304
FXUS66 KPDT 302302
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
405 PM PDT Thu May 30 2024

Updated Aviation Discussion

.SHORT TERM...Tonight through Saturday...The short term remains
quiet, with no sensible weather concerns anticipated through the
start of the weekend under a transient ridge that will give way to
a quick moving and weak shortwave, with some mountain showers and
our usual breezy but sub-advisory level winds possible at that
time.

Ensembles have a good agreement on the pattern over the next few
days as a ridge makes its way onshore and then quickly moves
eastwards as a weak shortwave trough sweeps across Saturday into
Sunday. Under this pattern, a steady warming trend will occur
thanks to the ridging, with temperatures steadily rising around 4
to 8 degrees tomorrow, with a smaller increase to possibly small
decrease on Saturday as the front associated with the shortwave
trough moves across the region. Meanwhile, conditions stay calm
and clear most of tonight through Friday, but by Saturday overcast
skies are expected with the passage of the boundary along with
breezy winds. Winds with the passage of the system look to be
fairly run of the mill for the region, strongest in the Kittitas
Valley, Simcoe Highlands, and along the Columbia Gorge through
lower Columbia Basin. The NBM projects a 45-90% chance of winds
gusting to or in excess of 40 mph in these respective areas, but
raising the threshold to 45 mph all but wipes out probabilities,
keeping these conditions well below wind advisory criteria.
Meanwhile, although some light showers in the mountains could be
possible as this system passes, the probability for greater than
or equal to a tenth of an inch of precipitation is zero everywhere
except the northern Cascades, which only have a 20% chance at
best. Overall, we remain generally quiet through the beginning of
the weekend, a precursor to a bit more active pattern moving into
next week. Goatley/87

.LONG TERM...Sunday through Thursday...Sensible weather concerns
through the extended period will revolve around the passage of an
upper trough and associated frontal system Sunday through Monday,
bringing with it widespread rain chances and windy conditions. By
Tuesday morning upper level ridging will build into the PacNW
from the desert Southwest, starting a drying and warming trend
that will extend through the late week.

Sunday starts with a transient ridge quickly traversing the
region ahead of an upper trough feature out in the northeast
Pacific. Following on the heels of the ridge exit Sunday
afternoon, a warm front associated with the upper trough will
arrive to the Cascades by the afternoon. Light rain showers will
push across eastern WA and OR Sunday evening with the warm front
passage, and will pick up in intensity Sunday night through
Monday morning with an associated cold front boundary passage.
Monday afternoon into the evening, shower activity will continue
across the eastern mountains and Cascades as the upper trough
quickly slides across the PacNW. Overall, the rainfall associated
with this system will be beneficial to the mountain and lower
elevation regions, though periods of moderate to locally heavy
rain can be expected with the cold front passage. Ensemble
guidance points to an Atmospheric River as the culprit to the
increased rainfall Monday morning. ECMWF and GFS ensemble mean
solutions show a 150-200% of normal PWATS with the cold front
passage, and GFS ensemble AR landfall tools show a 90-100% chance
of IVT greater than 250 kg/m/s across southeast WA and northeast
OR Monday morning. As for rainfall amounts through 5PM Monday:
along the Cascade crest, northern Blues, and Wallowas NBM
probabilities for 0.75 inches of rainfall is 55-75%; across the
Cascade east slopes, Blue mountain foothills, and southern Blues
NBM probabilities for 0.5 inches of rainfall are 45-60%; and
across the remainder of the forecast area there is 45-60% chance
for 0.25 inches of rainfall. Ensemble and deterministic guidance
also indicate the cold front passage initiating isolated
thunderstorms across the eastern mountains Monday
afternoon(confidence 30-40%).

Besides precipitation, the cold front passage and the follow-up
from the upper trough will tighten pressure gradients across the
region, resulting in windy conditions through the Cascade gaps and
across the Columbia Basin. Most recent NBM QMD probabilities show
a 70-80% chance of wind gusts greater than 45mph in the OR
Columbia Basin, Simcoe Highlands, the Gorge west of the Dalles,
and the eastern portions of the Kittitas valley. As for the rest
of the lower elevations, NBM probabilities for gusts greater than
40 mph are between 55-70%.

Tuesday through Thursday, 70-80% of ensemble members from the GFS,
ECMWF, and Canadian ensemble suites are in agreement of an upper
level ridge building into the PacNW from the desert southwest.
While drying conditions are expected with ridging patterns, there
are chances (25-45%) of rain showers across the WA Cascades
Tuesday as weak shortwave impulses clip this area. Lastly,
temperatures will be on a 5 to 9 degree increase each day, with a
65-80% chance that the lower elevations will exceed 80 degrees by
Wednesday, and a 45-60% chance to exceed 90 degrees Thursday in
the Lower Columbia Basin, eastern Gorge, and the Yakima valley.
Lawhorn/82


&&

.AVIATION...00Z TAFs...Clear skies and light terrain-driven winds
will continue for the next 24 hours. There is a chance (40%) of
gusts to 15 kt from the north this evening at RDM and BDN.


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  41  75  50  76 /   0   0   0   0
ALW  45  77  52  79 /   0   0   0   0
PSC  47  79  54  83 /   0   0   0   0
YKM  40  78  52  79 /   0   0   0   0
HRI  44  79  52  81 /   0   0   0   0
ELN  41  76  52  73 /   0   0   0   0
RDM  37  77  45  73 /   0   0   0   0
LGD  38  72  47  72 /   0   0   0   0
GCD  38  76  47  75 /   0   0   0  10
DLS  47  81  56  76 /   0   0   0   0

&&

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

$$

SHORT TERM...87
LONG TERM....82
AVIATION...85