717
FXUS66 KPDT 051127
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
427 AM PDT Tue May 5 2026

.KEY MESSAGES...

- Above-normal temperatures and mostly dry conditions through
  the week

- Breezy to windy each day Wednesday through Friday through the
  Cascade gaps and across the Columbia Basin and Blue Mountain
  foothills

- Periods of low relative humidity and breezy to windy westerly
  winds Thursday and Friday through the Cascade gaps and across
  the Columbia Basin and Blue Mountain foothills

&&

.DISCUSSION...
Satellite imagery shows FEW-BKN mid-level clouds early this
morning over the Columbia Basin and vicinity, with mostly clear
skies elsewhere across the forecast area.

Zooming out to examine the bigger picture, water vapor imagery
reveals a ridge of high pressure offshore extending over the
Pacific Northwest and Canadian Rockies. Meanwhile, a closed low
is present over the Southwest and broad troughing is visible
downstream over the northern Great Plains and central to
northern Rockies.

A switch to northerly to northeasterly winds is forecast by
this afternoon across much of northeast Oregon and southeast
Washington. Temperatures are generally expected to be several
degrees cooler this afternoon relative to yesterday under the
"cooler" northerly flow aloft, but are still forecast to be
above normal for early May.

Regarding precipitation chances, 00Z and 06Z CAMs show isolated
showers developing this afternoon over the Cascade and Blue
mountains where modest instability (CAM-advertised MUCAPE of
250-750 J/kg) develops, but chances of measurable precipitation
are very low (5-15 percent) for any location so they have not
received a "slight chance" mention in the gridded forecast.

Looking ahead to Wednesday, NWP guidance is in good agreement
that a weak shortwave will ride over the top of the ridge across
British Columbia and the northern Rockies. This will induce a
decently strong cross-Cascade pressure gradient (8-12 mb between
PDX and GEG per latest guidance) and result in breezy to
locally windy westerly winds through the Cascade gaps and across
the Columbia Basin and Blue Mountain foothills. NBM
probabilities of exceedance show a medium-high (40-80 percent)
chance of reaching advisory-level wind gusts for
climatologically wind-prone locations within the aforementioned
region, with significantly lower chances elsewhere.

Another round of breezy, though likely (70 percent confidence)
not windy, conditions is forecast Thursday as upper-level
ridging rebuilds over the Pacific Northwest. That said, a drier
air mass is forecast to be present Thursday in the wake of the
shortwave, and locally low relative humidity (10-15 percent) is
forecast.

By Friday, ensemble mean 500-hPa heights and vorticity show
another shortwave from the Pacific entering the Pacific
Northwest. While ensemble clusters show notable variance in
strength and timing among solutions of the shortwave,
confidence remains high (70 percent) in another round of
widespread breezy to windy westerly winds through the Cascade
gaps and across the Columbia Basin and Blue Mountain foothills.
NBM probabilities of reaching or exceeding advisory-level wind
gusts are medium-high (40-80 percent) for wind-prone areas
within the region outlined above. Similar to Thursday, the dry
air mass (ensemble-advertised PWATs of 0.25-0.50") coupled with
sufficient downward mixing during the daytime should facilitate
some low relative humidity (10-15 percent) prior to the arrival
of a more humid air mass by later Friday.

Taking a glance at the weekend into next week, ensemble NWP
guidance shows little to no signal for organized precipitation
until Tuesday as upper-level ridging remains the favored
scenario for the bulk of the West. By Tuesday, 00Z ensemble
clusters suggest a low (25 percent) chance of a return to some
flavor of troughing for the region.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
VFR conditions with some mid- and high-level clouds and
diurnally/terrain-driven winds of 5-15 kts (gusty in the
afternoon) are forecast for the next 24 hours at all sites.

&&

.Preliminary Point Temps/PoPs...
PDT  78  50  83  54 /   0   0   0   0
ALW  78  53  82  56 /   0   0   0   0
PSC  83  51  88  54 /   0   0   0   0
YKM  83  53  87  52 /   0   0   0   0
HRI  83  51  85  55 /   0   0   0   0
ELN  78  50  79  49 /   0   0   0   0
RDM  78  43  81  43 /   0   0   0   0
LGD  73  46  78  49 /   0   0   0   0
GCD  75  45  78  46 /   0   0   0   0
DLS  83  56  83  54 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
WA...None.
OR...None.

&&

$$

DISCUSSION...86
AVIATION...86