261
FXUS66 KPQR 122122
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
222 PM PDT Sun May 12 2024

.SYNOPSIS...A shortwave trough will push through the Pacific
Northwest tonight into tomorrow (Monday), returning cooler
temperatures. As onshore flow increases, expect marine stratus
to return tonight to the coast and push inland to the Willamette
Valley. The shortwave trough will be weak, so precipitation is
not expected. High pressure ridging returns Tuesday-Thursday,
continuing warm, dry, and clear conditions. Uncertainty remains
with whether or not this trend continues over the weekend.

&&

.SHORT TERM...Tonight through Tuesday...The latest 500mb
analysis depicts an upper level ridge axis over the Great Basin
and Interior Northwest. As a result, satellite imagery as of
2 PM PDT show mostly clear skies across of northwest Oregon and
southwest Washington. Most of the marine stratus from this
morning has dissipated from the coast, however, some cloud cover
remains along the Long Beach Peninsula and far north Oregon
coast. Temperatures look on track to reach the upper 70s inland
and low to mid 60s along the coast this afternoon.

Tonight through tomorrow (Mon), an upper level shortwave trough
will push through the Pacific Northwest. This shortwave system
will be weak and mostly dry, so PoPs remain less than 5% across
northwest Oregon and southwest Washington. As onshore flow
increases, expect marine stratus to return tonight to the coast
and push inland into the Willamette Valley. We`ll also see some
high clouds move through the area during the day as the
shortwave progresses eastward. With the increased cloud cover,
afternoon highs tomorrow are forecast around 6-10 degrees cooler
than today. Expect highs tomorrow to peak in the low 70s for
inland valleys and upper 50s to low 60s along the coast and
higher terrain. The latest NBM shows a 15-25% chance of high
temps exceeding 75 degrees F in the Willamette Valley tomorrow.

On Tuesday, ensemble guidance are in agreement of upper level
ridging re-building over the Pacific Northwest. This will help
return clear skies across the region during the day, and thus
warmer afternoon temperatures. NBM shows a 40-70% chance of
Tuesday afternoon highs exceeding 75 degrees F in the Willamette
Valley (highest chances in the central and north Valley). A
thermal trough develops along the southern Oregon coast, but
doesn`t quite reach the central/north Oregon and south Washington
coast. As a result, we`re not looking at any strong east flow
developing, but rather more northerly to north-northeasterly
winds.       -Alviz

&&

.LONG TERM...Tuesday night through Saturday...WPC cluster
analyses are in agreement of upper level ridging continuing over
the Pacific Northwest through Thursday. This will maintain dry
and warm conditions under predominately clear skies. NBM suggests
a 50-70% chance of Willamette Valley highs exceeding 80 degrees F
on Wednesday, and a 40-50% chance on Thursday. About 60% of
ensemble members do have the ridge flattening slightly on
Thursday, so afternoon highs could be a few degrees cooler than
Wednesday.

Cluster agreement lessens on Friday as 50% of ensemble members
think we`ll maintain upper level ridging, while the other 50%
suggests more troughing/zonal flow. This uncertainty continues
through the weekend. If models trend toward a troughing/zonal
flow pattern, we`ll likely see temperatures cool and a slight
chance (15-24%) of PoPs over higher terrain. If models trend
toward keeping the ridge, then expect the forecast to maintain
warm, dry, and clear conditions.     -Alviz

&&

.AVIATION...High pressure continues, with mostly clear skies
throughout the region. Low stratus from the morning hours has
burned off, and clear skies are expected for the next few hours.
Onshore flow continues to increase, and marine stratus returns
to the coast around 00z Mon. Afterwards conditions look to
remain mostly low-end MVFR at the coast, though IFR conditions
are possible (40-50%) from around 06z Mon onwards.

Further inland, northern terminals will see stratus clouds push
in around 07-09z Mon, with a 80-90% chance of MVFR ceilings
developing at that time. Only around a 15% chance of IFR
conditions developing throughout the rest of Sunday night. Further
south (south of KSLE), marine clouds should not impact the area,
and chances of MVFR ceilings are under 10%.

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...The summerlike pattern continues through the middle of
the upcoming week, and the thermal low pressure shifts farther
inland to 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. Tuesday and Wednesday
afternoon/evening look a little stronger, with gusts up to 30 kt
possible. Chance of any winds reaching gale level is around 40%
for Tuesday and Wednesday. Seas will generally remain in the 4-6
ft range driven by northerly wind waves and a modest westerly
swell.   /JLiu/CCR

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

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

$$

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