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000
FXUS66 KPDT 020420
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
920 PM PDT Thu Jun 1 2023

.EVENING UPDATE...A few showers and storms approached Grant County
this afternoon/evening but with limited instability the activity
fell apart just as it reached the border. Some ongoing light rain
possible through the next couple of hours but should begin to
fully dissipate after that. Outside of this, forecast including
temperatures and winds have lined up well with observations, and
minimal edits were needed from the daytime package. Goatley/87

&&

.AVIATION...06Z TAFs...VFR conditions continue over the next 24
hours. Winds will be breezy tomorrow afternoon at DLS/RDM/BDN but
should remain at or below 20 kts, with diurnally driven winds
other sites. Skies clear except for FEW to BKN 25k ft at times.
Goatley/87


&&

PREV DISCUSSION... /issued 203 PM PDT Thu Jun 1 2023/

SHORT TERM...Today through Saturday...The axis of a weak shortwave
will move over the forecast area through Friday morning, leading to
a weak SW flow pattern overhead. Much of the moisture associated
with this system should fall to our south, however hi-res models do
show some weak convective showers forming across the southern
boundary of the CWA this afternoon into the early evening hours.
However, with CAPE as low as it is, current thinking is that any
activity that does spawn will primarily be orographic in nature and
be short in lifespan. This shortwave looks to potentially cut off
and linger about the interior NW heading into Friday, making for
some slight chance PoPs across our far eastern mountain zones, but
again much of the moisture looks to fall outside of our forecast
area.

Otherwise, a benign weather pattern will materialize over the
weekend as the interior NW finds itself saddled between a lifting
offshore low near BC and a building ridge over the central CONUS.
Such a pattern will keep us dry with temperatures rising well into
the 80s and even 90s beyond the short term period. These warming
conditions may lead to breezy gap flows across the usual suspect
areas (eastern Gorge, Kittitas Valley), but elsewhere expect quiet
and clear weather through the period. Evans/74

LONG TERM...Sunday through Thursday...The forecast area will be
under a southwest flow aloft between a strong upper trough off the
coast of Canada and an upper low (though a weak one) over the
Great Basin on Sunday. This leaves the forecast area in a dry and
stable pattern, except for some instability over extreme eastern
and southwest portions of the CWA. These areas of instability may
be conducive to isolated showers and thunderstorms, especially
over the eastern half of Wallowa County. Elsewhere it will be warm
and dry, with a warming trend in progress. High temperatures in
the lower elevations will be in the mid 80s to mid 90s, with the
warmest temperatures around the Tri-Cities and the Hanford areas
of WA. In the mountains, highs will be mainly in the upper 60s to
upper 70s, except possibly in the 80s in the mountainous valleys,
such as the Grande Ronde Valley and the John Day Basin. Cluster
analysis between the ECMWF, GFS and Canadian models are in very
good agreement on Sunday. Forecast confidence levels for sunday
are high (80-90 percent).

The southern upper low over the great basin will drift a bit
northward and westward and move closer to the forecast area on
Monday. This will cause an increase in the coverage and strength
of the instability over the southern and eastern most portions of
the CWA. However, deep moisture will be rather limited, and
therefore the showers and thunderstorms will still be isolated,
and again mainly just over extreme eastern and southern portions
of the CWA. Temperatures will continue to be on a warming trend,
with highs a couple degrees warmer than Sunday. Highs on Monday
will be in the mid to upper 80s to the mid to upper 90s in the
lower elevations, which are just a couple degrees warmer than
Sunday. Cluster analysis are still in very good agreement on
Monday, with still high forecast confidence levels (80-90
percent).

On Tuesday, the forecast area will be in between a weakening
upper trough to the north over northwest WA and British Columbia,
Canada. There will be an increase in moisture from the southern
upper low, which will be deepening over central CA. As this
moisture and instability penetrates further into the CWA, there
will be a greater coverage of showers and a slight chance of
afternoon/evening thunderstorms. These areas will now include
central OR northeastward across the Blue Mountains into extreme
southeast WA. Probabilities of precipitation will also be higher,
resulting in a better chance for showers and thunderstorms in
these areas. The warming trend will still be increasing
temperatures, with highs in the lower elevations on Tuesday in the
upper 80s to the upper 90s, which is just a couple degrees warmer
from Monday. In the mountains, highs will be in the 70s to lower
80s, except for mid to upper 80s in valleys such the Grande Ronde
Valley and the John Day Basin. Cluster analysis is not available
for Tuesday, however, the deterministic and ensemble models are
still in good agreement, with just a little bit more discrepancy.
Forecast confidence levels for Tuesday are moderate to high (60-80
percent).

The southern upper low pressure system will continue to drift
northward on Wednesday, with a greater coverage and probability of
showers and thunderstorms over the CWA. A slight chance of
showers will cover a larger area that extends further into the
Lower Columbia Basin and also along the Cascades. Thunderstorms
will now include the Blue Mountain Foothills southwest into
central OR. The warming trend will continue, with highs a couple
more degrees warmer than Tuesday, in the lower to upper 90s,
(possibly up to 100 in the Tri-Cities and Hanford areas). In the
mountains, temperatures will be in the mid 70s to mid 80s. These
temperatures will be about 15-20 degrees above normal for early
June, and this will also be the hottest day in the extended
forecast period. Cluster analysis are still in pretty good
agreement for Wednesday, however, there are greater differences
between the deterministic models. This lowers forecast confidence
levels to moderate, also because it is further out into the future
(50-70 percent).

On Thursday, the moisture with the upper low from the south will
continue to drift further northward, and this time will have an
impact on the entire forecast area. However, thunderstorm coverage
will be decreased. There will be a slight chance to a chance of
just showers that will cover the entire forecast area, mainly in
the afternoon and evening. The area of instability is expected to
only reach as far north as central OR northeast across the Blue
Mountain Foothills eastward and southward. Temperatures will be a
few degrees cooler, with mid 80s to mid 90s in the lower
elevations, and mostly in the 70s to lower 80s in the mountains.
Again, it will be warmer in the mountainous valleys, such as the
Grande Ronde Valley and the John Day Basin. Unfortunately, cluster
analysis are again not available for Thursday. However, there is
considerably more disagreement between the deterministic models,
even though the ensembles are still in fairly good agreement for
Thursday. Due to the greater differences, forecast confidence
levels for Thursday drops to low to moderate (30-50 percent).

As for winds, most areas will have predominantly light winds
through the extended forecast period, but there will be times
(mainly in the afternoons and evenings) when it will be locally
breezy. This will be especially true through the Cascade gaps,
the eastern Columbia Gorge, and in central OR. There really are
not any expected strong weather systems, cold fronts or tight
pressure gradients that will cause strong winds through the
extended period. 88

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  46  78  47  82 /   0   0   0   0
ALW  51  82  52  87 /   0   0   0   0
PSC  52  85  55  89 /   0   0   0   0
YKM  50  83  52  86 /   0   0   0   0
HRI  50  83  52  87 /   0   0   0   0
ELN  47  80  50  82 /   0   0   0   0
RDM  41  75  43  80 /   0   0   0   0
LGD  46  75  46  79 /   0   0   0   0
GCD  44  76  43  80 /  20   0   0   0
DLS  50  80  50  85 /   0   0   0   0

&&

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

$$

EVENING UPDATE...87
SHORT TERM...74
LONG TERM....88
AVIATION...87