749
FXUS66 KPDT 241554
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
854 AM PDT Sun Aug 24 2025

.MORNING UPDATE...Isolated thunderstorms and showers have
developed across portions of south central OR, Ochoco John-Day
Highlands, Strawberrys, and the Southern Blues this morning, and
are expected to continue to develop into the afternoon hours.
Light rain and infrequent lightning will be possible with these
storms. Otherwise, hazy conditions from regional wildfire smoke
will impact the lower elevations again today, with mid to upper
level cloud cover spreading north into portions of the Columbia
Basin late this morning and afternoon. Have updated precipitation
and thunder chances across aforementioned mountain areas through
this evening, with rest of overnight forecast package on track.
Lawhorn/82


&&

.PREV DISCUSSION... /issued 1013 PM PDT Sat Aug 23 2025/

AVIATION...06z TAFs...Expecting mostly VFR conditions for the
forecast area, with sct mid-level cigs 10-15 kft and light,
terrain-driven winds less than 12 kts. BDN and RDM may
periodically see deteriorating conditions overnight due to smoke
from the nearby Flat Fire, however confidence is low in the
duration and extent of smoke. Most likely occurrence is during
the overnight hours, however. Evans/74

PREV DISCUSSION... /issued 512 PM PDT Sat Aug 23 2025/

DISCUSSION...An upper level ridge of high pressure has cemented
itself over the western CONUS today, while near surface flow
underneath has pushed a plume of monsoonal moisture northward
across NV and CA and up to the OR border at this time. Cloud cover
from overnight convection across northern NV/CA has continued to
push north into the forecast area, with area cameras showing
mostly virga showers underneath this cloud cover.

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 Sunday night
through Monday. Second Half of Tuesday into Wednesday, an upper
low in the northeast Pacific will push southeast towards the
PacNW, with the upper ridge breaking down as this feature
approaches the coastal PacNW. However, disagreement amongst
ensemble cluster members begin to increase Wednesday with the
location of the upper low offshore as well as timing of the upper
ridge breaking down. Disagreement amongst members continues
Thursday into the weekend in regards to the passage timing of the
upper low, as 44% of members have the upper low passing over the
PacNW Friday, while the other 56% of members show the upper low
becoming an upper wave and passing over the PacNW Thursday, and
into western Canada by Friday. The best agreement amongst these
solutions, however, is that the upper ridge will push east of the
region Thursday.

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 the heat impacts will lessen outside of the Columbia
Basin, with moderate confidence (65-75%) that widespread moderate
to major HeatRisk will continue to impact the Columbia Basin and
adjacent areas through Wednesday evening. As the upper ridge
departs sometime late Wednesday into Thursday, temperatures will
cool a few degrees, though afternoon temperatures will be in the
upper 80s to mid 90s (confidence 50-70%). 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 2-5
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 in the PacNW into the middle of next week. The
increased moisture as well as forcing from daytime heating and
terrain influences will allow isolated thunderstorms to develop
starting Sunday 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 35-50%) through the middle of the week. PWATs in the
region will gradually increase into the 0.85 to 1 inch range late
tonight through the middle of next week, resulting in plenty of
moisture for heavier rainfall in the strongest thunderstorms.
Current confidence is moderate (50-65%) 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.

Beyond Wednesday, confidence is low (15-25%) in the location,
extent, and timing of shower activity as the upper low swings
through the PacNW Thursday and Friday. Lawhorn/82

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  98  66  96  67 /   0   0   0  10
ALW  99  70  98  72 /   0   0   0   0
PSC 101  63 100  65 /   0   0   0   0
YKM 100  69 101  70 /   0   0   0   0
HRI 101  66  99  67 /   0   0   0   0
ELN  98  64  98  66 /   0   0   0   0
RDM  96  60  91  59 /  10  10  10  10
LGD  98  65  95  64 /   0   0   0  10
GCD  97  65  92  62 /  10  10  10  10
DLS 103  72 101  70 /   0   0   0   0

&&

.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 from noon today to 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...74