609
FXUS66 KPQR 221817 AAA
AFDPQR

Area Forecast Discussion...Updated
National Weather Service Portland OR
1112 AM PDT Sat Jun 22 2024

Updated aviation/marine and added beach hazards section.

.SYNOPSIS...After another hot day for inland valleys on Saturday,
cooler temperatures will return Sunday into Monday as onshore flow
strengthens. Conditions will remain mostly dry through Tuesday aside
from areas of light rain and drizzle Saturday night into Sunday
morning for the coast, west slopes of the Coast Range and Cascade
foothills. The eastern Portland metro may see a little light rain as
well, but confidence is low. Precip chances become more widespread
Wednesday into Thursday as an upper level trough moves inland, which
will also bring the return of cooler temperatures.

&&

.DISCUSSION...SATURDAY THROUGH FRIDAY NIGHT...Satellite imagery from
early Saturday morning revealed clear skies across the region aside
from a few passing high clouds. The exception was along the coast
from Coos Bay to Tillamook where a low marine stratus deck was in
place. However, the HREF suggests this stratus deck will scatter out
later this morning and bring mostly sunny conditions to the coast
before low clouds return to the coast late Saturday
afternoon/evening. As such, another cool day is in store for the
coast with highs in the 60s. With plenty of sunshine inland and very
little change to the weather pattern, expect another warm day with
high temps in the mid to upper 80s. Cannot completely rule out highs
of 90 degrees or warmer as the NBM is showing a 20-40% chance from
Salem to the Portland metro. However given observed surface temps
over the past two days have been in the upper 80s/lower 90s for most
inland valley locations and 850 mb temps on Saturday are 1-2 deg C
cooler, highs in the mid to upper 80s seems spot on. This is also in
line with the deterministic NBM, which has verified very well over
the past couple of days.

Beyond Saturday, models and their ensembles continue to depict
strengthening low-level onshore flow and increasing low-level
moisture Saturday night into Sunday as a weak cold front and
attendant upper level shortwave reach the coast. The latest suite of
hi-res model guidance shows light rain or drizzle beginning at the
coast/west slopes of the Coast Range Saturday evening before
expanding into the Cascade foothills and eastern Portland/Vancouver
metro Saturday night/early Sunday morning. NBM PoPs remain too low
based on ensemble guidance, forecast soundings, and the overall setup
in place (moist westerly upslope flow with saturated conditions in
the boundary layer; it still appears the marine layer will deepen to
1-1.5 km according to NAM/GFS soundings). Therefore decided to
increase NBM PoPs by blending in CONSAll guidance. In addition to the
light drizzle/light rain in the aforementioned areas, expect
expansive cloud cover Sunday morning across nearly all of northwest
OR and southwest WA. With the increase in cloud cover/stronger
onshore flow, Sunday will be cooler with highs most likely in the low
to mid 70s across the interior lowlands (except 60s at the coast).
Cannot completely rule out highs in the lower 80s if morning cloud
cover scatters out quickly enough, but the probability of this
occurring has decreased to 1-5%.

Less cloud cover on Monday, but still seasonable with highs in the
60s at the coast and 70s inland. A very brief warm-up is still in
store on Tuesday as a transient shortwave ridge passes through the
region, sending high temps back into the 80s for inland valleys. The
warmest ensemble members show high temps near 90 degrees over the
Willamette Valley, however the chance of this occurring is around 10%
or less. Even if some areas do briefly warm to 90 degrees Tuesday,
conditions will most definitely trend cooler Wednesday into Thursday
as an upper level trough over the northeast Pacific moves into
western WA/OR. This trough will also bring a chance of rain, however
confidence is low regarding the exact timing and exact rain amounts
given the large degree of model spread evident. NBM 6-hr PoPs
currently peak on Thursday between 20-60%, lowest from Florence to
Eugene to Oakridge and highs across southwest WA. The probability for
24-hr rain amounts in excess of 0.25 inches (from 5pm Wednesday
through 5pm Thursday) is at 10-30%, except less than 10% to the south
of Salem, south of Lincoln City, and east of Eugene.  -TK

&&

.BEACH HAZARDS...Low pressure approaching Haida Gwaii this morning
appears to be taking a track which supports a weak dynamic fetch to
build swell and aim it toward the Pac NW coast. This swell will
spread across the coastal waters Sunday, especially Sunday afternoon
and evening. Given the warm weather inland this weekend which will
likely lure people toward the beaches, have some concern for the
increased risk of sneaker waves Sunday. Will highlight this on social
media, but this is a marginal case so we will likely refrain from
issuing a Beach Hazards Statement for this event.  Weagle

&&

.AVIATION...As of 1730z, conditions were primarily VFR inland with
areas of IFR/MVFR along the coast. Overall, these general
conditions should prevail through this evening. Weak cold front
is approaching the coast and will deepen the marine layer, likely
leading to areas of coastal drizzle this evening (best chances
between 00z-06z). Strong onshore push will occur this evening with
gusts 20-25 kt likely through gaps in the Coast Range. Eventually
this will cause stratus to develop along the Cascade foothills
then backbuild into the Willamette Valley, with increasing chances
of MVFR later in the evening. By 08z, latest high-res forecast
models suggest greater than a 70-80% chance of MVFR cigs for the
Willamette Valley terminals east of I-5 (i.e KPDX, KTTD, KSLE,
KUAO, etc). Suspect this is about accurate for cigs in general,
but cig heights may end up just above 030 for some of this area.
With onshore flow persisting into Sunday and the moist layer
considerably deeper than today, clouds should linger well into the
day. Isolated showers are not out of the question over the Coast
Range and Cascades Sunday.

PDX AND APPROACHES...VFR with mainly clear skies and light onshore
flow today. W-NW winds will increase considerably after 22/23z-24z,
with sustained winds 10-15 kt and gusts up to 25 kt between
23/00z-08z. Winds will gradually decrease thereafter. Backbuilding
stratus from the Cascade foothills will lead to a 70-80% chance
of cigs by 23/10z, but chances of MVFR are closer to 50%. Cigs
that develop will persist well into the day Sunday.  Weagle

&&

.MARINE...Low pressure near 1000 mb was approaching Haida Gwaii
Sat morning, pushing a weak cold front across the Pac NW coastal
waters later today. Trajectory of low pressure does suggest a weak
dynamic fetch which could push seas up close to 10 ft Sunday
afternoon and evening. That said, the odds of seas reaching 10 ft
are too low (20-30%) to warrant a Small Craft Advisory at this
time. Otherwise, high pressure will expand across the waters
Sunday and Monday while thermal low pressure strengthens over the
Sacramento Valley and near the OR/CA border. This will lead to
moderate N-NW flow early next week, with about a 30-40% chance of
wind gusts exceeding SCA criteria of 21 kt Monday afternoon.
Weagle


&&

.PQR WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

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