438 
FXUS66 KPDT 282238
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
338 PM PDT Sun Sep 28 2025

.DISCUSSION...Today through Tuesday: Current satellite and radar 
imagery show mostly clear skies across the forecast area with few 
clouds lingering. Warm and dry conditions prevail today, but with 
light to breezy winds over the Cascade Gaps and eastern mountains 
from the low-level upslope flow through this evening. Monday onward, 
the frontal system will move across the PacNW with widespread 
showers. The raw ensembles favor a 60-80% probability for amounts up 
to 0.15 inch over the WA/OR Cascades and 30-50% prob of rain amounts 
of 0.25 inch for the eastern mountains Monday. Tuesday seems to have 
the raw ensembles slightly lower with a 40-60% prob for 0.25 inch. 
Otherwise, the lower elevations will have 0.10 inch or less. This 
system will assist in bringing isolated thunderstorms upward across 
portions of the East Slope of OR Cascades and eastern mountains for 
Monday and then the Wallowas Tuesday (<20% chance). The HRRR, RAP, 
and NAM models suggest marginal instability (<500 J/Kg of MUCAPE, LI 
of -2 to 1, low 1km wind shear) for both days, along with the HREF 
having less than 30% probability of thunder Monday over the eastern 
mountains. Overall, we are looking to see potential discrete storms 
for Monday and Tuesday, though with low chances on severity. Breezy 
winds at 15-25 mph will develop across the Cascade Gaps Monday and 
Tuesday during afternoon into evening hours from the strong surface 
pressure gradients due to the passing frontal system. 

Wednesday through Saturday: The low pressure system, over the 
southern British Columbia coast, pushes the frontal system across
the PacNW thus bringing another round of widespread showers. 
Isolated thunderstorms may develop over the crest of WA/OR 
Cascades Wednesday afternoon into evening. However given the weak 
instability, chances will be on the low-end (<20%). Other than 
that, it seems like that we will have mainly showers across the 
forecast area through Friday (30% confidence). Rain amounts might 
reach up to 0.10 inch or more at the Cascades Wednesday with 
everywhere else below 0.05 inch. The rain amounts will then 
slightly decrease Thursday into Friday morning, but increases up 
to 0.10 inch over the Wallowas (<40% confidence). Dry conditions 
will return Friday night onward. Winds will also be breezy up to 
20 mph Wednesday across the Cascade Gaps as the system passes, but
may gradually decrease Thursday into the weekend. Feaster/97
  

&&


.AVIATION...18Z TAFS (Previous Discussion)...VFR conditions prevail 
throughout this period. The upslope flow will strengthen the surface 
pressure gradients for breezy winds to briefly develop this late 
morning through afternoon at KRDM/KBDN, sustaining up to 10kts with 
gusts of 15-20kts. The remaining sites will have terrain-driven 
winds less than 12 kts. Feaster/97

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  54  78  52  74 /   0  20  70  20 
ALW  59  78  56  74 /   0  10  70  30 
PSC  52  78  52  75 /   0  20  50  20 
YKM  54  76  49  71 /  10  40  60  30 
HRI  54  79  52  75 /   0  20  60  20 
ELN  51  72  44  68 /  10  40  70  30 
RDM  49  72  41  69 /  10  50  60  20 
LGD  52  78  50  72 /  10  20  80  30 
GCD  52  75  47  71 /   0  50  70  10 
DLS  59  74  53  73 /  10  60  60  40 

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
&&

$$

SHORT TERM...97
LONG TERM....97
AVIATION...97