329
FXUS66 KPDT 271712
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1012 AM PDT Sun Sep 27 2026

.KEY MESSAGES...
- Cloudy This morning with clearing west to east This
  Afternoon.

- Patchy Frost possible Tonight

- Rain overspreading the Washington Cascades Tuesday
  with gusty winds though the Gaps and Columbia Basin

&&

.DISCUSSION...
GOES satellite showed a southwest to northeast oriented jet-
stream across the Eastern Pacific into northern CA and across
the southeastern Oregon counties. North of this feature, a low
pressure was moving equatorward off the NW Pacific coast with
AirMass RGB indicating a swath of cold air across Washington and
the offshore region, with reds indicating the broader
PV/deformation zones moving toward the southern Oregon coast.

Clouds will continue to thicken through the day Today, with
clearing from west to east overnight. Longwave radiation cooling
will drop temps possibly as cold as the thirties in the
Kittitas Valley ( NBM shows the lower end of what is a
reasonable expected lows as the 25th percentiles of low temps in
the mid to upper 30s across the Kittitas/Yakima Valleys and
across the Lower Columbia Basin into central Oregon). The
spread leaves large uncertainty though as the 75th percentile
provides lows well into the mid 40s for most of these areas.
Its fair to say patchy frost risk overnight is possible given
the expected clearing sky.

NBM mean shows broad 20 knot surface winds across the Yakima
Valley, Simcoe Highlands and Columbia River Gorge/Lower Columbia
Basin of WA/OR Tuesday. This will be mainly a dry weather
system passage with the exception of the Washington Cascade
crest and Eastern Slopes as NBM shows small (less than 5%
confidence) chances for thunder across the Upper slopes, and
several tenth of an inch of QPF possible in those zones.
Good chances (50-85%) exist for wetting rains across the upper
slopes of the Washington Cascades Tuesday with chances for
rain in the eastern mountains are much low at level about 10%
or so. Low orographic shower chances lingers int he the
Washington Cascades through late week, as the flow becomes
zonal again across the area. Temperatures remains seasonal into
the 60s and 70s.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
VFR conditions will persist through the forecast period. Winds
will be light and variable through the period with mainly high
clouds.

&&

.Preliminary Point Temps/PoPs...
PDT  63  38  71  45 /   0   0   0   0
ALW  64  43  72  52 /   0   0   0   0
PSC  71  37  75  46 /   0   0   0   0
YKM  67  39  73  47 /   0   0   0   0
HRI  68  36  74  48 /   0   0   0   0
ELN  63  31  68  43 /   0   0   0   0
RDM  63  30  71  35 /   0   0   0   0
LGD  65  38  72  39 /   0   0   0   0
GCD  69  37  72  40 /   0   0   0   0
DLS  71  42  75  48 /   0   0   0   0

&&

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

&&

$$

DISCUSSION...71/95
AVIATION...90