900
FXUS66 KPDT 212330
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
430 PM PDT Thu Aug 21 2025

Updated Aviation Discussion

.DISCUSSION...A high pressure ridge will gradually replace the
zonal flow currently prevailing over the region, making for a
prolonged period of hot and dry conditions, potentially lasting as
long as the next week for the Columbia Basin and adjacent
valleys. As the PacNW finds itself wedged between a Four Corners
high and an oncoming Pacific low, the flow aloft will orient more
southwesterly, allowing for an injection of moisture and thus
thunderstorm chances across the mountains of central and eastern
Oregon. Ensembles broadly suggest a return to a more progressive
synoptic pattern by the following weekend, however a pattern
defined by ridging tilted negatively by an offshore low looks to
prevail through at least the midweek next week.

As the ridge axis starts to move in tomorrow into Saturday, this
transitory period will build enough of a pressure gradient Friday to
create breezy conditions across the east slopes of the Cascades,
namely from the Gorge down into central Oregon. The gradient isn`t
particularly strong, but could be enough to trigger critical fire
weather conditions in some spots. Have upgraded the Fire Weather
Watch in OR703 into a Red Flag Warning as a result, while dropping
the Watch for OR691, as it looks as though if critical conditions do
occur there, they`ll be too isolated to justify a Warning for the
entire zone. That, and conditions are admittedly already borderline,
and would need higher confidence in order to justify a partial zone
warning.

As far as heat headlines are concerned, an Extreme Heat Watch
remains in effect for the Columbia Basin, Gorge, and other adjacent
valleys starting Saturday, with the only change being to extend the
Watch out to Wednesday, as HeatRisk does suggest elevated heat
concerns could last perhaps beyond the midweek. Ensembles at the
very least suggest no significant change to the synoptic pattern
until at least next Thursday.

Can`t speak too much on storm chances mentioned earlier, as guidance
thus far suggests the threat won`t materialize until the latter half
of Sunday, but much can change this far out. Biggest source of
uncertainty will be in how this influx of moisture will interact
with this upcoming heat wave, which will certainly dry out of the
boundary layer. Deterministic guidance suggest PWATs climbing up to
an inch by Sunday evening, with an upper-level pattern that favors
orographic enhancement and instability, but will the storms that
materialize ultimately be wet or dry? Will have to see how CAMs
respond. Evans/74

.AVIATION...00Z TAFs...VFR conditions to prevail through the
period. Winds will be terrain-driven and 12kts or less at all
sites, with low chance (20-25%) chance of periodic afternoon gusts
around 20kts. Lawhorn/82


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  57  94  60  97 /   0   0   0   0
ALW  62  95  65  98 /   0   0   0   0
PSC  55  97  57 100 /   0   0   0   0
YKM  59  94  62  98 /   0   0   0   0
HRI  57  96  59  99 /   0   0   0   0
ELN  56  92  59  97 /   0   0   0   0
RDM  48  96  53  97 /   0   0   0   0
LGD  53  94  56  98 /   0   0   0   0
GCD  53  97  59 100 /   0   0   0   0
DLS  61  99  66 101 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Extreme Heat Watch from Saturday afternoon through Wednesday
     evening for ORZ041-044-507-508-510.

     Red Flag Warning from 2 PM to 11 PM PDT Friday for ORZ703.

WA...Extreme Heat Watch from Saturday afternoon through Wednesday
     evening for WAZ024-026>029-521-523.

&&

$$

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