190
FXUS66 KPDT 042340
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
440 PM PDT Tue Jun 4 2024

Updated Aviation Discussion

.AVIATION...00Z TAFs...VFR conditions expected over the next 24
hours. Winds remain breezy across the region, with gusts 20-25
possible through the evening and beginning of the night, but
should begin to drop to 10 knots or less around 06-12Z. Low level
wind shear possible at BDN/RDM for the next couple of hours, but
already seeing reports it is weakening to around +/- 10 knots, and
should continue to decline. Cloud decks remain generally at the
mid-level, between 5-10k feet, but should lift and clear through
the nighttime hours. All sites SKC tomorrow. Goatley/87


&&

.PREV DISCUSSION... /issued 247 PM PDT Tue Jun 4 2024/

SHORT TERM...Tonight through Thursday...Satellite imagery this
afternoon shows mostly cloudy skies across the forecast area, with
impressive gravity wave cloud streaks area wide. However, area
radar shows little returns across the forecast area, except for
light shower activity mostly confined to the central WA Cascades.

Currently, pressure gradients across eastern WA/OR have tightened
behind the cold front passage earlier today. With the shortwave
currently passing through WA, the pressure gradients will remain
tightened through the evening, resulting in a continuation of
breezy winds across the lower elevations and Simcoe Highlands.
While much of the lower elevations will have seen winds between
15-25mph with gusts to around 35mph, some exposed ridges and the
Hanford area have had stronger 850mb winds up to 45mph and
sustained winds of 25-30mph mix down this afternoon. The breezy
winds and shower activity will continue through this evening, but
will diminish overnight as the shortwave exits into western MT.

By tomorrow morning, an upper level ridge of high pressure in the
Desert Southwest will build into the PacNW and continue to build
over the western CONUS through the late week. This will result in
dry conditions and light winds across the forecast area Wednesday
and Thursday. Not only that, but temperatures will be on the
increase as well, with Thursday afternoon temperatures warming
into the mid to upper 80s in the lower elevations, and mid 60s to
70s in the mountains. While conditions are expected to remain dry
through the middle of the week, deterministic guidance, and even
their ensemble counterparts, have been showing a signal for
isolated thunderstorms to develop across southern and
southeastern OR by Thursday afternoon. While confidence is low
(15-20%), the increased surface instability across the southern
border of the forecast area and increased moisture in the mid
levels would certainly support the development of a few isolated
storms entering into southern Grant county Thursday. Lawhorn/82

LONG TERM...Friday through Tuesday...Models have come into better
agreement in the long term period with fewer significant
differences. The main focus of the long term will be a strong ridge
over the area with a heat wave Friday and Saturday and the chances
for afternoon and evening thunderstorms Friday through Sunday. The
Extreme Forecast Index highlights temperatures Friday and Saturday
with values of 0.85 to 0.90. Friday has the highest values mainly in
Oregon and especially over the mountains. Saturday the entire area
is highlighted with a Shift Of Tails over the Washington Columbia
Basin and eastern mountains of Oregon suggesting a more extreme
event is possible. Similar values, if not a little higher, are
present in the overnight lows Friday night through Sunday night.
Sunday drops down to 0.78 with the highest values in the Columbia
Basin. Values indicate warm but not unusual temperatures Monday
through Tuesday. Instability is also highlighted Friday through
Sunday. Friday highlights the Oregon Cascades and the Ochoco-John
Day Highlands and Southern Blue Mountains with a value of 0.83.
Saturday has the strongest highlight with a value of 0.96 and the
highest values are over the Cascades and the eastern mountains. This
day will have the best chance for thunderstorms. The value drops to
0.82 on Monday mainly over the eastern mountains.

For Friday, clusters show excellent agreement in having a strong
ridge centered over the Rockies with a southwest flow over our area.
Temperatures will rise about 5 degrees from Thursday with highs in
the upper 80s to mid 90s and in the mid 70s to mid 80s in the
mountains. This will be about 15 degrees above normal for early
June. Overnight temperatures in the Columbia Basin will be 60 to 65
which will provide little heat relief and this will create moderate
heat risk levels Friday and Saturday. The Columbia Basin will have a
70-90 percent chance of 90 degree temperatures and the Blue Mountain
Foothills and central Oregon will have a 35-50 percent chance of 90
degree temperatures. Only the Tri-Cities area reaches a 10 percent
chance of 100 degree temperatures. With moisture in a southwest flow
and increasing instability, have a slight chance of thunderstorms in
the late afternoon in the Ochoco Mountains and John Day Basin.

Saturday, model clusters show some minor differences in the strength
of the ridge and the axis location, but it remains similar to
Friday. Temperatures warm a couple of degrees in the Columbia Basin
and the eastern portions of the area though in central Oregon
temperatures cool a couple of degrees, presumably due to increasing
clouds and chances for showers and thunderstorms in the afternoon.
High temperatures will be in the lower to mid 90s in the Columbia
basin and in the 80s elsewhere. Chances of reaching 90 degrees are
above 90 percent in the Columbia Basin and Yakima Valley and around
60-70 percent in the Kittitas Valley, Blue Mountain Foothills and
Columbia Gorge. Chances are no more than 25 percent elsewhere.
Hermiston and the Tri-Cities have a 20-25 percent chance of reaching
100. Thunderstorms are expected to develop in the afternoon with a
slight chance to chance mainly over the eastern mountains.

On Sunday models bring some form of trough to the west coast and
shift the ridge eastward a couple of hundred miles. This will give
us a marine push through the Cascade gaps in the afternoon with
winds increasing to 10 to 20 mph. This will cool temperatures 5 to 8
degrees and limit a slight chance of showers and thunderstorms
mainly to the higher terrain of the eastern mountains. Highs will
drop to the mid 80s to lower 90s with mid 70s to lower 80s in the
mountains.

On Monday, model clusters mostly want to have a ridge over the area
though 10 percent of model members keep a weak trough over the area.
By Tuesday, all members have a broad trough centered over our area.
Have kept temperatures a degree or two warmer than Sunday with highs
in the mid 80s to lower 90s with mid 70s to mid 80s in the
mountains. Do not foresee any precipitation Monday and Tuesday.
Perry/83

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  50  77  49  83 /  10   0   0   0
ALW  51  79  51  86 /  10   0   0   0
PSC  53  81  52  88 /   0   0   0   0
YKM  44  78  47  86 /  10   0   0   0
HRI  51  81  50  88 /   0   0   0   0
ELN  43  74  47  83 /   0   0   0   0
RDM  47  80  47  84 /   0   0   0   0
LGD  49  77  49  83 /  10   0   0   0
GCD  48  83  51  89 /   0   0   0   0
DLS  51  81  52  87 /  10   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...Wind Advisory until 8 PM PDT this evening for WAZ521.

&&

$$

SHORT TERM...82
LONG TERM....83
AVIATION...87