375
FXUS66 KPDT 312333
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
433 PM PDT Fri May 31 2024

Updated Aviation Discussion

.AVIATION...00Z TAFs...VFR conditions expected over the next 24
hours. Light winds, generally 10 knots or less, through the
nighttime hours, becoming breezy and northwesterly to westerly
tomorrow with gusts 15-25 knots. High clouds tonight but cloud
decks lower tomorrow and increase in coverage, generally around
10-15k feet. Goatley/87


&&

.PREV DISCUSSION... /issued 218 PM PDT Fri May 31 2024/

SHORT TERM...Tonight through Sunday...Satellite imagery today
showing very little going on except for some thin cirrus spreading
east across the forecast area. Winds have generally be light and
terrain driven today, with many lower elevation locations already
warming into the low to mid 70s.

These quiet and dry conditions will persist through early tomorrow
morning as a transient upper ridge continue to influence the
region. By tomorrow morning, the ridge will have pushed east,
allowing a weak/dry shortwave trough to slide across the PacNW.
Scattered showers will develop by tomorrow morning across the WA
Cascades, spreading to the OR Cascade crest and the Wallowa
mountains in the afternoon. Cross Cascade pressure gradients will
tighten with the shortwave passage, resulting in breezy west winds
generally 15-20 mph in the lower elevations, with locally windy
conditions between 20-30 mph and gusts up to 40 mph developing
through the Cascade gaps and across the Simcoe Highlands, Kittitas
valley, and the OR Columbia Basin. Winds and shower activity will
decrease Saturday night as the shortwave exits into ID and a brief
westerly flow develops aloft.

The break from precipitation will be brief Sunday morning as a
parent low in the Gulf of Alaska swings an upper trough towards
the PacNW. A warm front will arrive ahead of the trough late
Sunday morning, with a stratiform rain spreading east across the
forecast area through the evening hours. Stratiform rain will turn
to showers overnight Sunday into Monday morning as a cold front
follows behind the warm front exit. Ensemble and deterministic
guidance are in great agreement in an Atmospheric River
accompanying the cold front passage overnight Sunday into Monday.
While the lower elevations will see some impact from the AR, the
mountains, especially those susceptible to upslope enhancement in
westerly flows, will see moderate to heavy rainfall through
Monday. By the end of Sunday night, most lower elevation
locations, Ochoco-John Day Highlands, and the southern Blue
Mountain foothills will see 0.05-0.1 inches of rainfall; the
northern Blue mountain foothills, Grande Ronde/Wallowa valleys,
and lower slopes of the Cascades will see 0.15-0.3 inches; the
northern Blues and Wallowas will see 0.3 to 0.6 inches; and lastly
the Cascade crest and upper slopes will see between 0.6-1.0 inches
with the higher amounts near/at the crest. As for winds, the warm
front passage will result in locally breezy winds from the south
southwest through the evening. Lawhorn/82

LONG TERM...Monday through Friday...An upper level trough will be
pushing inland on Monday. The initial wetting rains of the system
moving into the forecast area will give way to increasing westerly
winds becoming windy by afternoon. Precipitation will turn to
showers lingering mainly over the eastern mountains with a slight
chance of thunderstorms. A westerly flow remains over the region on
Tuesday continuing a chance of showers along the Cascade crest and
over the eastern mountains while still maintaining breezy westerly
winds.

Wednesday through Friday will see the building of an upper level
ridge over the western USA. There are some placement issues of the
ridge position in the models that still need to be considered but
overall this period will be dominated by warming temperatures. High
temperatures will reach 10 to 15 degrees above normal by Friday.
Other concern will be the increasing chance of convection over the
Thursday through Friday period mainly over central and eastern
Oregon. For now have just placed a slight chance of showers in the
Thursday through Friday forecast because of the model differences in
the placement of the ridge.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  49  76  51  71 /   0  10   0  30
ALW  53  79  54  74 /   0  10   0  30
PSC  55  81  56  74 /   0  10   0  30
YKM  53  77  49  69 /   0  10   0  40
HRI  52  80  55  74 /   0  10   0  20
ELN  52  71  48  66 /   0  10   0  40
RDM  47  72  46  69 /   0  10   0  20
LGD  45  72  47  71 /   0  10   0  20
GCD  47  75  46  73 /   0  10   0  10
DLS  56  76  55  69 /   0   0   0  50

&&

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

$$

SHORT TERM...82
LONG TERM....91
AVIATION...87