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000
FXUS66 KPQR 130454
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
954 PM PDT Fri Apr 12 2024

Updated aviation discussion

.SYNOPSIS...Mainly mild and dry conditions across the north,
with scattered showers lingering over the Cascades and south
Willamette Valley through Saturday as low pressure impacts
northern California. A few thunderstorms are possible mainly
along the Cascades Saturday afternoon. Mild and less showery
weather expected for Sunday, then cooler and wetter into the
beginning of next week as another system approaches from the
northwest.

&&

.SHORT TERM...Through Sunday Night...Early morning clouds and
drizzle have given way to plenty of sunshine across much of
northwest Oregon and southwest Washington this afternoon, with
temperatures climbing well into the 60s at many locations. A
deep upper level low is noted off of the northern California
coast, and this will remain the primary feature of interest in
terms of our weather into this weekend. Visible satellite
imagery shows mid and high level cloud cover streaming back over
the Cascades and South Willamette Valley in southerly flow on
the periphery of the low, with a few embedded showers noted on
radar. Mainly expect these hit or miss showers to remain south
and east of a roughly Mt Hood to Salem to Newport line through
this evening, with minimal associated precipitation. Can`t rule
out a rumble of thunder or two in the Lane County Cascades
through early this evening, but for the most part expect any
thunderstorm activity to remain east of the Cascades.

Temperatures trend upward on Saturday as the upper low begins
to shift inland over California and mid to upper level flow
takes on more of an offshore component across the Pacific
Northwest. This should help temperatures rise into the low to
mid 70s across the interior valleys, though the coastal
communities will likely stay moderated by the marine layer as
low level flow remains onshore. The primary forecast concern for
Saturday will be a chance for showers and a few thunderstorms
across the Oregon Cascades and perhaps southern parts of the
Willamette Valley Saturday afternoon and evening as wrap around
moisture continues to stream into the area on the northern
periphery of the low. Models depict precipitable water values
around rising to 0.8-0.9 inches by Saturday afternoon, which
would would fall roughly in the 90-95th percentile of
climatology by mid April standards and could support locally
heavy rain with some showers. Daytime heating will yield most
unstable CAPE values around 300-500 J/kg along the Cascade
crest, with enough bulk shear on the order of 20-30 kt to
support a few potentially strong thunderstorms along the crest
from roughly Mt Jefferson southward through Saturday evening.
Steering flow will be such that any storms that do develop could
drift over the southern half of the Willamette Valley with
time, but these storms would be likely to weaken as they
encounter a less favorable environment with westward extent.

Temperatures will begin to trend cooler on Sunday as onshore
flow returns to the region with the departure of the California
upper low into the Great Basin. Temperatures will still likely
make it into the mid to upper 60s across most of the area away
from the coast, with lingering shower activity along the
Cascades but no thunderstorms expected as more stable
conditions develop with onshore flow. /CB

.LONG TERM...Monday through Friday...Cooler and cloudier
conditions are expected Monday and Tuesday as another upper
grazes the region as it drops out of British Columbia into the
northern Rockies. Expect high temperatures to run a few degrees
below seasonal norms, generally in the mid to upper 50s both
days. There will be a chance for light rain both Monday and
Tuesday as the trough passes north of the region, but models
depict minimal QPF through this period as moisture will
generally be lacking. WPC ensemble clusters still show some
variation on the specifics of the pattern beyond Tuesday, but
all generally depict a warming and drying trend across the area
as the trough departs into the central CONUS and a ridge of high
pressure builds either over the eastern Pacific or directly over
the Pacific Northwest. This is supported by nearly all individual
ensemble members showing dry weather from Wednesday through
Friday of next week, with NBM 50th percentile guidance right
around 70 degrees each day. /CB

&&

.AVIATION...Southerly flow aloft tonight as a low pressure system
continues to spin off the central California coast, with high
clouds streaming north across the area. Predominately VFR expected
through the period, except for a 20-40% chance of MVFR conditions
developing at the coast overnight, and around a 20% chance of IFR
especially at KONP between 12-16Z Saturday. Flow aloft turns
southeasterly on Saturday with showers and possible thunderstorms
developing over the Lane County Cascades Sat afternoon, then
drifting northwest into the Willamette Valley. Predominately
north to northwest winds around 5-10 kt.

PDX AND APPROACHES...Expect predominately VFR with passing high
clouds through the period. There is a slight chance of showers
after 00Z Sunday. Northwest winds around 4-6 kt through Sat
morning. /DH

&&

.MARINE...A cut-off low continues to move toward California while
ridging across the northeast Pacific tries to build into OR/WA this
afternoon. This has tightened the surface pressure gradient across
the waters and will keep wind gusts in the 20-30 knot range for all
zones. A Small Craft Advisory remains in effect for all waters
through 2AM when the Columbia river bar will drop off followed by
the inner waters at 5AM. Wind gusts remain within advisory criteria
for the outer waters through Saturday and possibly longer, however,
confidence is low at this time. A NW swell at 7-9 feet persists into
Tuesday before relaxing to 4-6 feet around the middle of next week.
-Batz/Schuldt

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory until 2 AM PDT Saturday for PZZ210.

     Small Craft Advisory until 5 AM PDT Saturday for PZZ251>253.

     Small Craft Advisory until 5 PM PDT Saturday for PZZ271>273.
&&

$$

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