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000
FXUS66 KPDT 290335
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
835 PM PDT Sun May 28 2023

.SHORT TERM UPDATE...The isolated showers and thunderstorms that
developed in our forecast area have dissipated, although there are
isolated activity south of Deschutes County. These are associated
with a closed low off the CA coast that sent a weak wave across
south central OR. Precipitation will remain south of our area. Winds
are also decreasing and locally breezy along the eastern valleys
of the Cascades. It will be a quiet weather night as skies clear
and winds will be light for most of the region. No updates planned
for forecast.

No major weather concerns are anticipated on Memorial Day. There
will be isolated showers and thunderstorms in our far southern
zones. These will be similar to the thunderstorm behavior
experienced today--weak and pulsating. The area with the best
chance of thunderstorms will be over far southern Wallowa County
where there is a southwest flow aloft and instability. Most of the
CAMS support this (NAM Nest had very little indication of showers
and thunderstorms). NBM also has 20% probability of thunderstorms
for areas east of John Day and La Grande on Monday. It will be
another breezy day through the Cascade gaps, including the
Kittitas Valley and the eastern CR Gorge with a westerly flow
aloft and tight cross Cascade gradient. It will be several degrees
warmer tomorrow with highs in the mid 70s to mid 80s...85 to 90 in
the Lower Columbia Basin. Wister/85


&&

.AVIATION...06Z TAFs...It will be mostly clear for the next 24
hours. FEW-SCT cumulus clouds with bases AOA 8K feet along with
thin high cirrus can be expected Sunday. Winds decrease tonight
but increase with similar magnitude on Memorial Day. Winds at DLS
will increase from the NW 15-20G30kts.  Other TAF sites will
be 5-15 kts with variable directions. Any showers and
thunderstorms tomorrow will be isolated over the higher terrain
and not expected to be in the vicinity of the terminal airports.
Wister/85


&&

.PREV DISCUSSION... /issued 450 PM PDT Sun May 28 2023/

LONG TERM...Wednesday through Sunday...Confidence in the
longwave pattern from Wednesday through Sunday is growing, but
details of the pattern remain fuzzy especially towards the weekend.
Temporally averaged across the period, the main feature over the
CONUS per ensemble guidance is a relatively stationary omega block
with meandering upper-level low pressure over the Southwest and
Southeast and an upper-level ridge over the Central US. Ensemble
guidance further suggests that two shortwaves will pass through the
southwest flow aloft over the Pacific Northwest on Wednesday and on
Thursday, but timing is still uncertain especially with the latter
feature. While southwesterly flow aloft typically signals
thunderstorms for the forecast area, moisture and instability are
not impressive so have seen a bit of a downward trend in PoPs and
thunderstorm chances. The main area to watch will be the eastern
mountains with the highest confidence in precipitation coming on
Wednesday and Sunday. Near-normal temperatures are forecast
Wednesday and Thursday, but confidence is increasing in a warming
trend for Friday through the weekend as troughing in the Gulf of
Alaska will most likely (70-80% chance) remain offshore with the
blocking pattern remaining dominant. The 12Z ECMWF EFI is starting
to signal ensemble agreement in climatologically unusual maximum and
minimum temperatures for some of the forecast area. Should the
solution favored by the majority (60-65%) of GEFS members pan out,
the closed low would sag closer to the coast for Saturday and Sunday
with showers and thunderstorms for the mountains.

As far as sensible weather concerns, the shower and thunderstorm
chances look best Wednesday and Sunday, though chances are non-zero
Thursday, Friday, and Saturday as well. Breezy to locally windy
conditions are forecast with the shortwave passage on Wednesday, and
locally breezy conditions look to remain in place Thursday and
Friday with surface winds switching to offshore for Saturday and
Sunday. Low afternoon RHs are forecast each day, though not
critically low, especially given that it is still spring. High
temperatures are forecast to climb to 5-15 degrees above normal
Friday through the weekend. Plunkett/86



&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  51  84  51  81 /   0   0   0   0
ALW  54  88  54  84 /   0   0   0   0
PSC  55  90  56  87 /   0   0   0   0
YKM  51  87  51  84 /   0   0   0   0
HRI  53  88  54  85 /   0   0   0   0
ELN  48  82  48  81 /   0   0   0   0
RDM  45  82  46  78 /   0   0   0   0
LGD  48  81  49  79 /  20  10  10  20
GCD  46  81  48  78 /  10  10  10  30
DLS  51  86  51  79 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
&&

$$

SHORT TERM...99/85
LONG TERM....86
AVIATION...85