879
FXUS66 KPDT 242331
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
431 PM PDT Sun Aug 24 2025

.UPDATED AVIATION.

.AVIATION...00Z TAFs...VFR conditions prevail through the period.
Although there`s a MVFR group for BDN/RDM in the overnight hours
as smoke from the Falls fire continues to impact parts of Central
OR. CIGs/VIS will be at their lowest in the early to late
morning. Other than that, winds will be light and variable for
most of the period with diurnal wind shifts.


.PREV DISCUSSION... /issued 147 PM PDT Sun Aug 24 2025/

DISCUSSION...An upper ridge of high pressure continues to sit
over the region today while the high pressure circulation has
pushed a plume of monsoonal moisture north into eastern OR.
Another round of cloud cover continues to push north across the
northeast OR and southeast WA this afternoon, with very light
showers having been noted along the southern edges of Deschutes,
Crook, and Grant counties.

Ensemble and deterministic guidance is in great agreement of the
upper ridge of high pressure sitting over the region through
Tuesday, though model guidance does depict a very weak low feature
developing offshore and undercutting the ridge tonight through
Tuesday. Tuesday night into Wednesday, an upper low in the
northeast Pacific will arrive offshore the PacNW, with the upper
ridge breaking down as this feature approaches the coastal PacNW
Wednesday morning. Ensemble cluster members are in much better
agreement than 24 hours ago with the upper low staying offshore
for Wednesday, then beginning to lift northeast into southern BC
Thursday into Friday. That said, about 54% of ensemble suite (GFS,
ECMWF, and Canadian) have the upper low lifting northeast second
half of Friday into Saturday, while the remaining about 46% are 12
hours earlier. Otherwise, after the upper low lifts across the
PacNW, the region will sit between another upper trough in the
northeast Pacific and upper ridging across the Desert Southwest.

Confidence remains moderate-high (70-85%) through at least Tuesday
that major to extreme HeatRisk with daytime temperatures 98-105
will continue to impact the Columbia Basin/Gorge and adjacent
valleys/foothills; while the moderate to low end major HeatRisk
with daytime temperatures 92-100 will impact central OR, the John
Day Basin, and intermountain valleys across northeast OR. By
Wednesday, ensemble guidance has high and low temperatures
decreasing into the upper 80s to mid 90s as the upper ridge
breaks down and pushes east of the region, overall reducing heat
impacts area-wide. Confidence is now moderate (60-75%) that
HeatRisk will become Moderate across the Columbia Basin/Gorge and
adjacent valleys/foothills Wednesday, likely resulting in heat
highlights ending early Tuesday night. The only uncertainty
surrounding temperatures will be cloud cover originating from
convective activity across southern and central Oregon today
through middle of next week, which could bring temperatures 2 to 5
degrees cooler than forecast in the afternoon but 3 to 7 degrees
warmer in the overnight periods.

Other than heat, the synoptic setup will allow monsoonal moisture
to creep north into the PacNW each day through Wednesday. The
increased moisture as well as forcing from daytime heating and
terrain influences will allow isolated thunderstorms to develop
across the mountainous terrain around central OR, including the
Cascade east slopes, and will spread to the remainder of the
mountainous terrain across northeast OR into southeast WA
(confidence 60-70%) and up the Cascade east slopes (confidence
40-60%) through the middle of the week. PWATs in the region will
gradually increase into the 0.85 to 1 inch range today through
the middle of next week, resulting in plenty of moisture for
heavier rainfall in the strongest thunderstorms. Current
confidence is moderate (60-70%) in afternoon to early evening
thunderstorm activity mainly across the mountainous terrain of
central/northeast OR and central/southeast WA throughout early to
mid next week. That said, confidence continues to be low (15-30%)
in the extent and strength of storms at this time. Showers and
thunderstorm activity will push off east Thursday and Friday with
dry conditions returning Saturday as the upper low swings inland
during this period. That said, the upper low will clip the WA
Cascades, resulting in a 10-20% chance of showers developing with
the low passage. Confidence is moderate-high (65-80%) that winds
will remain light to locally breezy into next weekend.

Lastly, a Red Flag Warning has been issued for the Oregon Fire
Weather Zones 700 & 704 for hot, dry, and unstable conditions
through Monday evening. These conditions will mainly threaten the
Flat fire, where more extreme fire growth could occur as the
inversion breaks in the afternoons. In the overnight periods, a
developing inversion will keep smoke near surface and will flow
south into the Redmond/Bend areas, creating reductions in air
quality and visibility.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  66  97  67  97 /   0   0  10  10
ALW  71  98  72  98 /   0   0  10  10
PSC  63 100  66 100 /   0   0   0   0
YKM  68 100  69  99 /   0  10  10  10
HRI  66 100  68 100 /   0   0  10  10
ELN  64  99  65  98 /   0  10  10  10
RDM  59  94  56  93 /  10  20  10  20
LGD  64  94  63  92 /   0  10  20  20
GCD  65  89  61  90 /  10  20  20  30
DLS  70 102  70 102 /   0  10  10  10

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Extreme Heat Warning until 9 PM PDT Wednesday for ORZ041-044-507-
     508-510.

     Heat Advisory until 9 PM PDT Wednesday for ORZ049-505-511.

     Heat Advisory until 9 PM PDT this evening for ORZ050-509.

     Red Flag Warning until 9 PM PDT Monday for ORZ700-704.

WA...Extreme Heat Warning until 9 PM PDT Wednesday for WAZ024-026>029-
     521-523.

     Heat Advisory until 9 PM PDT Wednesday for WAZ030.

&&

$$

SHORT TERM...82
LONG TERM....82
AVIATION...95