671
FXUS66 KPQR 291743 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
1043 AM PDT Wed May 29 2024

Updated aviation discussion.

.SYNOPSIS..Showers continue to diminish today with warmer and drier
weather returning Thursday and Friday. A much wetter and slightly
cooler weather pattern returns over the weekend into early next week.

&&

.SHORT TERM...Today Through Friday...The postfrontal air mass
continues to to develop through today as a embedded upper level
shortwave trough continues to push eastward. This will result in
light showers this morning continuing to diminish through the
evening. CAMs are showing CAPE values of 100-200 J/kg areas north of
the Portland/Vancouver Metro area (15-20% probability) through this
evening. So, can`t rule out the possibility of some rumbles of
thunder. Tonight a ridge of high pressure starts to develop which
will start a warming and drying trend for Thursday and Friday.
Daytime highs today will be below normal with temperatures inland in
the mid to upper 60s, along the coast temperatures will be in the
upper 50s to mid 60s and temperatures in the Cascades will be in the
upper 40s to mid 50s. Winds will start as onshore today and slowly
become northerly by tonight and will continue to be northerly through
Friday. /42

.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. 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

&&

.AVIATION...As of 1730Z Wednesday, showers continued moving over
the region, primarily northward of a line extending from KTMK to
KSLE. Cigs were mainly VFR across the area aside from brief drops
to MVFR cigs with passing showers, affecting mainly KAST, KPDX,
and KTTD. Have handled this with TEMPO groups with a start/stop
time that reflects the most likely time frame for showers to move
through. This trend will continue through Wednesday afternoon
before showers diminish Wednesday evening, mainly after 00-03z
Thursday.

Northwesterly winds will increase to 10-15 kts around 21-23Z
Wednesday to 04-06Z Thursday for all terminals throughout the
region as the pressure gradients tightens. With possible clouds
breaks, could see a brief/isolated thunderstorm or two over or
near the Portland/Vancouver metro and points north until 21Z
Wednesday (15% chance).

PDX AND APPROACHES...Expect VFR conditions through the TAF period
aside from very brief drops to MVFR cigs with passing showers
through 21z Wednesday. There is a 15% chance for a brief/weak
thunderstorm to impact the terminal until 21z Wednesday. Any
intense shower or thunderstorm would almost certainly bring a
brief dip into MVFR thresholds during that period as well.
Otherwise, northwesterly winds will increase to 10-15 kt between
00Z-05Z Thursday. -TK/JH

&&

.MARINE...Weak high pressure builds across the northeast Pacific
this morning 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 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. Have issued a Small Craft Advisory
for zones PZZ273, PZZ272, PZZ253, and PZZ252 for Thursday into
Friday morning as a result.

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. -JH/Neuman

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory from 5 PM Thursday to 5 AM PDT Friday for
     PZZ252-253-272.

     Small Craft Advisory from 11 AM Thursday to 11 AM PDT Friday
     for PZZ273.
&&

$$

www.weather.gov/portland

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