337
FXUS66 KPQR 281803
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
1103 AM PDT Sun Apr 28 2024

Updated aviation section.

.SYNOPSIS...Cool onshore flow will continue over the next
several days. Embedded disturbances in the westerly flow aloft
will maintain showers, along with snow at times above 2500 feet
in the Cascades. Back to milder weather later this week, with a
dry day or two. Then, return to unsettled weather for next
weekend.

&&

.SHORT TERM...(Today through Tuesday)...Feels more like March
rather than late April across the region, with plenty of clouds
and showers. Zonal (westerly) flow off the Pac into the Pac NW
persists through Tuesday.

Next system will push across the region later today into this
evening. As such, will see showers increase in coverage and
intensity by afternoon. Still cool with temperatures staying in the
50s for the most part. Interestingly, main effect from this system
today will be to usher in bit cooler air aloft. This will allow for
instability to increase a tad, just enough to introduce a meager
possibility of thunder this afternoon into this evening. Does seem
that that potential will be over western Washington, and just
clipping far northwest Oregon. Models over past few days have been
back and forth on this potential, as to whether or not would be
there for today. But, based on current satellite and model trends,
can not ignore it. So, will maintain a slight chance (10-20%) for a
thundershower later today into this evening.

As cooler air aloft spreads inland tonight, will see snow levels
lower a bit more, settling around 2500 ft late tonight into Monday,
but down to 2000 ft over the Washington Cascades. While snow
accumulations are below standard criteria, it is late season and
with most cars no longer have snow tires or studded tires, will
maintain the current winter weather advisory. Accumulations
generally in the 2 to 8 inches range tonight, with the higher
accumulations being in areas above 4000 ft.

Not much change for Monday, as will see plenty of showers across the
region. Should see some breaks in the cloud cover for the afternoon.
Air mass still remains cool aloft, enough to maintain that small
chance of thundershowers, especially along the coast over the Coast
Range/Willapa Hills into the interior. Snow continues at times in
the Cascades. But, accumulations will vary thanks to showery nature
of the precipitation. Likely another 2 to 8 inches in the Cascades.

Yet another system arrives on Tue. This will be a bit stronger,
enough so could see couple of hours of steady light rain for a time
Tue morning as the low pushes into western Washington. Otherwise,
another showery day, with uptick of south to southwest winds. Ahhh,
April showers bring the May flowers.          /Rockey

.LONG TERM...(Wednesday through Friday)...Overall confidence is
low to moderate as the pattern stays rather progressive into
late next week. Deterministic and ensemble guidance continue to
struggle to resolve the longitudinal placement of ridge/trough
features going forward. 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. Thursday and beyond, 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 and becoming most
defined Friday.

&&

.AVIATION...Scattered showers continue across NW Oregon and SW
Washington through the TAF period as a weak front moves through
the region. Ceilings will hover around low-end VFR and high-end
MVFR, with showers occasionally lowering ceilings and
visibilities. Chances of widespread MVFR ceilings increase along
the coast after 23z Sunday and inland around 06-10z Monday,
raising around 18z Monday. Mountains are expected to remain
obscured through the TAF period. West to southwest winds through
the TAF period with gusts up to 20 kts along the coast.

There`s a 15-20% chance of thunderstorms after 20z Sunday
starting for locations along and north of the Columbia River
including the PDX metro area. The thunderstorm chances shift to
the entire northern Oregon and southern Washington coast after 06z
Monday, then expand across the entire forecast area after 15z
Monday. Current confidence in thunderstorms occurring at any
single terminal are too low to include in TAFs at this point.

Notes: The ASOS at KTTD is only available via the dial in option.
The AWOS at KMMV is still out of commission, but a tentative work
around has been implemented. There is no estimated time of
full repair and restoration for either of these locations.

PDX AND APPROACHES...Mixture of low-end VFR and high-end
MVFR conditions with scattered showers through the TAF period.
Slight chance (15-20% probability) for thunderstorms 20Z Sunday
through 06Z Monday, returning again after 15z Monday. Southwest
winds 9-13 kts with gusts to 15-18 kts. -HEC

&&

.MARINE...Active weather is expected to continue this weekend
an into the start of the week. A surface front moving through
the waters this evening will bring another round of elevated
winds along with steep and choppy seas. Therefore have issued a
series of small craft advisories through at least Monday
afternoon. Generally westerly winds through this time with gusts
up to 25 kt and seas of 6 to 9 ft at 10 to 13 seconds through
Monday.

A series of weak fronts will move through the waters this week
bringing elevated winds and seas at times. Some models are
suggesting that small craft conditions could develop with each
frontal passage, will continue to monitor the situation as it
develops. /42

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory from 8 PM this evening to 11 AM PDT
     Monday for ORZ126>128.
WA...Winter Weather Advisory from 8 PM this evening to 11 AM PDT
     Monday for WAZ211.
PZ...Small Craft Advisory until 5 PM PDT Monday for PZZ210-251>253-
     271>273.
&&

$$

www.weather.gov/portland

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