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419
FXUS66 KPQR 300932
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
225 AM PDT Thu May 30 2024

.SYNOPSIS..Warm and dry weather today with a slight warming trend
through Friday. A weakening front pushes across the area on Saturday,
which will result in a slight cooling trend but generally remaining
dry. Then, a much wetter system associated with what remains of a
tropical system is expected Sunday through Monday. Warm and dry
weather returns for the middle of next week.

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.SHORT TERM...
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Today through Saturday night...High pressure gradually
builds across the region resulting in warm, dry weather along with
northerly flow across the forecast area. This ridge of high pressure
will be the dominant synoptic feature through Friday. Expect inland
temperatures into the 70s today and upper 70s with some areas likely
warming into the low 80s on Friday. Coastal locations and the
Cascades will remain cooler with highs in the mid 50s to mid 60s.
Saturday a pattern change is on deck as a broad upper level trough
and associated surface, cold front brings slightly cooler
temperatures as well as some very light precipitation to higher
elevations. A larger, more robust system will start to impact the
region Saturday night but the larger impacts are not expected until
Sunday. /42

.LONG TERM...Sunday through Wednesday...On Sunday the remnants of
Typhoon Ewiniar have been fully ingested into the models and are
under the influence of the westerlies crossing the Pacific. The
majority of ensemble guidance keeps us in slightly zonal flow or a
slightly troughy as a shortwave trough can be seen in some models. As
a result am leaning towards a cooler and wetter solution for Sunday
and Monday. In addition to the trough, models are also showing the
potential for a strong to moderate atmospheric river pointed towards
the Pac NW. 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. At
this time, storm total QPF values range from 1.00 to 1.25 inches
within the Willamette Valley, 1.30-2.50 inches along the Coast and
1.25-3.50 inches for the Cascades. It will not be out of the question
for higher elevations and area north of the Portland/Vancouver Metro
area to receive accumulations towards the higher side of these ranges,
with those areas that are north of the PDX/VUO areas and at a higher
elevation could see upwards of 3.00 to 4.00 inches when all is said
and done by Monday night.

Tuesday and into the latter part of next week, cluster guidance does
show a pattern change that will result in warmer and drier conditions
with daytime highs in the 70s on Tuesday with temperatures likely
climbing into the 80s by Thursday. /42
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.AVIATION...
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VFR conditions prevailing across the area with
generally clear skies. Expect VFR through 12Z Fri. However HREF
shows about a 20-40% chance for MVFR cigs to develop 12-17Z Thu,
but other guidance is not indicating lower flight conditions.

PDX AND APPROACHES...Expect VFR conditions through the TAF period.
Some model soundings indicate surfaced base inversion developing
leading to a shallow (below 1000 ft) cloud layer forming. But the
forecast soundings are biased too cold & moist and appear
overdone. Though wouldn`t be surprised to see a FEW-SCT layer
below 1000 ft form 12-16Z.
/mh
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.MARINE...
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Weak high pressure will continue building across the
northeast Pacific into Thursday, leading 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 this afternoon
and tonight (most likely outcome for central/southern waters is
gusts up to 25 kt). Most model guidance suggests winds will back
off a bit for Friday, but there is still a high probability (>75%
chance) wind gusts will peak above 20 kt across the waters off the
central coast of Oregon. As a result, a Small Craft Advisory
remains in effect for zones PZZ273, PZZ272, PZZ253, and PZZ252
Thursday into Friday morning.

There is increasing agreement a more organized and stronger storm
system will move into the northeast Pacific Sunday. This will
bring a high probability (80-90% 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 40-70%
chance for at least a brief period of unusually late season Gale
Force southerly wind gusts of 35 kt developing sometime late
Sunday into Sunday night. Probabilities of this happening are
highest off the far north Oregon and south Washington coasts than
areas farther south towards Lane County.
mh -TK/JH
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.PQR WATCHES/WARNINGS/ADVISORIES...

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OR...None.
WA...None.
PZ...Small Craft Advisory from 3 PM this afternoon to 5 AM PDT
     Friday for PZZ252-272.

     Small Craft Advisory from 11 AM this morning to 11 PM PDT
     Friday for PZZ253-273.
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$$

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