304
FXUS66 KPDT 242223
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
323 PM PDT Mon Aug 24 2026

.KEY MESSAGES...
- Above-normal temperatures 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 this afternoon/evening, and for the
  northern Blue Mountains Tuesday afternoon/evening.

- Breezy westerly winds Wednesday, with locally medium-high
  probability (50-80%) of Red Flag conditions in the eastern
  Columbia River Gorge and western half of the lower Columbia
  Basin. Lower probability (<50%) of Red Flag conditions due to
  wind and low relative humidity elsewhere.

&&

.DISCUSSION...
Water vapor imagery shows an upper-level ridge of high pressure
building over the region. Meanwhile, a large, upper-level
closed low is churning off southeast Alaska, and a somewhat
smaller and weaker closed low is located to our west in the
eastern Pacific. A weak shortwave embedded within southwesterly
flow aloft is noted over the northwest Great Basin.

The aforementioned upper-level ridge is forecast to 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 to near
100 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 (10-50%) 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 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, with a weak shortwave embedded in southwest
flow aloft passing over northern California and southeast Oregon
this 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
with 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 (5-10%) chances of
convection again over the Blue Mountains. There is medium-high
confidence (50-80%) in localized overlap of breezy winds and
critically low relative humidity in the eastern Columbia River
Gorge and western half of the lower Columbia Basin, per NBM
probabilities. Elsewhere, there are lower probabilities (<50%)
of overlap of wind/rh thresholds.

Thursday through the remainder of the week, anticipating near-
to below-normal temperatures and diurnally breezy westerly
winds through the Cascade gaps as troughing moves onshore.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...VFR conditions to
prevail through the period. Low confidence (15-20%) in smoke
impacts at sites, but have included HZ FU at sites ALW/PDT due
to proximity to area wildfires. Winds will be light, 12kts or
less, through the period. Lawhorn/82

&&

.Preliminary Point Temps/PoPs...
PDT  55  94  59  93 /   0   0   0   0
ALW  62  95  66  94 /   0   0   0   0
PSC  57  96  61  96 /   0   0   0   0
YKM  61  95  63  95 /   0   0   0   0
HRI  58  95  63  94 /   0   0   0   0
ELN  57  93  61  92 /   0   0   0   0
RDM  50  94  50  91 /   0   0   0   0
LGD  56  98  58  97 /   0  20  20  10
GCD  57  96  58  96 /   0  10  10   0
DLS  65  95  65  89 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
WA...Air Quality Alert until noon PDT Wednesday for WAZ026-028>030-
     522-523.
OR...Air Quality Alert until noon PDT Wednesday for ORZ044-502-503-
     507.

&&

$$

DISCUSSION...86
AVIATION...82