780
FXUS66 KPDT 132341
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
441 PM PDT Wed Aug 13 2025

.Updated for Aviation...

.AVIATION...
00Z TAFS...Breezy winds are expected to continue through the
evening before decreasing. Most locations are gusting in the 25 to
30 kt range. Winds will decrease to 10 kts or less overnight,
except for DLS where it will remain gusty. Breezy winds are
expected again on Thursday, with gusts to around 20 kts in late
morning through the afternoon at all sites except YKM and PSC.

Otherwise VFR conditions are expected, though some local MVFR
conditions can not be ruled out from smoke.

&&

.PREV DISCUSSION... /issued 146 PM PDT Wed Aug 13 2025/

DISCUSSION...Satellite imagery this afternoon shows mostly clear
skies across the eastern PacNW, though road/fire cameras at the
surface show plenty of haze from blowing dust and smoke.

Today through Thursday: A dry upper shortwave and surface cold
front will move across the region, continuing to produce breezy to
windy conditions across the lower elevations. Strongest gusts up
to 50mph are expected to develop through the Kittitas valley and
along exposed ridges of the WA Cascade east slopes through late
this afternoon (confidence 80-90%). Relative humidities will also
dip below critical thresholds (10-20%) this afternoon, and
combined with the elevated winds, has resulted in widespread
critical fire weather conditions from central OR to the Columbia
Basin and adjacent valleys. While this system will remain dry,
there is a slight chance (15-25%) for light showers to develop
along the Cascade crest late this evening and into the overnight
hours. By tomorrow, broad troughing with weak flow aloft will
develop over the PacNW, with the forecast area remaining dry,
though temperatures will be on a cooling trend as a cooler airmass
advects into the region. Winds will remain breezy to locally
breezy in the lower elevations as pressure gradients will be slow
to weaken tonight and tomorrow.

Friday through Sunday: Confidence continues to increase (75-90%)
that a cooler, wetter pattern will develop across the PacNW
beginning with a cold front passage Friday into Saturday, with
several shortwaves/shortwave impulses swinging around the bottom
of a broad upper low in the Gulf of Alaska through Sunday. A weak
atmospheric river (AR) will accompany the passage of the cold
front, increasing PWATs to 0.7 to 1.1 inches across forecast
area, allowing for plenty of moisture to work with through the
weekend. As for convection, instability will be lacking across the
region for Friday, with low confidence (10-15%) that the cold
front will be enough to produce a thunderstorm or two across the
mountainous terrain. As for Saturday and Sunday, flow aloft will
back to the southwest, with surface based instability increasing
in the afternoon across central OR, OR Cascade east slopes, and
the eastern mountains. This will result in chances (15-30%) of
isolated to widely scattered thunderstorms to develop in the
afternoons and early evenings. With seasonably high PWATs across
the region, these thunderstorms will be capable of moderate to
heavy rainfall and small hail, with abundant lightning. While
lightning may be abundant, the increased rainfall with these
storms will keep the potential for new fire starts low. Moderate-
High confidence (70-85%) that temperatures will cool into the
upper 70s to mid 80s through the weekend.

Monday through Wednesday: Good agreement amongst ensemble cluster
members (ECMWF, GFS, Canadian) that upper level troughing will dig
equatorward off the west coast, increasing the southerly component
of flow aloft into the PacNW. By Monday, ensemble members begin a
drying trend across the forecast area, but keep modest instability
across the eastern mountains through Tuesday evening(confidence
55-75%). This will result in isolated thunderstorm chances
(10-20%) across the mountains each afternoon. With conditions
gradually drying out, these thunderstorms will likely be drier,
increasing the fire weather concerns going into the middle of next
week. By Wednesday, ensemble members are in good agreement of the
upper trough broadening over the eastern Pacific, and in turn
turning flow aloft more westerly and reducing the chances of
isolated thunderstorms over the eastern mountains (confidence
45-65%). Moderate confidence (50-70%) that temperatures will warm
back into the mid 80s with locally lower 90s early next week.
Lawhorn/82

AVIATION...Previous Discussion...18Z TAFs...VFR conditions to
prevail through the period. A layer of smoke coming from west of
the Cascades may produce periodic few-sct CIG readings across
northern TAF sites, but vsby impacts are not expected at this
time. Otherwise, west to northwest breezy winds will develop
across all sites 12-20kts with gusts up to 30kts today, with winds
becoming light after 3Z at sites RDM/BDN/YKM/ALW/PSC, and after
7Z for site PDT. Winds will persist at site DLS through the
period. Lawhorn/82

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  60  84  60  85 /   0   0   0  10
ALW  64  84  64  85 /   0   0   0  10
PSC  60  87  63  86 /   0   0   0  10
YKM  59  86  62  81 /   0   0  20  40
HRI  62  85  63  86 /   0   0   0  10
ELN  58  80  59  77 /   0   0  30  50
RDM  50  82  52  82 /   0   0   0  10
LGD  55  84  54  85 /   0   0   0   0
GCD  54  86  52  87 /   0   0   0   0
DLS  63  81  67  80 /   0   0  20  40

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning until 9 PM PDT this evening for ORZ691-693-701-
     702.

     Red Flag Warning until 11 PM PDT this evening for ORZ696-698-700-
     703>705.

WA...Red Flag Warning until 9 PM PDT this evening for WAZ690>694.

     Wind Advisory until 8 PM PDT this evening for WAZ026.

&&

$$

SHORT TERM...82
LONG TERM....82
AVIATION...77