226
FXUS66 KPDT 112302
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
402 PM PDT Tue Aug 11 2026

.Updated Aviation Discussion.


.KEY MESSAGES...
- Dry weather, seasonal temperatures, and breezy westerly winds
  through the Cascade gaps today.

- High confidence (70-95 percent) in a shift to a convective
  pattern Wednesday through the weekend.

&&

.DISCUSSION...
Water vapor imagery shows zonal (Washington) to quasi-zonal
(Oregon) flow over the forecast area early this morning. 00Z
and 06Z soundings at UIL/SLE/MFR and OTX, respectively,
corroborate satellite imagery with pure zonal flow aloft over
UIL/OTX and west to west-southwest flow aloft over SLE/MFR. Of
note, but perhaps of little consequence as far as today`s
weather is concern, a weak circulation is approaching the OR/CA
coastal border.

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. Regarding fire weather conditions, 00Z
HREF/REFS and latest NBM output suggest low chances (40% or
less) of overlapping critical wind/RH thresholds today; highest
probabilities are in the Kittitas Valley and lower Columbia
Basin of Oregon west of Boardman.

Looking ahead, ensemble NWP guidance suggests southwest flow
aloft amidst an amplifying 500-hPa height field Wednesday
through the remainder of the forecast period. This will
facilitate a change to a more convective pattern with daily
shower and thunderstorm chances, though analysis of ensemble
clusters reveals uncertainty in pattern details, especially
beyond Thursday. 00Z/06Z CAMs and the NBM indicate the best
shower and thunderstorm chances (5-20 percent) Wednesday and
Thursday over the Washington Cascades and limited portions of
the Blue Mountains. Shower and thunderstorm chances (10-30
percent) expand to encompass the Oregon Cascades and all of the
Blue Mountains by Friday and Saturday. By Sunday and Monday,
ensemble NWP indicates at least some potential (40-60 percent)
of a deep offshore closed low, strengthening southerly to
southwesterly upper-level winds, and ample moisture over the
forecast area; this solution is quite favorable for robust
convection. Fire Weather Watches may be needed if confidence in
widespread lightning increases.

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 /00Z TAFS THROUGH 00Z THURSDAY/...
VFR conditions currently across all sites, which will stay the
course through the period for most sites. KRDM is the only
terminal expected to drop to MVFR visibilities due to smoke
from nearby wildfires. Breezy winds of 10-15kts with gusts of
20-25kts for KDLS/KRDM through the evening before subsiding
later this tonight. 75

&&

.Preliminary Point Temps/PoPs...
PDT  54  85  52  84 /   0   0   0   0
ALW  60  87  58  86 /   0   0   0   0
PSC  57  90  56  88 /   0   0   0   0
YKM  59  89  58  87 /   0   0  10   0
HRI  58  88  55  87 /   0   0   0   0
ELN  56  83  54  82 /   0  10  30  20
RDM  46  84  43  82 /   0   0   0   0
LGD  53  88  52  85 /   0   0   0   0
GCD  53  89  52  86 /   0   0   0   0
DLS  61  83  59  87 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
WA...Air Quality Alert until 11 AM PDT Thursday for WAZ024-026>030-
     521>523.
OR...Air Quality Alert until noon PDT Wednesday for ORZ041-049-050-
     502-503-505-506-508>511.

&&

$$

DISCUSSION...86
AVIATION...75