010
FXUS66 KPDT 111112
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
412 AM PDT Tue Aug 11 2026

.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 /12Z TAFS THROUGH 12Z WEDNESDAY/...
Predominantly VFR conditions are forecast through the TAF
period. Winds will be diurnally and terrain-driven, breezy
through the Cascade gaps during the afternoon and evening hours.

Smoke from regional wildfires remains the biggest source of
forecast uncertainty with regard to potential for sub-VFR
CIGs/VSBYs. Anticipating another surge of smoke from wildfires
in the Cascades to affect BDN/RDM late afternoon and evening,
but did not have the confidence to advertise sub-VFR conditions
at the time of writing. Elsewhere, smoke from the Grasshopper
Fire has been lofted over PDT/ALW early this morning, and
surface smoke from the Hagen fire has remained northeast of
PDT.

&&

.Preliminary Point Temps/PoPs...
PDT  88  54  85  54 /   0   0   0   0
ALW  90  61  87  60 /   0   0   0   0
PSC  92  57  90  57 /   0   0   0  10
YKM  93  58  89  58 /   0   0   0  20
HRI  91  58  88  56 /   0   0   0   0
ELN  86  56  83  54 /   0   0  10  30
RDM  89  46  85  44 /   0   0   0   0
LGD  91  54  87  53 /   0   0   0   0
GCD  92  53  89  53 /   0   0   0   0
DLS  88  60  84  60 /   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...86