onshore flow will
maintain near average temperatures into early next week. There is
40-60% 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...Saturday through Monday...Satellite data early
Saturday morning shows mid to high level clouds pushing into NW
Oregon and SW Washington as a broad upper level trough
approaches the coast. Latest guidance now shows two distinct
shortwaves pulsing through the PacNW with this trough, one later
this afternoon or evening and the second tomorrow. These
features will produce a 15-20% chance of light drizzle or rain
showers at times this afternoon through tomorrow morning, mainly
along the coast and Coast Range north of a line extending
between Mt Jefferson and Newport as well as the Cascades into
central Oregon. There`s not much cold air aloft with this
system, so temperatures this weekend into early next week will
remain right around normal for this time of year, even on Monday
as the upper trough moves to the east. This equates to upper 70s
to right around 80 degrees for inland valleys and 60s along the
coast. -HEC

.LONG TERM...Tuesday through Friday...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 the forecast for Tuesday.

Uncertainty in the forecast begins to grow dramatically midweek as
ensemble members begin to diverge substantially on potential
scenarios. While nearly all of the ensemble guidance has above
average 500mb heights over the Pacific Northwest by Thursday, about
25% of the ensemble guidance suggests an upper level trough will
either be approaching the region from the northwest or a different
shortwave trough will be lingering across the northern Rockies to
keep temperatures across the area near average. The rest suggest a
pattern conducive for above normal temperatures but with
varying degrees of heat. Latest NBM probabilities have risen for
temperatures reaching 90F across inland valleys with a 40-60%
on Thursday and 60-75% on Friday. Probabilities for reaching
100F on Friday have also risen to 30-45% for inland valleys.
The NBM deterministic forecast is on the warm side of the
probability distribution come next Friday, but not enough to
change it so have left the forecast as is. However, it`s
important to note that the forecast temperature spread is very
wide with mid 80s at the 25th percentile and low 100s for the
75th percentile distributions. -Neuman/HEC

&&

.AVIATION...High pressure continues to shift eastward as a weak
upper-level trough approaches from the west and crosses the region
late Saturday afternoon into the overnight. VFR conditions will
prevail everywhere through 20Z or so when MVFR or lower CIGs move
in along the coast as the weak disturbance moves eastward. HREF
and MOS guidance suggest low end VFR to high end MVFR CIGs
developing inland around 2000-5000 feet after 6Z Saturday night.
HREF probabilities within the Willamette Valley are 30-60%, so
still some uncertainty but still possible. A few light showers
will also be possible Saturday night, mainly along the coast and
north of the metro. Light north winds at 5 kts or less will become
west/northwest at 10-15 kts today.

PDX AND APPROACHES...High pressure shifting eastward will continue
to support VFR conditions through most of the day. Winds will be
north/northwesterly becoming more westerly at around 10 kts. CIGs
will gradually begin to drop as an upper level disturbance passes
overhead. VFR conditions are expected to prevail through around 6Z
Sunday when MVFR CIGs will be possible (40-70%). -Batz

&&

.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
try to clip the waters today and turn winds more out of the west.
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. /Neuman/Batz

&&

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

&&

$$

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