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205
FXUS66 KPQR 290426
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
926 PM PDT Tue May 28 2024

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.SYNOPSIS...
After some light rain today and a few showers on
Wednesday, drier weather returns Thursday and Friday. A wetter
weather pattern returns over the weekend into early next week.

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.SHORT TERM...
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Now Through Friday...Water vapor satellite
imagery reveals a shortwave trough sliding into the Pacific
Northwest this afternoon. This has resulted in a weak front
approaching the I-5 corridor as of 2 PM. There has been just
enough surface heating ahead of the front and frontal forcing to
generate a few heavier showers along the front. With additional
surface heating behind the front and temperatures continuing to
cool aloft, a few more showers will develop across the area
this evening. An embedded shortwave trough sliding down the
backside of the parent shortwave trough will slide
southeastward, but mainly bypass the region by staying to our
north and east. Nonetheless, it should bring a reinforcing shot
of showers pushing onto the coast later tonight into Wednesday.

Ensembles systems are in good agreement shortwave ridging will build
into the Pacific Northwest Thursday into Friday. This will bring
drier weather and near to above average temperatures during this
period. /Neuman


.LONG TERM...Saturday and beyond...WPC Cluster Analysis shows there
is strong agreement that a weak shortwave trough will begin to take
hold across the Pacific Northwest on Saturday. There is good
agreement this will result in temperatures cooling on Saturday when
compared to Friday. The main uncertainty in the forecast on Saturday
revolves around the amplitude of the shortwave trough and
precipitation chances tied to a weakening front sliding towards the
region. Either way, any precipitation would be light.

Uncertainty in the overall pattern begins to grow on Sunday as the
remnants of Typhoon Ewiniar are ingested into the westerlies crossing
the Pacific. More on that in a minute. The majority of ensemble
guidance keeps us in zonal flow on Sunday, but our proximity to a
shortwave trough offshore does vary quite a bit between ensemble
members, which influences the amount of rain expected across the
region on Sunday and how far south it extends. Even then, there are
still 10-20% of the ensemble members that build a shortwave ridge
across the Pacific Northwest on Sunday and dry the area out entirely.

Farther out in time, 70-80% of the WPC cluster membership suggests
the shortwave trough digging over the northeast Pacific will remain
close enough to northwest Oregon and southwestern Washington to leave
the region susceptible to a moderate to strong atmospheric river,
particularly across the northern half of the CWA late Sunday into
Monday. While that may sound ominous, we see many moderate to strong
atmospheric rivers over the course of a winter season that bring only
beneficial rains to the region. This appears most likely to do the
same. Nonetheless, there are ~5% of the ensemble members that produce
enough QPF at places like Astoria or Portland that we are not 100%
out of the woods for potential impacts, particularly given many
reservoirs are near their summertime full pool levels and do not have
the flood control capacity that they do in the winter.

Finally, the CPC 8-14 day outlook does suggest a 60-70% chance for
above average temperatures between June 5-11th. While the map looks
ominously hot, average high temperatures are still only in the low
70s right now so a stretch of days in the 80s would count as above
average. There are still fewer than 20% of the ensemble members that
suggest temperatures climbing to near 90F or warmer late next week.
/Neuman
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.AVIATION...
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A cold front that passed through the are earlier today
now resides over eastern Oregon, leaving the region in a post
frontal environment. A majority of the shower activity has tapered
off across the interior valley as surface high pressure builds
into the area,. Winds have shifted to the north, bringing cooler,
drier air into the region. Shower activity has increased just
offshore between KNOP and KAST and may bring brief sub-VFR (or
lower) conditions to both of the terminals early tonight. Winds
will become light and variable overnight. Winds will pick back up
Wednesday afternoon from the W/NW along with shower activity
across the northern half of the CWA.

PDX AND APPROACHES...Conditions should remain VFR into Wednesday
as surface high pressure builds into the area. Light winds will
continue overnight, becoming westerly around 5-10 knots Wednesday
afternoon. Scattered showers will develop as daytime heating
increases. Confidence in any terminals being directly impacted is
low but could bring brief sub-VFR conditions. -Batz
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&&

.MARINE...
A weak front crossed the waters this morning, but has
produced few impacts. Weak high pressure will build across the
northeast Pacific Wednesday into Thursday and lead to increasing
northerly winds across the waters. The strongest winds will be off
the central coast of Oregon. For example, there is a >90% chance for
wind gusts in excess of 20 kt across those waters by Thursday
afternoon and evening. Most model guidance suggests winds will back
off a bit for Friday, but there is still a high probability (>75%
chance) wind gusts will climb above 20 kt across the waters off the
central coast of Oregon on Friday.

There is increasing agreement a more organized and stronger storm
system will move into the northeast Pacific over the weekend.
This will bring a high probability (>80% chance) for winds to turn
southerly and wind gusts to at least climb into Small Craft
Advisory thresholds of 25-30 kt. In addition, there is a 30-40%
chance for at least a brief period of unusually late season Gale
Force southerly wind gusts of 35 kt developing sometime Sunday into
Monday across the waters. Probabilities of this happening are
highest off the far north Oregon and south Washington coasts than
areas farther south towards Lane County. /Neuman

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...None.
&&

$$

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