180
FXUS66 KPQR 121839
AFDPQR

Area Forecast Discussion...Updated Aviation
National Weather Service Portland OR
1138 AM PDT Sun May 12 2024

.SYNOPSIS...A shortwave trough will drop into the PNW Sunday
into Monday and will bring cooler temperatures to the region.
Onshore flow will support marine stratus pushing into the
Willamette Valley Monday morning. Ridging is expected to
redevelop by mid-week and will support an upward trend in
temperatures back into the upper 70s.

&&

.SHORT TERM...Now through Monday night...The upper level ridge
axis now sits southeast of the CWA through southern Oregon and
will continue to move southeast into the Great Basin through
today. A shortwave trough off the PNW coast will move onshore
late today into Sunday night. Flow aloft will become
west/southwest surface slow remains onshore from the northwest.
Marine stratus has developed along much of the south and central
Oregon coast and into the Coast Range Valleys. Stratus may try
to advance farther east into the Willamette Valley around dawn
but will struggle due to warmer temperatures. A few scattered
clouds may pop up but shouldn`t bring any impacts. Temperatures
will be 8-10 degrees cooler across the Willamette Valley,
peaking within a degree or two of 80. Temperatures along the
coast will be 3-5 degrees cooler, peaking in the low to mid 60s
after starting the day under stratus which should dissipate by
noon.

The cooling pattern will continue into Monday as the shortwave
trough axis passes over the Cascades Sunday night. Marine
stratus is likely to develop tonight, with a better chance of
reaching into the Willamette Valley as onshore flow increases.
Northwest flow aloft and onshore at the surface along with
marine stratus in the morning will keep temperatures Monday
afternoon much cooler. Low 70s are expected across the
Willamette Valley, probabilities of highs reaching or exceeding
75 degrees range from 10-30%. Highs along the coast will
struggle to make it out of the 50s though some of the valleys
along the Coast Range will reach into the 60s. -Batz

.LONG TERM...Tuesday through Saturday...WPC cluster analysis
continues to favor ridge re- development by the middle of next
week. Nearly all ensemble members display relatively strong and
broad ridging by Wednesday next week, allowing temperatures to
climb to the upper 70s in the latter half of the week. Agreement
lessens into Friday as there is a 20-30% chance of a trough
developing and pushing south into the region. This trough would
bring more seasonable temperatures and light rain showers back
to the area, but there is still not enough model convergence to
be certain. Cluster analysis looks to be at a 50/50 in terms of
a ridge vs trough developing into early next weekend, with
either a broad ridge remaining overhead or a shortwave trough
moving into the region. -JH/Batz

&&

.AVIATION...High pressure continues, with mostly clear skies
throughout the region. Some low stratus continues at the coast,
but daylight heating will ensure that it is short lived. Northern
coastal terminals continue to see MVFR countdowns, but these will
end within the next hour or two, by 20z Sun.

Onshore flow increases throughout the day, bringing marine stratus
back to the coast in the late afternoon/evening, around 00z Mon. C

High pressure remains over the region, maintain mostly
clear skies aloft. Thermal low pressure over the Cascades will
move further eastward today, with increasing onshore flow today
over much of the area. As such, IFR stratus along the coast will
persist into this am, with patchy IFR stratus inland.Stratus will
break apart and dissipate later this am into the afternoon, but
may persist close to the beaches. Conditions look to remain mostly
low-end MVFR at the coast, though IFR conditions are possible
(40-50%) in the latter half of Sunday night. Further inland,
stratus clouds push in around 07-09z Mon, with a 80-90% chance of
MVFR ceilings developing at that time.

PDX AND APPROACHES...VFR with clear skies for the rest of daytime
hours. Marine clouds push in overnight, with MVFR CIGS developing
around 09z Mon. Only around 10-20% chance of ceilings reaching IFR
thresholds at that time. /JLiu

&&

.MARINE...A summerlike pattern will persist through early next
week as high pressure offshore and thermal low pressure shifting
farther inland maintain moderate to strong northerly breezes for
the next several days. Gradients will tighten just enough to
allow winds to gust to 25 kt across the waters this afternoon,
supporting low end Small Craft Advisories through late this
evening. Winds will continue to follow a diurnal trend for the
next few days, with additional rounds of small craft headlines
possible each afternoon and evening. Seas will generally remain in
the 4-6 ft range driven by northerly wind waves and a modest
westerly swell.    /CB/CCR

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory until 11 PM PDT this evening for
PZZ251>253-
     271>273.
&&

$$

www.weather.gov/portland

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