391
FXUS66 KPDT 111744
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1044 AM 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 /18Z TAFS THROUGH 18Z WEDNESDAY/...
VFR conditions currently across most sites, with the exception
of MVFR at KRDM due to reduced visibilities related to smoke
from nearby wildfires. This is expected to persist through the
day, improving slightly later this evening into the overnight
period as winds subside. Elsewhere, VFR conditions will prevail,
with breezy afternoon winds of 10-15kts and gusts of 20-25kts
for KDLS/KYKM. All other sites will experience light winds of
10kts or less under mostly clear skies. 75

&&

.Preliminary Point Temps/PoPs...
PDT  88  54  85  52 /   0   0   0   0
ALW  90  60  87  58 /   0   0   0   0
PSC  92  57  90  56 /   0   0   0   0
YKM  93  59  89  58 /   0   0   0  10
HRI  91  58  88  55 /   0   0   0   0
ELN  86  56  83  54 /   0   0  10  30
RDM  89  46  84  43 /   0   0   0   0
LGD  91  53  88  52 /   0   0   0   0
GCD  92  53  89  52 /   0   0   0   0
DLS  88  61  83  59 /   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