713
FXUS66 KPQR 221713 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
1013 AM PDT Wed May 22 2024

Updated Aviation Discussion

.SYNOPSIS...A weather system today will bring additional breezy
winds, cooler temperatures, and scattered showers with less
rain accumulation than yesterday. Brief period of dry and warmer
temperatures Thursday before unsettled weather with scattered
showers continues Friday into Saturday. Mostly dry with warming
temperatures Sunday into early next week.

&&

.SHORT TERM...Wednesday through Friday...Surface observations as
of 1 AM Wednesday show the surface front that moved through the
forecast area on Tuesday is now located in eastern Oregon while
satellite data indicates that the incoming closed upper level
low pressure system is located along the Canada/Washington
border just east of Vancouver Island. Post-frontal scattered,
very light showers are visible on radar, mainly along the
mountains and their western foothills. The upper low will move
into Washington from the north over the early morning hours of
Wednesday before pushing southeast into eastern Oregon
throughout the rest of the day. Showers will pick up again later
this morning and mostly dissipate by the evening, with light
showers continuing over the Cascades through tonight. With the
northwestern flow, showers will be very isolated in the lowlands
with the majority of the precipitation over the Cascades.
Although the main cold core of the low is expected to miss our
area to the north and east, latest hi-res models indicate enough
cold air aloft will move over the area to produce around
100-250 J/kg of CAPE this morning and afternoon, mainly over the
Cascades and lowlands north of Salem. This likely won`t be
enough instability for thunderstorms except for potentially
along the western slopes of the Cascades if orographic lift is
enough to produce a lightning strike or two. However, expect
periods of moderate to heavy rain in stronger showers as well as
small hail. With the colder temperatures, snow levels are
expected to lower enough for snow to fall above pass level in
the Cascades. Also, expect breezy westerly winds as the low
passes with gusts up to 20-25 mph, except up to 35-40 mph over
the high Cascades and Columbia River Gorge.

Shortwave ridging returns Thursday as the closed upper low moves
east into the northern Rockies. This will bring dry weather,
mostly sunny skies, and warmer temperatures. Temperatures are
forecast to rise to the upper 60s in the interior lowlands with
only a 10-25% probability of temperatures reaching 70 degrees.

Ensemble guidance is in good agreement that an upper shortwave
and surface front will move through the PacNW Friday, bringing
additional scattered showers in the late morning through evening
hours. These will be pretty weak and lacking much moisture and
forcing, so once again, limited precipitation is expected in
the lowlands with only about 0.1-0.25 inches of rain over the
Cascades through Friday night. -HEC

.LONG TERM...Saturday through Tuesday...WPC 500 mb cluster
analysis indicates another weak trough will move through the
PacNW on Saturday, though the depth of the trough and therefore
precipitation amounts are still uncertain. Overall, even on the
higher end of ensemble guidance, precipitation amounts look
pretty similar to Friday`s precipitation with limited amounts in
the lowlands and slightly higher over the Cascades and Coast
Range.

On Sunday, the majority of 500 mb clusters indicate either
zonal flow or slight ridging returning to the PacNW. This will
bring dry weather except for the potential for some lingering
showers over the northern counties of Oregon and SW Washington
counties if more zonal flow continues.

By Monday and Tuesday, clusters indicate ridging continues to
build over the Western US, though exact amplitude and location
of the ridge is still a little uncertain. This would still bring
mostly dry and warmer conditions to NW Oregon and SW
Washington, though just how warm is the question. The NBM spread
for the 25th and 75th percentiles along the inland valleys is
anywhere from upper 60s to low 80s. Latest NBM deterministic and
median temperature forecasts puts temperatures in the low to mid
70s. -HEC

&&

.AVIATION...Widespread VFR across the airspace. Given the post
frontal environment, expect showers along with a 30% probability
MVFR conditions. MVFR conditions will likely be associated with
precipitation. Predominant CIGS will fluctuate between 3500-5500
ft. Mountains will likely remain obscured. If flying into western
Oregon and Washington, gravity waves have been observed east of
the Cascade crest. MVFR conditions likely to become the dominant
flight category along the coast around 03Z Thursday.

Northerly to westerly winds with gusts up to 25 kt possible at
all terminals through around 00Z Thursday.

PDX AND APPROACHES...Widespread VFR with postfrontal showers. CIGs
expected to fluctuate between 3500-5000 ft with a 20%-40%
probability for intermittent MVFR conditions that will likely be
associated with passing showers. Westerly winds with gusts up to
20 kt through around 00Z Thursday. /42

&&

.MARINE...Northwesterly flow in the post-frontal environment will
continue to produce breezy winds today with gusts around 20-25
knots common place across the coastal waters. This morning a sharp
rise in seas is also anticipated with the arrival of a fresh
northwesterly swell peaking around 10-13ft at 9-10 seconds across
waters mainly north of Cape Falcon. Fortunately, the southern
waters shouldn`t see nearly as much of a rise but waves will still
remain fairly steep. Thus the current Small Craft Advisory
continues until this afternoon/evening as winds and seas stay
elevated. The upper-level low responsible for the active
conditions departs Wednesday night into Thursday accompanied by
calmer winds/seas returning for a brief period of time. Yet
another weather disturbance swings into the region from the NNW
the second half of Friday through Saturday continuing the rather
progressive and active weather pattern. Seas likely rise to 7-9
feet at 8-9 seconds on Saturday before decreasing to 4-5 feet at 9
seconds Sunday into early next week. -Schuldt

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory until 5 PM PDT this afternoon for PZZ210-
     251-252-273.

     Small Craft Advisory until 8 PM PDT this evening for PZZ271-272.
&&


$$

www.weather.gov/portland

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