265
FXUS66 KPDT 240506
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1006 PM PDT Sun Aug 23 2026

.KEY MESSAGES...
- Above-normal temperatures Monday through Wednesday as an
  upper-level ridge of high pressure builds overhead then shifts
  east to the northern Rockies.

- Very low chance (5-15%) of showers and thunderstorms for the
  southern Blue Mountains on Monday, and for the northern Blue
  Mountains on Tuesday.

- Breezy westerly winds Wednesday, with low-medium probability
  (20-60%) of Red Flag conditions in the Columbia Basin and
  Cascade gaps.

&&

.DISCUSSION...
Water vapor imagery shows an upper-level low exiting the region
to the east over southern Canada and the northern Rockies.
Meanwhile, a large, upper-level closed low is churning in the
Gulf of Alaska, and a somewhat smaller and weaker closed low
is located to our west in the eastern Pacific.

At the surface, widespread breezy conditions are present
beneath dry zonal flow in the wake of the low, with the most
notable winds through the Cascade gaps, Columbia Basin, and
Blue Mountain foothills. Temperatures are seasonably cool, a few
degrees below normal.

An upper-level ridge of high pressure is forecast to build
overhead tonight into Monday and gradually shift east over the
northern Rockies through Wednesday. This will result in warming,
mostly dry conditions areawide. Above-normal temperatures are
anticipated to peak in the 90s for most areas on Tuesday, with
portions of northeast Oregon seeing similar temperatures on
Wednesday. Accompanying HeatRisk looks to peak Tuesday/Wednesday
with medium-high (50-100%) probability of Moderate (level 2 of
4) HeatRisk for the majority of our population centers. A few
areas of the Columbia Basin have low-medium (10-45%) chances of
Major (level 3 of 4) HeatRisk. Moderate HeatRisk affects those
who are sensitive to heat, especially those without
cooling/hydration, while Major HeatRisk affects anyone without
cooling/hydration.

While mostly dry conditions are forecast Monday through
Wednesday, would be remiss for not mentioning the low
probabilities (5-15%) of convection each day. Ensemble NWP
guidance is in excellent agreement that the aforementioned lows
will slowly approach the Pacific Northwest by later Monday, with
a weak shortwave embedded in southwest flow aloft passing over
northern California and southeast Oregon late afternoon and
evening. This will present a low (5-15%) chance of high-based
showers and thunderstorms for the far southern Blue Mountains.
Any showers and thunderstorms that develop will be capable of
producing strong, gusty outflow winds.

Tuesday, guidance merges the two offshore lows, and wraps a
weak shortwave (the remnants of the smaller low) up the Pacific
coast. While the wave is not forecast to move inland across our
forecast area, weak synoptic-scale forcing coupled modest
diurnally induced instability, negative mid-level theta-e lapse
rates, and very marginal mid-level moisture indicate some
potential for afternoon convection. Best chances (5-15%) are for
the northern Blue Mountains, and the rest of far northeast
Oregon.

By Wednesday, guidance shows yet another shortwave swinging
around the parent offshore low, with low (5-15%) chances of
convection again over the Blue Mountains. There is higher
confidence (20-60%) in overlap of breezy winds and critically
low relative humidity in the Columbia Basin and Cascade gaps
Wednesday, per NBM probabilities.

Thursday through the remainder of the week, anticipating near-
normal temperatures and diurnally breezy westerly winds through
the Cascade gaps.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
VFR conditions prevail through the TAF period. Brief periods of
smoke making its way down to the surface in the overnight hours
bringing MVFR conditions is possible across sites in the
Columbia Basin and Foothills of the Blues (5 to 15 percent
chance). Otherwise winds are generally light and variable.

&&

.Preliminary Point Temps/PoPs...
PDT  49  91  54  93 /   0   0   0   0
ALW  55  93  61  95 /   0   0   0   0
PSC  53  93  56  95 /   0   0   0   0
YKM  57  90  61  95 /   0   0   0   0
HRI  53  92  57  95 /   0   0   0   0
ELN  51  86  57  92 /   0   0   0   0
RDM  45  91  50  94 /   0   0   0   0
LGD  49  93  55  97 /   0   0   0  10
GCD  52  95  56  95 /   0   0   0   0
DLS  59  93  64  96 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
WA...Air Quality Alert until noon PDT Monday for WAZ026-522-523.
OR...Air Quality Alert until noon PDT Monday for ORZ041-044-049-050-
     502-503-505>507-509>511.

&&

$$

DISCUSSION...86
AVIATION...95