000
FXUS66 KPQR 270452
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
951 PM PDT Fri Apr 26 2024

Updated aviation discussion

.SYNOPSIS...Showery and unsettled conditions continue through
the weekend into next week as the Pacific Northwest remains
under the influence of a rather progressive spring-time weather
pattern. Beyond the more persistent chances for rainfall going
forward, snow levels are expected to fall as low as 2500-3000ft
on Monday with good chances(65-95%) light snow accumulation(>1")
across the the Cascades through Tuesday morning. Model uncertainty
increases significantly by the middle to end of the week,
however, latest runs continue to trend towards the potential(60%)
for at least a brief period of drier conditions centered around
Wednesday.

&&

.SHORT TERM...Tonight through Monday...The axis of the upper-
level trough overhead responsible for our ample shower activity
around the region this afternoon has begun shifting east into
the Cascades. Expect showers to gradually decreasing later
tonight, as the airmass begins to stabilize in response to weak
transitory ridge of high pressure currently offshore shifting
inland. That said, the arrival of fast moving frontal boundary
extending southward off a parent low located over the gulf of
Alaska increases chances for precipitation Saturday late morning
and afternoon.With the rather fast movement of this feature,
overall rainfall amounts will not be all that much with the NBM
still indicating around 0.10 to 0.25 inch, with heaviest along
the coast. As usual, bit higher amounts over the higher terrain,
with 0.25 to 0.50 inch in spots of the Coast Range/Willapa
Hills and Cascades.

Saturday night through Sunday we`ll return back to a cooler and
showery weather pattern under broad zonal flow. The airmass
filtering in aloft likely drives snow levels back around 4500ft
by Sunday afternoon although the timing of this decrease likely
means a lack of impacts for the Cascade passes, at least
initially - this changes come Monday. It`s worth mentioning
dropping upper-level temperatures and daytime heating has a
slight chance(15-25%) to produce convective showers robust
enough to produce a lightning strike or two Sunday afternoon as
indicated by deterministic model soundings. Come Sunday night
into Monday a quick moving upper-level shortwave trough races
into the Pacific Northwest accompanied by a cold- frontal
boundary leading to yet another increase in precipitation
chances and snow- levels lowering further by Monday morning to
2500-3000ft. While the current thinking is snowfall at this
elevation will largely be slush in the grass, if anything sticks
at all, higher locations around and above 4000ft including our
mountain passes have a much better chance(75-95%) to see wet
snow accumulation and potential minor travel impacts through
Monday night. -Schuldt

.LONG TERM...Tuesday through Thursday...Overall confidence is
low to moderate the pattern stays rather progressive into late
next week - deterministic and ensemble guidance struggle
resolving the longitudinal placement of ridge/trough features
going forward. Showers are expected to linger on Tuesday as snow
levels hold somewhere between 2500-3500ft. Wednesday guidance
has continued to trend a little drier nudging a larger scale
upper-level low further north while a transient ridge glides
over the region. Out of all the ensemble solutions available,
this scenario is present in roughly 60% of them in addition to
the latest deterministic ECMWF and GFS. Past this point model
uncertainty becomes truly significant with nearly a 50/50 split
between maintaining a ridge feature overhead or bringing a
potent trough into the region by Thursday. Hopefully in the
coming forecast runs guidance begins to show better agreement
resolving the pattern mid to late week. Current confidence in
the forecast by Thursday is low. -Schuldt

&&

.AVIATION...Showers decreasing this evening as will be in between
systems overnight. The majority of the night should generally see
VFR conditions inland and MVFR at the coast. Inland areas only
see around a 20-30% chance of brief MVFR ceilings overnight.
Expect to see more widespread MVFR (with IFR at the coast) as the
next front spreads rain into the area Saturday morning.

Notes: The ASOS at KTTD is only available via the dial in option.
The AWOS at KMMV is still out of commission. There is no
estimated time of repair.

PDX AND APPROACHES...Break in precipitation has allowed for mostly
VFR conditions at the moment. MVFR 20-40% chance of MVFR ceilings
between 08-16z. Afterwards, higher confidence (80%+) in MVFR
ceilings as the next front pushes in. /JLiu

&&

.MARINE...Post-frontal conditions persist resulting in steep and
choppy seas. Winds are slowly shifting southwesterly, with weaker
winds between 10 to 20 kts expected this evening. Winds will
briefly dip in the latter half of Friday night, and the Small
Craft Advisory for the rest of Friday will primarily be for steep
and choppy seas around 7 to 10 ft at 8 to 10 seconds. Winds will
begin rising again and turning southerly Saturday morning with
the next front. Gusts up to 25-30 kt will be possible throughout
Saturday daytime hours. Model guidance continues to decrease the
chance of gales on Saturday, and is currently <10%. /JLiu

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory until 8 PM PDT Saturday for PZZ210-251>253-
     271>273.
&&

$$

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