500
FXUS66 KPDT 222307
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
407 PM PDT Fri Aug 22 2025

Updated Aviation Discussion

.AVIATION...00z TAFs...VFR conditions expected. Winds will
generally flow north to northeast during the day at 6 to 12 kts,
with some gusts up to 20 kts at some sites (namely PDT, RDM, and
BDN), before winds become light and terrain-driven overnight.
There is some area smoke/haze around RDM/BDN due to the Flat Fire
to the north, however with mostly VFR conditions observed thus
far today, confidence was not high enough to include mention of
any vsby reductions in the TAF. Mid-level sct cigs around 15 kft
are then expected to build in by tomorrow. Evans/74

&&

.PREV DISCUSSION... /issued 125 PM PDT Fri Aug 22 2025/

DISCUSSION...A ridge of high pressure continues to build over the
PacNW today, beginning a trend towards hotter and drier conditions
across the PacNW. Broad upper troughing will develop off the
western CONUS, resulting in a deep south to southwest flow. This
will allow monsoonal moisture rounding an upper high over the
Desert Southwest to push into OR and WA Saturday into Tuesday,
with increasing chances of isolated thunderstorms for the forecast
area starting Sunday. By Wednesday, ensemble cluster members agree
that the upper low offshore will swing inland while pushing the
upper ridge axis east of the forecast area. The upper trough will
continue to swing across the PacNW through Thursday, however, 33%
of members from the ECMWF, GFS, and Canadian ensemble suites favor
a slower passage, while another 55% favor the shortwave exit by
Friday morning.

With the upper ridge moving into the region, a slight pressure
gradient has developed, and will result in northeast winds along
the lee side of the Cascades. While winds will generally be
locally breezy (10-20mph) across the area, winds will be strong
enough and relative humidities low enough to result in critical
fire weather conditions developing this afternoon across the Warm
Springs Reservation. A Red Flag Warning continues to be in effect
for this area through this 11PM tonight.

The upper ridge has also resulted in the start of warming trend
that will persist through Wednesday as the upper ridge departs the
PacNW. Temperatures will be warming into the mid 90s to lower 100s
through Wednesday across much of the forecast area, while
overnight lows will be in the 60s. Concerning this time of year,
these temperatures are enough to trigger widespread high end
moderate to localized extreme HeatRisk across the lower
elevations, including the OR Cascade east slopes, Wallowa Valley,
and the Grande Ronde valley. With HeatRisk in the major category
across much of the Columbia Basin/Gorge and adjacent valleys, the
Extreme Heat Watch has been upgraded to a Warning, which is in
effect Saturday through Wednesday evening. Advisories have also
been issued for central OR, the John Day Basin, and the Grande
Ronde valley Saturday through Wednesday, while the Cascade east
slopes and the Wallowa valley are only in effect this weekend.
While hot temperatures are forecast, a fly in the ointment will
be cloud cover originating from convective activity across
southern Oregon starting as soon as Saturday night, which could
bring temperatures 2-5 degrees cooler than forecast in the
afternoon but 3 to 7 degrees warmer in the overnight periods. At
this time, confidence is low (20-25%) in timing, extent, and
impacts from any cloud cover developing Saturday into early next
week.

Speaking of convective activity, ensemble and deterministic
guidance indicate that with the arrival of monsoonal moisture to
the region, isolated thunderstorm activity will likely increase
south to north across the eastern half of OR/WA starting Sunday.
PWATs in the region will gradually increasing to the 0.85 to 1
inch range from Sunday into 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 is low (15-30%) in the extent and strength of storms at
this time. Will have a better idea once this time frame comes
within the CAMs window. Lawhorn/82

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  59  96  64  97 /   0   0   0   0
ALW  64  98  69  98 /   0   0   0   0
PSC  57  99  62 100 /   0   0   0   0
YKM  63  98  66 100 /   0   0   0   0
HRI  59  98  63  99 /   0   0   0   0
ELN  59  95  63  97 /   0   0   0   0
RDM  53  96  58  96 /   0   0   0   0
LGD  57  98  63  97 /   0   0   0   0
GCD  59 100  63  96 /   0   0   0  10
DLS  65 100  70 102 /   0   0   0   0

&&

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

     Heat Advisory from noon Saturday to 9 PM PDT Wednesday for
     ORZ049-505-511.

     Heat Advisory from noon Saturday to 9 PM PDT Sunday for ORZ050-
     509.

     Red Flag Warning until 11 PM PDT this evening for ORZ703.

WA...Extreme Heat Warning from noon Saturday to 9 PM PDT Wednesday
     for WAZ024-026>029-521-523.

     Heat Advisory from noon Saturday to 9 PM PDT Wednesday for
     WAZ030.

&&

$$

SHORT TERM...82
LONG TERM....82
AVIATION...74