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000
FXUS66 KPQR 201026
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
315 AM PDT Sat Apr 20 2024

.SYNOPSIS...Slightly cooler on Saturday as a cool front moves inland
later in the day. This front will bring increasing cloud cover and
spotty light rain Saturday afternoon and evening. Trending dry again
thereafter with mild conditions returning early next week, warmest on
Tuesday. Cool and showery conditions are likely to return late in the
week as an upper level trough settles over the area.

&&

.SHORT TERM...SATURDAY THROUGH MONDAY NIGHT...Satellite imagery from
early Saturday morning depicted clear skies across the region aside
from a few thin high clouds. Low-level offshore flow remained in
place with easterly winds gusting 20-30 mph over the far eastern
Portland metro. Winds were much lighter away from the western
Columbia River Gorge. Expect the east Gorge winds to continue through
Saturday morning before low-level flow rapidly transitions back
onshore in the afternoon. This is in response to an incoming cool
front, which will bring increasing cloud cover and some light rain
Saturday afternoon. QPF amounts are quite low given the weak and
fast-moving nature of the front, generally under 0.1" in the lowlands
and under 0.5" in the mountains. Expect high temperatures mainly in
the 60s, except upper 50s to lower 60s at the coast. High temps will
likely occur in the early afternoon before cloud cover thickens up
and the cool front arrives. The latest suite of CAM guidance suggests
light rain will begin around 11am-noon at the coast and around 3-5pm
across the interior lowlands from Kelso to Eugene. Forecast rain
amounts are lowest from Salem to Eugene at 0.01-0.03". Expect rain
will only last a few hours at any given location. Isolated
post-frontal showers will occur behind the front Saturday evening
into Sunday morning, mainly in the mountains.

A dry weather pattern returns Sunday afternoon into early next week
as low-level offshore redevelops and 500mb heights rise with an
incoming shortwave ridge. Sunday looks to be the coolest day with
highs in the 50s at the coast and low 60s inland. Warming back into
the upper 60s to lower 70s on Monday, except low to mid 60s at the
coast. Model spread via the NBM 1D Viewer is low, suggesting high
confidence amongst models and their ensembles in regards to the
temperature forecast. Overnight lows look to be a bit too warm for
widespread frost concerns at this time. However, cannot rule out some
patchy frost in the southern Willamette Valley/Eugene area and
outlying rural areas Sunday night as temps attempt dipping into the
mid 30s. The NBM is showing a 10-20% chance for temps below 35F from
Albany to Eugene, Corvallis to Junction City, and Salmon Creek to
Battle Ground. Probabilities fall below 10% for the rest of the
lowlands. -TK


.LONG TERM...TUESDAY THROUGH FRIDAY NIGHT...On Tuesday, the
GEFS/ENS/GEPS ensemble means all show southwest flow aloft across
western WA/OR on before 500 mb flow veers to the west on Wednesday.
The aforementioned wind shift is in response to a weak upper level
trough brushing the forecast area to the north. Models and their
ensembles suggest mainly dry weather for northwest OR and southwest
WA on Tuesday with low chances for light rain showers Tuesday night
through Wednesday night (10-20% chance in the lowlands, 20-40%
chance in the mountains). Temps look to be a bit above normal,
especially on Tuesday when there is a 60-90% chance for high temps
at or above 70F. In fact, the NBM is showing a 20% chance for high
temps near 80F over the Portland metro during a period of dry east
winds. This seems like a bit of a stretch as model soundings do show
fairly thick high clouds over the area that day, which will most
likely keep highs in the low to mid 70s.

Conditions will become noticeably cooler on Thursday as highs fall
back into the 50s across the area. This is in response to a cool
upper level trough that is set to move overhead late in the week,
bringing higher chances for rain. While NBM 6-hr PoPs only peak
around 50% in the lowlands, 24-hr PoPs peak close to 70%. This is
due to model timing differences. Only a very small number of
ensemble members are showing no rain at all, suggesting rain is
likely to occur at some point on Thursday and/or Friday. In
addition, the NBM is showing a 30-40% chance for 24-hr rain amounts
in excess of 0.25" across all of northwest OR and southwest WA,
except 40-60% in the mountains. -TK

&&

.AVIATION...VFR prevailing early this morning ahead of approaching
Pacific front. Expect the front to reach the coast around 18-21z
Sat, and push inland into the Willamette Valley around 21z Sat-00z
Sun. HREF guidance suggests a 60-80% chance that cigs fall to
MVFR along the coast during the frontal passage, and a 10-30%
chance for the Willamette Valley. This system will bring light
rain that is not expected to impact visibility. Expect winds to
turn westerly/southwesterly after 18z Sat with the frontal
passage, and strengthen to around 10-15 kt with gusts to 20-25 kt
at any given terminal through the afternoon.

Notes: The ASOS at KTTD is only available via the dial in option.
The AWOS at KMMV is still out of commission. As it is not
maintained locally by the National Weather Service, there is no
estimated time of repair.

PDX AND APPROACHES...VFR prevailing today and tonight, however cigs
lowering to low-end VFR early this afternoon with a 20-30% chance
for MVFR cigs around 21Z Sat to 00Z Sun. East winds around 8-12
kt continue through 18z Sat, then turn southwesterly in the
afternoon with the frontal passage. Southwest winds this afternoon
could gust between 20 and 25 kt.
/mh -Alviz

&&

.MARINE...Southerly winds increase through the day as the front
moves through the waters with Small Craft Advisory winds gusting
to 25 kt and choppy seas. The front moves ashore this afternoon
with westerly winds behind the front, the ease tonight into
Sunday as high pressure build over the waters. Northerly winds
return late Sunday as a thermal trough strengthens long the south
Oregon coast and northern California with winds gusting 20-30 kt
Monday and Tuesday.

Seas peak around 10 ft, mainly over the northern zones, this
afternoon. Seas gradually 6 to 8 ft Sunday through Tuesday but
will be choppy.
/mh


&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory from 11 AM this morning to 2 AM PDT Sunday
     for PZZ251-252-271-272.

     Small Craft Advisory from 11 AM this morning to 4 PM PDT this
     afternoon for PZZ253-273.

&&

$$

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