424
FXUS66 KPDT 121207
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
507 AM PDT Wed Aug 12 2026

.KEY MESSAGES...

- Near-seasonal temperatures through the week.

- Breezy westerly winds through the Cascade gaps today.

- Transition to a convective weather pattern today with daily
  shower and thunderstorm chances into next week, mainly for the
  mountains.

&&

.DISCUSSION...
Water vapor imagery reveals a pattern transition in progress
with flow aloft turning southwesterly over the forecast area
early this morning; a weak trough is noted over the Pacific
Northwest, with an embedded shortwave diving southeast in the
vicinity of Vancouver Island. At the surface, a modest cross-
Cascade pressure gradient remains in place (4-6 mb difference
between PDX and DLS as well as SEA and ELN) which is keeping
breezy westerly winds in place through the Cascade gaps. As the
day progresses, gap winds will strengthen, reaching widespread
breezy to locally windy levels this afternoon.

NWP guidance is in excellent agreement that the shortwave
mentioned above will continue to track southeast into
Washington and northern Oregon today, serving as the synoptic-
scale catalyst for a slight chance to chance (15-35 percent) of
afternoon convection along the east slopes of the Washington
Cascades. Lower chances (5-10 percent) of showers and
thunderstorms extend across the Columbia Basin and portions of
the Blue Mountains.

The wave will then exit to the northeast into the northern
Rockies overnight into Thursday, albeit with a weak broad
trough remaining over the Pacific Northwest on Thursday in its
wake. Although PoPs are quite low, will mention that NWP
guidance is advertising synoptic-scale forcing coupled with
sufficient mid-level (700-500 hPa) moisture and negative mid-
level (700-500 hPa) theta-e lapse rates to facilitate some weak
nocturnal convection (predominantly showers with isolated
embedded thunderstorms) overnight into Thursday morning across
mainly the higher terrain of south-central Washington and
eastern Oregon.

Looking ahead, ensemble NWP guidance suggests continued southwest
flow aloft through the remainder of the forecast period. This
will keep a convective pattern in place resulting in daily
shower and thunderstorm chances, mainly over the mountains.
That said, analysis of ensemble clusters reveals significant
uncertainty in pattern details beyond Saturday. By Sunday and
Monday, ensemble NWP indicates roughly equal chances (40-60
percent) of a deep offshore closed low or a weaker open wave
trough. Either solution puts the forecast area under southerly
to southwesterly flow aloft, favorable for convection.

Fire Weather Watches may be needed if confidence in widespread
lightning increases this week or over the weekend.

Lastly, Air Quality Alerts/Advisories issued by air quality
agencies remain in effect for the majority of our forecast area
due to wildfire smoke from ongoing regional wildfires.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
VFR conditions are forecast through the period at all sites.
There is a very low chance (10 percent) of showers at YKM this
afternoon and evening. Diurnally breezy winds are forecast,
strongest at DLS/RDM/BDN/YKM in the afternoon and evening hours.
There is potential for smoke to induce sub-VFR conditions later
this afternoon through the overnight period at multiple sites,
but confidence was too low to forecast anything below 6SM at
this lead time.

&&

.Preliminary Point Temps/PoPs...
PDT  85  52  85  56 /   0   0   0   0
ALW  87  57  86  61 /   0   0   0   0
PSC  90  57  89  57 /   0   0   0   0
YKM  89  58  88  60 /   0  20   0  10
HRI  88  55  88  58 /   0   0   0   0
ELN  83  54  83  57 /  10  30  20  10
RDM  84  44  84  48 /   0   0   0   0
LGD  87  53  85  54 /   0   0   0  20
GCD  89  52  87  54 /   0   0   0  30
DLS  83  60  89  62 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
WA...Air Quality Alert until 11 AM PDT Thursday for WAZ026>030-
     521>523.
OR...Air Quality Alert until noon PDT today for ORZ041-049-050-502-
     503-505-506-508>511.

&&

$$

DISCUSSION...86
AVIATION...86