751
FXUS66 KPDT 131023
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
323 AM PDT Mon Oct 13 2025

.DISCUSSION...

Key Messages:

1. Mountain snow continues this morning.
   *Winter Weather Advisories Active*

2. Frigid morning temperatures Tuesday.
   *Freeze Warnings Issued*

3. Warming trend Wednesday onward, showers return Saturday.


Current radar and infrared satellite imagery shows light to
moderate returns extending across the Columbia Basin, Blue
Mountain foothills, Cascades, and the Yakima/Kittitas Valleys
under cloudy to mostly cloudy skies. This is in response to an
upper level low pressure system dropping south along the
Washington and Oregon coasts this morning, which has brought
continuous mountain snowfall as snow levels have dropped to
3500-4500 feet. 4 inches of snowfall has been observed at White
Pass, with a dusting also noted via webcams over Snoqualmie Pass.
Snowfall will slowly taper off this afternoon and early evening
as the upper level system continues south and moves onshore over
Central California later today. As a result, Winter Weather
Advisories are still active until 1 PM today across the Cascades
for elevations above 4000 feet as an additional 2 to 4 inches of
snowfall is possible. Light rain has also been persistent at
lower elevations of the Basin and across the Blue Mountains, where
amounts have reached 0.20-0.30" in the last 12 hours. Lower
amounts of 0.05-0.15" are observed through Central Oregon, the
Tri-Cities area, and Yakima/Kittitas Valleys. These areas can
expect an additional 0.01-0.05", with higher elevations along the
Southern Blue Mountains and the John Day Highlands expected to
receive another 0.05-0.10" of rain through the day.

As the upper level low pressure continues to drop south along the
northern California coast later today, north winds will persist
across the area to usher in a drier and cooler airmass that will
promote effective radiational cooling overnight into Tuesday
morning. Tuesday morning temperatures over the Kittitas Valley,
Simcoe Highlands, and the Blue Mountain foothills of Oregon are
expected to drop below freezing, with isolated pockets dipping
into the upper 20s. Thus, the Freeze Watch originally issued for
the Kittitas Valley has been upgraded to a Freeze Warning and
expanded to include the Simcoe Highlands and the Blue Mountain
foothills of Oregon, active between 11 PM today through 9 AM
Tuesday morning. Confidence in temperatures dropping to or below
freezing is high moderate to high (60-90%) via the NBM for these
regions, but highest (85-95%) across the northern Blue Mountains
foothills of Oregon. This is related to two limiting factors of
the timing of clearing cloud cover (Southern Blue Mountain
foothills) and confidence in low winds (Simcoe Highlands). A later
or non-clearing sky would relate to warmer temperatures as
radiational cooling would be hampered as heat would be trapped
closer to the surface, and elevated winds would also relate to
better mixing in the lower atmosphere. The NBM suggests a 30-40%
ensemble spread related to overall cloud cover early Tuesday
morning across the Southern Blue Mountain foothills, with the 75th
percentile indicating 44% cloud cover. The spread associated with
overnight winds across the Simcoe Highlands indicated a value of
16 mph, with a 75th percentile of 21 mph. While both cloud and
wind 75th percentile values are not expected and below the current
forecast, it is worth noting as they are related to overall
confidence and model performance. Other deterministic and ensemble
guidance (GFS, ECMWF, CAN, etc.) have been consistently trended
Tuesday morning temperatures downward each model run over the last
3-4 days, adding confidence to the freezing potential for low
temperatures Tuesday.

The upper level low pressure moves onshore over Central California
Tuesday afternoon and into Nevada Wednesday morning as an upper
level ridge of high pressure builds in from the coast. Winds will
become more onshore and from the west, allowing more normal
temperatures to return on Wednesday with highs reaching into the
low to mid-60s across the Columbia Basin. Ensembles do suggest a
weak shortwave passing to our north late Thursday into Friday,
allowing for a chance (30-40%) of mountain precipitation across
the Cascades as snow levels hover between 5500-6500 feet.
Temperatures are expected to peak on Friday, with highs in the low
to mid-60s across the Columbia Basin. A more substantial system
looks to approach the coast over the weekend, bringing a return to
widespread precipitation Saturday night through Sunday. Ensembles
still struggle with system strength and timing so confidence in
specific rain amounts is rather low (10-30%) at this time, but
elevated rain chances (45-65%) and snow levels of 5000-6000 feet
are expected. 75



&&

.AVIATION...06Z TAFs...Rain showers continue to impact most sites
with low cloud decks of around 4000-5000 feet. Some of the heavier
bands gave some sites brief MVFR/IFR conditions. At least a small
chance remains through the night for all sites (5-15% chance) for
brief MVFR/IFR conditions with the heavier bands of rain occur.
As temperature drops overnight, we can expect some areas to
approach at/near saturation with light winds. This could produce
VIS and CIG issues in some areas. Confidence is not high for
widespread/longevity sub-VFR conditions, so PROB30 groups for
MVFR have been put in for PDT/ALW for the early morning hours
tomorrow. DLS/RDM/BDN will see MVFR conditions thanks to lowering
cloud decks of around 2500 feet.



&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  55  33  55  34 /  50  10  10  10
ALW  58  36  56  37 /  40  10  10  10
PSC  61  35  60  32 /  50   0   0   0
YKM  54  33  60  32 /  80   0   0   0
HRI  58  35  58  33 /  60   0   0  10
ELN  52  29  59  29 /  80   0   0   0
RDM  48  27  52  24 /  50  10  10  10
LGD  53  33  58  32 /  60  10  20  10
GCD  54  33  57  30 /  60  10  20  10
DLS  56  38  62  38 /  60   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Freeze Warning from 11 PM this evening to 9 AM PDT Tuesday for
     ORZ507-508.

     Winter Weather Advisory until 1 PM PDT this afternoon for ORZ509.

WA...Freeze Warning from 11 PM this evening to 9 AM PDT Tuesday for
     WAZ026-521.

     Winter Weather Advisory until 1 PM PDT this afternoon for WAZ522.

&&

$$

SHORT TERM...75
LONG TERM....75
AVIATION...95