868
FXUS66 KPQR 231555
AFDPQR

Area Forecast Discussion UPDATED
National Weather Service Portland OR
855 AM PDT Sun Jun 23 2024

...MORNING update, for aviation weather...

.SYNOPSIS...Cooler and cloudier on Sunday with drizzle or light rain
at the coast, western slopes of the Coast Range, Cascades and eastern
Portland/Vancouver metro. Dry on Monday with seasonable temperatures.
A transient shortwave ridge will bring a brief warmup on Tuesday
before an upper level trough brings relatively cooler temperatures
Wednesday through Thursday along with periodic chances for rain
showers. Trending slightly warmer again next weekend.

&&

.DISCUSSION...SUNDAY THROUGH SATURDAY NIGHT...Satellite imagery from
early Sunday morning depicted mostly cloudy skies across northwest OR
and southwest WA due to a marine push. In addition to the extensive
cloud cover, areas of drizzle were being observed at the coast and
portions of the Cascade foothills. This trend will continue through
Sunday morning, with light drizzle potentially impacting the
Camas/Troutdale area into the western Columbia River Gorge as well.
Otherwise expect a mix of sun and clouds Sunday afternoon with high
temperatures in the low to mid 70s across the lowlands, except upper
50s to mid 60s at the coast.

Dry conditions will prevail across the region on Monday with plenty
of sunshine and seasonable temperatures. Overall Monday looks to be a
great day for outdoor activities. Heating up again on Tuesday as a
shortwave ridge moves inland, however models and their ensembles
continue to suggest this ridge will be fast-moving as an upper level
trough over the northeast Pacific approaches the Pacific Northwest.
With this pattern in place, Tuesday will be the warmest day of the
week with highs temps well into the 80s from Vancouver to Eugene,
Portland to Hood River, and in the Cascade valleys. Cannot completely
rule out high temps in the lower 90s in these areas as the
probability for high temps of 90 degrees or warmer is around 5-15%.

Despite the warmer temps on Tuesday, the aforementioned upper level
trough will bring a quick return to cooler temperatures for Wednesday
and Thursday with high temps in the low to mid 70s and 60s at the
coast. This trough will also bring increasing chances for rain
showers. NBM 6-hr PoPs have increased a bit during that time but the
exact timing remains uncertain. Nevertheless, confidence is fairly
high that most locations in southwest WA and far northwest OR will
see at least some measurable rain on Wednesday and/or Thursday as
nearly every ensemble member from the GEFS/EPS/CMC show QPF at PDX,
albeit at different times. To help account for these timing
differences, it is likely better to message 24-hour PoPs rather than
6-hour PoPs to ensure the probability does not appear misleadingly
low. For example, NBM 6-hr PoPs range between 15-60% while NBM 24-hr
PoPs range between 25-90% (highest over southwest WA and lowest in
the Eugene area).

After this trough moves through the region, models and their
ensembles are generally trending a bit warmer and drier Friday into
next weekend as weak ridging develops. Only one cluster on WPC`s
cluster analysis is showing a trough during that time, but this
cluster only makes up 13% of the total ensemble space and is mainly
driven by the cooler GEFS solution. Regardless of the outcome, there
are no signs of extreme heat or any impactful weather next weekend.
Enjoy!-TK

&&

.AVIATION...Moderate to strong onshore flow today, with considerable
clouds across the region. Overall, mix of higher end MVFR to lower
end VFR (CIGS 2500 to 3500), with cloud tops running near 4500 to
5000 ft. Clouds will hold into the afternoon, but will gradually
break apart today, with VFR for most areas under SCT-BKN CIGS along
the coast. As low level flow turns more north to northeasterly later
today into this evening, will see clouds clear, primarily along the
coast from Newport southward, and inland to south and east of Salem.

PDX AND APPROACHES...Moderate to strong onshore flow will maintain
marine clouds across region into the afternoon. Though will have a
few holes in the cloud deck, am not expecting much in way of
clearing until after 22Z. Should remain VFR with scattered clouds
afterwards, with same conditions continuing overnight. Likely to
see areas of MVFR (CIGS 2500 to 3000 ft) reform late tonight into
early Monday am, especially to east and north of field.  /Rockey

&&

.MARINE...Low pressure around 1010 mb near Haida Gwaii Sun
morning with high pressure to the southwest. The resulting wind
field suggests a weak dynamic fetch which could generate seas
higher than forecast. But as of 3 am Sunday wave models are within
1 ft of buoy observations. Though the coastal waters will see
westerly swell build this afternoon will be in the 7 to 9 ft
range.

Otherwise, high pressure will expand across the waters through Monday
while thermal low pressure strengthens over the Sacramento Valley
and near the OR/CA border. This will lead to moderate N-NW flow
through Tues, with about a 20-40% chance of wind gusts exceeding
SCA criteria of 21 kt Monday afternoon. This pattern weakens the
winds by mid-week as another low pressure system over the
northeast Pacific nudges closer to the Pacific Northwest. /mh
-Weagle

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...None.

&&

$$

www.weather.gov/portland

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