849
FXUS66 KPDT 180518
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1018 PM PDT Mon Aug 17 2026

.KEY MESSAGES...
- Low (<20%) shoer and thunderstorm chances this afternoon and
  evening across far eastern Oregon.

- Gusty west winds and low relative humidity will combine to
  create critical fire weather conditions Tuesday afternoon,
  mainly across the Columbia Basin of Oregon.

- Another chance of showers and thunderstorms and gusty winds
  toward the of the week, associated with an upper low.

&&

.DISCUSSION...
Southwesterly flow over the region today will give way to a more
split flow regime on Tuesday. There is still a low <20 percent)
possibility of showers and thunderstorms, mainly across Wallowa
County and the Blue Mountains as some short waves move through,
but chances are lower than the last few days.

The split flow that develops overnight into Tuesday will bring
gusty westerly winds. These winds could gust as high as 30 mph
across the Kittitas valley, Simcoe Highlands Columbia Basin,
Gorge and Foothills of the Blue Mountains. Across all of these
areas, except the Kittitas Valley, where RH values are expected
to be a bit higher, Red Flag Warnings have been issued for
Tuesday.

After Tuesday, the region is expected to remain in a dry west to
southwest flow through midweek as low pressure moves from
southwest to northeast off the Pacific Coast. As we approach
the weekend, the low is expected to weaken into an open trough
and move onshore in Washington/Oregon likely sometime on
Saturday.

There are still some differences in the models that have to be
resolved, but overall there is decent agreement. Winds will
likely increase beginning Friday and even more into Saturday and
continuing into Saturday night before decreasing. Winds could
gust in the 25 to 35 mph range, and possibly to 40 mph,
especially across the normally breezier areas of the Kittitas
Valley, Simcoe Highlands, Columbia Basin, Gorge and Foothills of
the Blue Mountains. At this point, NBM probabilities of wind
gusts >=25 mph are >80 percent in these locations while wind
gusts >=39 mph >40 percent.

Additionally, the exact position and timing of the trough will
determine precipitation threat, but there is at least some
threat of showers and thunderstorms later Friday into Friday
night and, potentially a better threat on Saturday.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
VFR conditions will persist through the forecast period.
Confidence remains low (15-25%) in vsby reducing to MVFR or
lower at sites due to smoke impacts except at RDM which is MVFR
and will stay as such through much of the period. Winds will be
below 12 kts across all sites except DLS which is at 10g15 and
all. Breezy winds will increase tomorrow afternoon at sites
DLS/PDT/RDM/ALW.

&&

.FIRE WEATHER...
There remains a low (<20 percent chance of showers and
thunderstorms across far eastern Oregon this afternoon and
evening.

The next threat is for gusty west winds developing on Tuesday,
mainly across the Oregon Columbia Basin and surrounding areas,
as humidity values remain low (around 15 percent). Fire weather
conditions will become critical in these areas and Red Flag
Warnings have been issued.

After Tuesday, the next time period of concern looks to be
closer to the weekend as an area of low pressure approaches the
Oregon and Washington coasts. Winds will increase and become
gusty especially on Saturday and there will be at least some
shower and thunderstorm potential, over the mountains. All of
the finer details will come into better focus over the next few
days.

&&

.Preliminary Point Temps/PoPs...
PDT  58  91  54  90 /   0   0   0   0
ALW  65  92  62  91 /   0   0   0   0
PSC  60  95  57  93 /   0   0   0   0
YKM  60  95  60  92 /   0   0   0   0
HRI  62  93  60  92 /   0   0   0   0
ELN  59  87  58  88 /   0   0   0   0
RDM  49  91  48  92 /   0   0   0   0
LGD  57  92  54  93 /  20   0   0   0
GCD  56  93  55  95 /  10   0   0   0
DLS  62  90  60  91 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
WA...None.
OR...Air Quality Alert until 1 PM PDT Wednesday for ORZ041-505-506-
     509>511.
     Red Flag Warning from noon to 10 PM PDT Tuesday for ORZ691-701-
     703.

&&

$$

DISCUSSION...77
AVIATION...90
FIRE WEATHER...77