297
FXUS66 KPDT 180006
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
506 PM PDT Fri May 17 2024

.AVIATION...00Z TAFs...VFR conditions are very likely (95-99%
chance) to continue through the period. After FEW-SCT stratocumulus
diminish this evening, FEW-SCT mid- and high-level clouds will
move over the forecast area overnight into Saturday morning.
Stratocumulus will redevelop Saturday afternoon across the
Columbia Basin and adjacent foothills and spread eastward to the
Blue Mountains through evening. Precipitation chances for TAF
sites will be low (0-20% chance), highest at KPDT/KALW late
Saturday afternoon and evening (10-20% chance) with less than a
10% chance elsewhere. Winds of 10-15 kts and gusts of 15-25 kts
this evening will slacken overnight then increase in magnitude
Saturday morning and afternoon. Plunkett/86

&&

.PREV DISCUSSION... /issued 209 PM PDT Fri May 17 2024/

SHORT TERM...Tonight through Sunday night...A strong west-
northwest flow aloft remains in the wake of an upper level
shortwave that swept across the region late last night. Strong
winds at the surface will continue in the lower elevations this
evening and gradually decrease overnight as boundary layer winds
decouple from winds aloft. The wind advisory for the Kittitas
Valley is set to expire at 2 PM. The wind gusts for the next
several hours will flirt around the advisory criteria near
Ellensburg and Ryegrass Summit, and the plan for is to extend the
advisory until 6 PM. From 6 PM until sunset, forecast will show
gusts 35-45 mph based on the majority of the high resolution
models. The tight cross Cascade gradient will remain through the
night and into Saturday morning, therefore the eastern CR Gorge
and some of the wind exposed gaps will remain breezy to windy
through the night.

The forecast area will be under a stationary trough through the
weekend. Another upper low initially over the BC coast will sag
south across WA on Saturday with enhanced vorticity that will
result in numerous showers along the northern half of the WA
Cascades and a 20-30% chance of light showers over the northern
Blue Mountains and foothills Saturday evening. The rest of the
area will be dry and breezy with gusts 25-35 mph in many areas.
NBM probabilities of gusts > 35 mph on Saturday is minimal or
zero with the exception of localized spots in the Kittitas Valley
and the eastern CR Gorge.

Sunday and Sunday night will be met with a cool northerly flow
aloft. After a chilly start to the morning, the afternoon will be
partly to mostly cloudy with a 20-30% of orographic mountain
showers and temperatures slightly below seasonal average. Snow
levels will be around 4000 feet, and some of the mountain passes
could see a light dusting of snow. Early morning temperatures are
not forecast to fall below freezing in the zones currently in the
growing season, but close with low in the mid-30s resulting in
areas of frost in the Grande Ronde Valley, Simcoe Highlands and
north central Oregon. Wister/85

LONG TERM...Monday 12Z (Monday) to Saturday 06Z (Friday
night)...Not much has changed this work week with the NW flow
aloft over PacNW left behind as the low over eastern Canada moves
farther east while this trough pattern persists. Precip chances
will be very low (<10%) at the low elevations however, chances of
light mountain showers will increase as the front passes over
PacNW (20-40%) starting Tuesday thus bringing orographic lift into
the moisture- starved trough. This can induce thunderstorms across
Wallowa County for Monday through Wednesday but with low chances
(<20%) due to weak instability and less moisture from the dry
airmass.

QPF amounts remain very light at the low elevations whereas
Cascades increase up to 0.25 inch Tuesday including the Blues
for Wednesday and Thursday before decreasing Friday. Gusty winds
continues at around 20-30kts Tuesday into Wednesday night mainly
along Simcoe Highlands, OR Columbia Basin, Kittitas and Yakima
Valley with strong surface pressure gradient due to the front
passing. The NBM probabilities of wind gusts >=22 mph shows high
chances greater than 70%, but 40-60% over Ochoco-John Day
Highlands.

Good agreement overall with the models and ensembles on trough
pattern with light mountain showers Thursday and Friday. Though,
23% of total cluster members favor the low over PacNW as does
the GFS model whereas other models show the low moving east from
the forecast area after Wednesday but no major differences in
shower chances. High temperatures will be in the 60-70s at the low
elevations with 50s-60s at the mountains. Snow levels will
increase to about 5000ft or higher this week. Feaster/97

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  39  67  39  63 /   0   0  10   0
ALW  44  70  44  66 /   0   0  20  10
PSC  46  72  45  71 /   0   0  10   0
YKM  39  69  38  69 /   0   0   0   0
HRI  44  71  43  70 /   0   0   0   0
ELN  41  63  40  63 /   0  10   0   0
RDM  35  66  33  58 /   0   0   0   0
LGD  36  66  38  58 /   0   0  10  10
GCD  36  68  36  59 /   0   0   0   0
DLS  44  67  45  66 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...Wind Advisory until 6 PM PDT this evening for WAZ026.

&&

$$

SHORT TERM...85
LONG TERM....97
AVIATION...86