076
FXUS66 KPQR 300441 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
941 PM PDT Wed May 29 2024

Updated aviation discussion...

.SYNOPSIS...Diminishing showers this evening gives way to dry
weather and a slight warming trend to near 80 degrees through
Friday. A weakening front pushes across the area on Saturday,
pushing temperatures back down to the lower 70s, generally remaining
dry. Then, a much wetter system associated with tropical moisture is
expected Sunday through Monday.

&&

.SHORT TERM...Tonight through Friday night...The axis of an upper
shortwave trough has shifted east of the Cascades this afternoon,
with light rain showers gradually decreasing through early this
evening. Then, high pressure gradually builds across the region
bringing dry weather and northerly flow to the area. A transient
upper ridge moves across the Pacific NW on Friday. Expect this to
bring a warming trend through the end of the work week, with inland
temperatures warming to around 70 on Thursday and upper 70s to near
80 degrees on Friday. Onshore north-northwesterly flow will keep
temperatures at the coast near normal for late May. /DH

.LONG TERM...Saturday through Wednesday...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, but still in the lower 70s. 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, with the general trend toward a mostly dry day on Saturday.

Uncertainty in the overall pattern begins to grow on Sunday as the
remnants of Typhoon Ewiniar are ingested into the westerlies
crossing the Pacific. 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.

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 65-75% chance for
above average temperatures between June 6-12th. 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/DH

&&

.AVIATION...Showers have diminished across the region, and
satellite imagery as of 0430z Thu shows low clouds developing on the
west slopes of the Coast Range and Cascades. These low clouds could
push into the Portland Metro Area tonight. Guidance suggests a 30-
50% chance of IFR cigs between 11-16z Thu over the Portland Metro
and as far south as KUAO. Otherwise, expect predominately VFR
conditions through the morning with scattered to broken cloud cover
and north/northwest winds generally under 10 kt.

Upper level high pressure will build Thursday, leading to clearing
skies across northwest Oregon and southwest Washington. Surface
pressure gradients will also tighten after late morning Thursday,
which will lead to strengthening north/northwest winds. Winds could
gust up to 25 kt along the coast and southern Willamette Valley
Thursday afternoon.

PDX AND APPROACHES...30-50% chance of IFR cigs between 12-16z Thu.
Due to the low confidence, an IFR ceiling was not included in the
TAFs. Otherwise, expect predominately VFR conditions through the TAF
period with clearing skies throughout the day Thursday.
Winds will generally be from the northwest at 5-10 kt, and strongest
in the afternoon.      -Alviz

&&

.MARINE...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 by Thursday afternoon and
evening (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 over the weekend. This
will bring a high probability (>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. -TK/JH

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

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

     Small Craft Advisory from 11 AM Thursday to 11 AM PDT Friday
     for PZZ253-273.
&&

$$

www.weather.gov/portland

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