749
FXUS66 KPDT 180532
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1032 PM PDT Fri Jul 17 2026


.Updated Aviation Discussion.


.KEY MESSAGES...
- Red Flag Warning in effect for the Lower Columbia Basin of
  Oregon (OR690) until 10PM PDT Saturday due to breezy winds
  and low relative humidity.

- Diurnally breezy westerly winds through the Cascade gaps each
  afternoon and evening through Saturday.

- Hot, dry conditions early next week with increasing HeatRisk.

- Likely (>60% chance) increase in monsoonal moisture by mid-week.

&&

.DISCUSSION...
Water vapor imagery shows a closed mid/upper-level low churning
in the vicinity of Vancouver Island. This low will continue to
track northeast into British Columbia through Saturday, with
flow aloft turning from south-southwesterly to west-
southwesterly. Monsoonal moisture has largely been pushed to the
east of the forecast area, with the only area of lingering
higher PWATs (0.7-1.2" per RAP-based mesoanalysis) draped across
the northeastern Blue Mountains from the Elkhorns east through
Wallowa County. There is a very low chance (5-15%) of showers
and thunderstorms across the aforementioned area this afternoon
and evening, with dry conditions expected (95% confidence)
elsewhere. As of 2PM PDT, only modest CU development has been
observed over the Elkhorns, Wallowas, and surrounding sub-
ranges of the Blues.

At the surface, diurnally breezy winds are forecast from the
Cascade gaps eastward into the lower Columbia Basin this
afternoon and evening due to a cross-Cascade temperature and
pressure gradient and onshore flow. Neither gradient is nearly
as strong as yesterday`s, so not anticipating winds to be
anywhere close to advisory thresholds, but the combination of
locally breezy westerly winds (10-20 mph with gusts of 20-30
mph), low relative humidity (15-25%), and ongoing large
wildfires has prompted the issuance of a Red Flag Warning (RFW)
for fire weather zone OR691 (Lower Columbia Basin of Oregon)
through 10PM Saturday. Winds through the gaps should be a bit
stronger on Saturday as winds aloft turn more zonal, and there
is medium confidence (30-50%) in hitting critical thresholds of
wind/RH for the Kittitas Valley (WA690) and portions of the
lower Columbia Basin of Washington (WA691) on Saturday. Did not
issue any watches to avoid confusion with the ongoing RFW.

Winds will become lighter on Sunday as a 500-hPa ridge builds
into the Pacific Northwest. By Monday, lighter northerly to
easterly winds are forecast.

Tuesday through the remainder of the week, ensemble NWP
guidance shows the remnants of Tropical Storm Elida tracking
northward along roughly 120W and either replacing or getting
absorbed by an existing area of low pressure off the Pacific
coast. The evolution this low, its interaction with the broad
500-hPa ridge over the Western CONUS, and advection of monsoonal
moisture into the region will modulate precipitation chances
and temperatures across the forecast area. In general, there are
increasing precipitation chances across the region, especially
the Blue Mountains, Tuesday through Thursday, with a slight drop
on Friday. Chances peak at 25-40% on Thursday for the Blue
Mountains, with lower (10-25%) chances elsewhere.

On the topic of heat, chances of Major (level 3 of 4) HeatRisk
increase to 10-40% for the Blue Mountain foothills Tuesday
through Friday, with higher chances (20-70%) for the lower
Columbia Basin and surrounding valleys. This level of heat
affects anyone without cooling/hydration as well as heath
systems and industries.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
VFR conditions currently across all sites, which is expected to
stay the course. However, smoke from nearby wildfires may drop
visibilities to MVFR levels overnight for KPDT/KALW/KRDM/KBDN.
Breezy winds will pick back up by tomorrow afternoon for
KDLS/KPDT/KRDM/KBDN as gusts of 15-25kts will return.
Elsewhere, winds should stay at or below 10kts. 75

&&

.FIRE WEATHER...
Breezy diurnally driven westerly wind and low relative humidity
is expected through the Cascade gaps each afternoon and evening
through Saturday, leading to elevated to critical fire weather
conditions. A Red Flag Warning has been issued for OR691, the
Lower Columbia Basin of Oregon, from 2PM this afternoon through
10PM Saturday. Critical RH is not forecast overnight, but the
warning was issued for a two-day event to simplify messaging.
Confidence was a bit too low (30-50%) in overlap of critical
wind/RH for WA690 (Kittitas Valley), and WA691 (Lower Columbia
Basin of Washington) on Saturday to issue any headlines this
morning.

There is a very low chance (5-15 percent) of showers and
thunderstorms across the northeast Blue Mountains today.

Very warm to hot, and dry conditions are then forecast early
next week, followed by a slight chance (15-24 percent) to
chance (25-40 percent) of showers and slight chance (15-24%) of
thunderstorms Tuesday through the remainder of the week as
monsoonal moisture from the Southwest will likely (>60%
confidence) return to the region. Highest chances of showers and
thunderstorms will be over the mountains, especially the Blue
Mountains.

&&

.Preliminary Point Temps/PoPs...
PDT  57  91  56  91 /   0   0   0   0
ALW  63  93  62  93 /   0   0   0   0
PSC  60  95  59  94 /   0   0   0   0
YKM  57  92  58  94 /   0   0   0   0
HRI  60  93  60  94 /   0   0   0   0
ELN  55  84  56  91 /   0   0   0   0
RDM  49  91  51  93 /   0   0   0   0
LGD  56  94  56  94 /   0   0   0   0
GCD  53  96  55  96 /   0   0   0   0
DLS  59  89  61  95 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
WA...None.
OR...Red Flag Warning until 10 PM PDT Saturday for ORZ691.
     Air Quality Alert until noon PDT Monday for ORZ050-502-503-505-
     506-508.

&&

$$

DISCUSSION...86
AVIATION...75
FIRE WEATHER...86