861
FXUS66 KPDT 022240
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
240 PM PST Sun Nov 2 2025

Updated Aviation Discussion

.DISCUSSION...

KEY POINTS

1. Snowfall potential for the Washington Cascades Monday through
   Monday night

2. Generally wet, active weather pattern through the week

3. Breezy to windy Tuesday night through Friday

Satellite imagery shows the genesis of our next weather system,
slated to arrive Monday morning, developing in the Pacific Ocean
as a shortwave interacts with a pre-existing baroclinic zone in
the vicinity of 36N, 140W. While ensemble NWP guidance is still
displaying a range of solutions with regard to the depth (995-1005
hPa) and track of the surface low that is anticipated to develop
through the day, confidence in precipitation for the forecast area
Monday through Monday night is high (60-95 percent) for the
Washington side of our CWA and medium (30-60 percent) for the
Oregon side.

Of particular interest is potential snowfall for the Washington
Cascades and their east slopes above 2500 feet on Monday.
Precipitation, and also snowfall, will be modulated by the track
of the surface low, which ensemble solutions take up the Oregon
coast and then inland across either western Oregon or western
Washington Monday through Monday night. Forecast soundings from
12Z CAMs show low-level southeasterly to easterly upslope flow
beneath a favorable coupling of the divergent jet entrance at
250-hPa and divergent jet exit at 700 hPa. In tandem with an
injection of modest moisture -- IVT of approximately 250-500
kg/m*s -- this should facilitate a good setup for precipitation
along the Washington Cascades and their eastern slopes. Have held
off on any winter weather highlights for the Cascades for a couple
reasons. Forecast temperatures are marginal (31-34 degrees minimum
from 12Z HREF soundings, and warmer in the NBM) for accumulation
on paved surfaces during the day. Moreover, NBM probabilities of
24-hr snowfall exceeding advisory levels (5 inches for the lower
slopes and 6 inches for the upper slopes) are low-medium (20-40
percent) for mountain passes (White, Snoqualmie, and Blewett) from
12Z Monday through 12Z Tuesday. That said, snow levels could (10
percent chance per NBM guidance) drop as low as 2500 feet should
the right scenario pan out; namely, a persistent band of moderate
to heavy precipitation with rate-driven cooling of low-level and
surface temperatures. Snow levels are anticipated to rise above
pass level from south to north Monday night through Tuesday as
low-level flow turns southwesterly and warmer air is advected into
the region.

Tuesday night through Wednesday, ensemble guidance is in good,
though not excellent, agreement that a negatively tilted trough
will approach the Pacific Northwest, with multiple shortwave
impulses wrapping around its base and traversing the forecast
area. Another round of moisture will be transported inland with
this system, resulting in periods of likely (55 percent or higher)
PoPs area-wide. Predominantly southwesterly flow aloft during the
period will likely (75 percent confidence) preclude snow levels
dropping low enough to warrant any winter weather headlines.

Aside from precipitation, tangible weather will be dominated by
breezy to windy southeasterly winds Tuesday night through
Wednesday morning across the Blue Mountains region, then more
widespread southwesterly winds Wednesday afternoon through Friday.
Confidence is currently 60 percent in near-advisory or advisory-
level wind gusts (45 mph or greater) along the slopes of the
northern Blue Mountains Tuesday night into Wednesday morning, with
confidence ranging from 30-50 percent in advisory-level gusts
elsewhere across central and eastern Oregon each day Wednesday
through Friday.

.AVIATION...00Z TAFs...VFR conditions to prevail through the
period. CIGs of bkn-ovc will increase this evening and overnight
as a weather system approaches the region. CIGs will lower to
around 10kft by tomorrow morning, with precipitation mainly
confined to the Cascade crest. Light rain will arrive to sites
YKM/DLS by the afternoon, with light rain continuing into the
early evening. Best chances of light rain won`t be until at or
after 00Z at all other sites. Winds will be light, 12kts or less,
through the period. Lawhorn/82

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  34  47  37  56 /   0  50  90  40
ALW  37  47  40  55 /   0  60  90  50
PSC  36  50  37  53 /   0  40  80  30
YKM  36  49  36  50 /   0  50  80  50
HRI  36  48  38  55 /   0  50  80  30
ELN  31  46  33  47 /  10  50  80  50
RDM  27  56  36  59 /   0  40  70  30
LGD  29  54  40  59 /   0  50  90  50
GCD  33  61  44  60 /   0  30  80  40
DLS  40  51  42  55 /   0  70  90  60

&&

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

$$

DISCUSSION...86
AVIATION...82