121
FXUS66 KPDT 222358 AAA
AFDPDT

Area Forecast Discussion...UPDATED AVIATION.
National Weather Service Pendleton OR
458 PM PDT Sat Jun 22 2024

.SHORT TERM...Tonight through Monday...An inverted thermal trough
continues to extend across the Great Basin and into eastern OR/WA
this afternoon, resulting in temperatures warming into the lower
90s so far this afternoon. Meanwhile, mid to upper level moisture
ahead of an approaching trough is moving across WA, resulting in
scattered cloud decks developing mainly across the northern half
of WA. These cloud decks have limited some heating across portions
of the WA Columbia Basin and adjacent valleys, but the
expectation is for these areas to continue to warm into the mid to
upper 90s over the next several hours.

Later this evening, an upper trough and surface cold front will
approach the PacNW, resulting in a marine push across the western
half of the region up to the Cascade crest. With the thermal
trough on the east side and a marine airmass developing on the
west side, pressure gradients will tighten across the Cascades,
resulting in breezy winds through the gaps and eastern Columbia
River Gorge. As the upper trough travels along the US/Canadian
border tomorrow, the marine airmass will deepen, and the
subsequent marine push through the Cascade gaps will result in
breezy to windy conditions in the Columbia River Gorge and the
Kittitas valley. In fact, sustained winds of 30mph and gusts up to
50mph will develop through the Kittitas valley, which has
warranted the issuance of a wind advisory (confidence 80-85%).
The winds associated with the marine push and cold front passage
tomorrow will spread into the Columbia Basin and the remainder of
the lower elevation locations across the forecast area, with winds
generally between 15-25mph and gusts up to 40mph (confidence
70-85%).

While the marine push will result in cooler temperatures and
relatively higher RHs through the Cascade gaps tomorrow, water
vapor imagery shows a very dry airmass at the bottom of the
trough. Model guidance depicts this very dry airmass at 700mb
mixing down along the cold front passage in the Columbia Basin
and adjacent foothill areas tomorrow(confidence 85%). With the
anticipated dry conditions and breezy winds, Red Flag Warnings
were issued for the Lower Columbia Basin for Sunday afternoon
through the evening. Though the system will be fairly dry, there
are chances (20-35%) of light rain showers developing along the
Cascade crest as early as tonight through tomorrow evening.
Otherwise, the thermal trough over the area will breakdown,
bringing temperatures back into the upper 70s to 80s across the
lower elevations.

Monday, pressure gradients will relax as westerly flow aloft
evolves into a broad, shallow ridge over the PacNW. That said,
locally breezy winds will develop in the afternoon through the
Gorge and the Kittitas valley. Temperatures will continue to be in
the upper 70s to 80s Monday afternoon, with otherwise quiet
conditions across the forecast area. Lawhorn/82

.LONG TERM...Monday night through Saturday. The ridge axis will move
across the region early on this extended period. A trough then
arrives to the PacNW Wednesday through late Thursday, bringing
increased winds and cool temperatures across the forecast area.
Mountain showers are also possible at the crest of the WA/OR
Cascades but, confidence remains low due to limited moisture
associated with trough and cold front (<30%). Temperatures will cool
late Wednesday through Thursday with the arrival of the trough but
an arrival of the ridge Friday through Saturday will bring warm
temperatures across the forecast area.

High chances (>70%) for wind gusts occurring late Wednesday
afternoon at 25-35 mph through early night along the lower Columbia
Basin, Columbia River and Kittitas Valley. Confidence remains high
for increased wind gusts in these areas Thursday as the trough
passes. Friday onward, locally breezy conditions will continue
across the forecast area with wind gusts at around 20 mph or less
(40-50% probability). Feaster/97

&&

.AVIATION...00Z TAFS...Limited aviation concerns with the main
forecast challenges revolving around winds and a cold front that
will advance across the area overnight. VFR conditions currently
area-wide with few-sct cu seen across portions of the eastern
mountains and limited mid-high clouds across portions of south
central WA. These latter clouds will push off east with clear skies
taking hold overnight.

A tight gradient cross-Cascade pressure gradient will sharpen early
tomorrow in tandem with a moderate belt of upper-level winds that
will be spreading across the area tonight and remain in place
through tomorrow. While light breezes will persist at most TAF sites
overnight, winds will start ramping up area-wide late morning
tomorrow. The exception will be KDLS overnight where there winds
will continue to be elevated (gusts around 20-25 kts at times). High
confidence (> 80%) in all TAF sites seeing frequent gusts in the 25-
30 kt range tomorrow outside central OR. Of which, strongest gusts
anticipated at the KDLS terminal with ~35 kts expected to be common.
Timing for uptick in gusts around 17-20 UTC, latest in central OR.
Most likely 24-hr daily peak gusts are expected to be strongest at
the KDLS, KPDT, and KPSC terminals with magnitudes in the 35-40 kts
range (highest at KDLS).

&&

.FIRE WEATHER...A Red Flag Warning is in effect from 1 PM to 8 PM
PDT Sunday for wind and low relative humidity for fire weather
zones OR641 and WA691. A marine push and cold front passage will
result in winds of 15 to 25 mph tomorrow in the lower elevations.
A dry airmass aloft will mix down the cold front boundary in the
Lower Columbia Basin, resulting in critically low relative
humidities coinciding with the elevated winds in this area.
Current confidence is high (80-85%) in critical fire weather
conditions being met tomorrow afternoon and early evening.
Elevated fire weather conditions will also be a concern through
the Cascade gaps, including the eastern Columbia River Gorge and
the Kittitas valley, where the strongest winds are expected. Lawhorn/82


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  59  81  48  81 /   0   0   0   0
ALW  62  85  52  84 /   0   0   0   0
PSC  63  87  53  85 /   0   0   0   0
YKM  56  82  48  82 /   0   0   0   0
HRI  63  85  53  86 /   0   0   0   0
ELN  55  71  48  78 /   0   0   0   0
RDM  51  82  43  82 /   0   0   0   0
LGD  56  84  48  81 /   0   0   0   0
GCD  55  89  48  86 /   0   0   0   0
DLS  61  77  53  83 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning from 1 PM to 8 PM PDT Sunday for ORZ641.

WA...Red Flag Warning from 1 PM to 8 PM PDT Sunday for WAZ691.

     Wind Advisory from 5 AM Sunday to midnight PDT Sunday night for
     WAZ026.

&&

$$

SHORT TERM...82
LONG TERM....97
AVIATION...80
FIRE WEATHER...82