952
FXUS66 KPDT 201719
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1019 AM PDT Mon Jul 20 2026

.KEY MESSAGES...
- Upper level ridging over the region will bring a warming and
  drying trend across the forecast area, with high end moderate
  to major HeatRisk developing in and around the Columbia Basin

- Monsoonal moisture push with shortwave impulses will result in
  a return of isolated to scattered thunderstorm activity across
  central OR and the northeast OR mountains

- Upper level troughing offshore will produce breezy winds in
  the Cascade Gaps and Columbia Basin Thursday into the weekend

&&

.DISCUSSION...
Satellite imagery tonight shows mid to upper
level cloud cover spreading north and east across the forecast
area, with regional radar showing very light returns from
Deschutes county to Baker county. This cloud cover is associated
with a shortwave impulse that is pushing into southern OR and
is forecast to ridge overtop an upper ridge over the PacNW.

Sensible weather concerns through the middle of the week will
revolve around a strengthening upper level ridge producing hot
temperatures in and around the Columbia Basin; the upper ridge
will shift east Wednesday into Thursday, allowing monsoonal
moisture and shortwave impulses to move across the forecast area
and produce isolated to scattered thunderstorm chances.

Through early Thursday, the PacNW will see an upper level ridge
of high pressure gradually strengthen each day while deep
southerly flow persists aloft. This will introduce increasingly
hot temperatures across the lower elevations, with the brunt of
the heating expected in the Columbia Basin/Gorge and adjacent
foothills/valleys through Thursday. Portions of the OR/WA
Columbia Basin and the eastern Gorge will reach the 100 degree
mark as early as Tuesday afternoon, with the Blue Mountain
foothills, Yakima/Kittitas valleys, portions of north central
Oregon, and portions of the John Day Basin reaching 100 degrees
Wednesday(confidence 70-90%). These temperatures will continue
in most of these areas Thursday, however increasing winds
through the Cascade Gaps late afternoon may limit heating
through the eastern Gorge and the Kittitas valley (confidence
60-70%). Between elevated afternoon and overnight temperatures,
HeatRisk values across much of the lower elevations will be in
the moderate to major categories starting Tuesday, with
increasing confidence (70-80%) that heat highlights will be
needed.

From now through the middle of the week, ensemble and
deterministic guidance depicts a monsoonal moisture push riding
the southerly flow into the intermountain PacNW, with PWATs
rising to around 0.75 to 1.25 inches by this afternoon. However,
activity isn`t expected to develop until Wednesday when the
upper ridge begins to push east, allowing shortwave impulses to
lift across the forecast area. On Wednesday, the main
thunderstorm activity will be focused across central OR and the
mountainous terrain from the Cascade east slopes to the Elkhorn
crest. In these areas, MUCAPE will be between 500-1000J/kg, low
level lapse rates 8-10 C/km, and 0-6km shear between 20-40kts.
These conditions will be enough for thunderstorms to develop in
the afternoon and become organized as they propagate north. By
Thursday, similar conditions will be present along the WA
Cascades, Blue Mountains, and Wallowa county. Expect at least
small hail, gusty outflow winds, frequent lightning, and a few
storms to produce heavy downpours.

Late Thursday through the weekend, there is good agreement
amongst ensemble cluster guidance that weak upper troughing will
develop off the coast of the PacNW while upper level ridging
pushes east and south. Southwest flow aloft will push prevent
monsoonal moisture from advecting into the region, resulting in
drying conditions across the forecast area. The proximity of the
upper trough Friday and Saturday will also result in breezy west
to northwest winds(15-25mph with gusts 25-40mph) through the
Cascade gaps and across the Columbia Basin. Confidence is
moderate (45-65%) that peak winds will overlap with critically
low RHs in portions of the Columbia Basin and Cascade Gaps
Friday and Saturday, resulting in elevated fire weather
conditions those days. By Sunday, there remains good agreement
that the trough will retrograde into the northeast Pacific,
resulting in weaker Cascade gap winds (confidence 40-50%).
Lawhorn/82

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Overall, VFR conditions prevail with general light winds across
the area, with occasional breezy winds across Central Oregon.
Wildfire smoke is still prominent across the area. Near/at
surface smoke across the Oregon TAF sites will drop visibility
in MVFR to IFR, with smoke mixing in by the afternoon hours.

&&

.FIRE WEATHER...
Conditions will remain hot and dry into the
middle of the week, with hottest conditions in the Columbia
Basin and adjacent foothills/valleys. A shift in upper level
ridging to the east will introduce increasing isolated to
scattered thunderstorm chances. Wednesday, chances will be
focused across central OR and the eastern mountains. Chances
Thursday will be focused along the WA Cascade crest, Blue
Mountains, and Wallowa county. Thunderstorms will be capable of
frequent lightning, gusty outflow winds, small hail, and brief
heavy downpours. Winds will increase through the Cascade Gaps
and Columbia Basin Friday and Saturday, and are expected to
overlap with critically dry conditions. Expect elevated to
critical fire weather conditions those days. Lawhorn/82

&&

.Preliminary Point Temps/PoPs...
PDT  88  62  96  66 /   0  10   0   0
ALW  91  67  99  71 /   0  10   0   0
PSC  92  65 100  68 /   0  10   0   0
YKM  92  68  99  70 /   0   0   0   0
HRI  91  66  99  70 /   0  10   0   0
ELN  90  65  97  68 /   0   0   0   0
RDM  87  58  93  62 /  20  10  10  10
LGD  92  62  97  66 /  10   0   0  10
GCD  92  59  95  63 /  10   0   0  10
DLS  92  69 101  73 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
WA...Extreme Heat Watch from Tuesday morning through Thursday
     evening for WAZ024-027>029.
OR...Extreme Heat Watch from Tuesday morning through Thursday
     evening for ORZ041-044-507.
     Air Quality Alert until noon PDT today for ORZ050-502-503-505-
     506-508.

&&

$$

DISCUSSION...82
AVIATION...95
FIRE WEATHER...82