304
FXUS66 KPQR 301827 AAA
AFDPQR

Area Forecast Discussion...UPDATE
National Weather Service Portland OR
1126 AM PDT Sun Jun 30 2024

Update to Aviation discussion.

.SYNOPSIS...Light shower chances continue across the northern
portions of the CWA today. 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...Sunday through Tuesday...Upper level trough
continues moving over the PacNW today. Scattered showers
dissipated by late last night but are expected to return later
this morning into the afternoon as surface heating produces
enough localized instability. Showers will mainly be located
over the Coast Range and Cascades as orographic forcing will be
the main lifting mechanism for showers, but a few could meander
into the valley. NAM soundings show significantly less
instability for today than yesterday, so thunderstorm or heavy
shower chances are very limited with today`s scattered showers.

As the upper trough moves east Monday into Tuesday, ensemble
guidance continues to indicate strong ridging building over the
eastern Pacific with lower heights over the PacNW. This will
bring dry weather but will keep temperatures stable at right
around normal. Expect high temperatures for inland valleys in
the upper 70s to low 80s today through Tuesday with 60s along
the coast. -HEC

.LONG TERM...Wednesday through Saturday...The overall pattern
remains the same on Wednesday, according to the WPC 500 mb
cluster analysis, though the ridge axis looks to shift slightly
east over the Pacific which would allow widespread 80s for
inland valleys.

Thursday into Saturday remain a little uncertain as ensemble
members continue to struggle to handle the specifics of the
pattern. However, consensus in the WPC clusters is increasing on
either the upper ridge moving over the region or remaining close
enough to the region to warm temperatures into the 90s, though
the timing of the ridge moving inland remains uncertain. NBM and
LREF also agree with this scenario as both indicate around a
50-60% chance of temperatures reaching or exceeding 95F Friday
and Saturday for inland valleys, which would be the warmest
temperatures of the summer so far. NBM also indicates a 30-40%
chance of inland valleys reaching 100F at least one of those
days. It still needs to be mentioned that there`s a 5-15% chance
of a shortwave trough breaking through the ridge and approaching
the region Friday or Saturday, bringing stronger onshore flow
and lowering temperatures back to near normal. -HEC

&&

.AVIATION...A mix of VFR and MVFR inland late morning as
stratocumulus slowly mixing & dissipating. Expect to see VFR
prevailing after 20Z Sun or so. The VFR expected through most of
the night with a 20-60% chance for MVFR cigs after 12-14Z Mon
through about 18Z Mon. The higher chances from about KSLE to KEUG
and around the KPDX area. Coastal areas similar but with IFR cigs
and vis in the KAST area that appears to be associated with a
band of low clouds that extends offshore. The IFR at KAST expected
to lift by 20Z Sun as mixing increases. Late today into tonight
should see IFR cigs and vis return to the coast (80-90% chance)
from around 00-03Z Mon through 16-18Z Mon.

Will also see some shallow showers develop mainly over higher
terrain, but some of the showers from the Coast Range could drift
over the valley through this afternoon as some hires models
indicate.


PDX AND APPROACHES...VFR prevailing but expect brief MVFR cigs
around 2500 ft in the area through about 20Z Sun. VFR expected
through 18Z Mon, but there is a 40-50% chance for MVFR cigs
2000-3000 ft 13-16Z Mon.
/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 area of surface low
pressure will pass over the area today, supporting initially
southwest winds before turning to the west in its wake. Otherwise,
expect north to northwest winds across the waters as high pressure
strengthens toward the middle of next week, 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. A thermal low develops along the northern
California/southwest Oregon coast on Tuesday and
strengthening/spreading north into Wednesday and thereafter.
This will increase the pressure gradient along the coast and over
the waters with a >90% chance that northerly wind gusts of 20-30
kt spread northward across the waters by mid week. 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.

&&

$$

www.weather.gov/portland

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