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000
FXUS66 KPQR 201835 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
1135 AM PDT Sat Apr 20 2024

Updated aviation discussion


.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 SUNDAY...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...Satellite shows the front just off of the coast which
will move in today. VFR stratus inland, while low-end MVFR
expected along the coast. Clouds will fill in from KONP northward
through the afternoon. Will say that this front has been fairly
slow and is decaying quickly as it reaches the Pacific Northwest.
Winds are yet again a forecast feature to watch as they will shift
from the currently easterly direction to a westerly onshore flow
by 00Z Sunday. Gusts will be highest along the coast, especially
with the bulk of the front, and in the early part of the TAF
package as the easterly flow persists inland. Rain will fall,
though with a very dry lower level atmosphere there is a chance
that the rain will fall as virga and evaporate. No concerns for
VIS with the rain.

One thing we are watching in the Willamette Valley is the
possibility for fog around KSLE and KEUG. It will greatly depend
on the presence of clouds in the evening and early morning. If
enough radiational cooling occurs, cannot rule out MIFG at those
terminals - though would be short lived.

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 decreasing
chances for MVFR CIGs. Latest high resolution models have backed
off of these lower CIG levels in the last run. East winds around
8-12 kt continue through 23Z Sat as the front is quite slow.
Southwest winds this afternoon could gust between 20 and 25 kt.
-Muessle

&&

.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 until 2 AM PDT Sunday for PZZ251-252-271-
     272.
     Small Craft Advisory until 4 PM PDT this afternoon for PZZ253-
     273.
&&

$$

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