312
FXUS66 KPDT 271127
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
427 AM PDT Tue Oct 27 2026

.KEY MESSAGES...
- Persistent chances of mountain rain and snow through Thursday,
  with a Winter Weather Advisory in effect for the Upper East
  Slopes of the WA Cascades later tonight

- Breezy winds today and Wednesday

- Below normal temperatures through the weekend

&&

.DISCUSSION...Water vapor imagery tonight shows the PacNW
sitting between a departing upper shortwave trough to our east
and a shortwave trough diving down the PacNW coast. A modest
upper level jet has developed between the two systems and is
facilitating the passage of a shortwave impulse along the WA/OR
state border. Per nighttime satellite imagery and radar returns,
light to moderate rain showers have developed along the OR/WA
border, with showers banking up against the Northern Blues.

Today through Friday: The passage of yesterday`s upper
low/trough started a prolonged period of the PacNW remaining
under the influence of a broad troughing/low pressure pattern
that`ll persist into the weekend (confidence 85-95%). The
approaching shortwave trough offshore the PacNW will bring
reinforcing rain/snow chances across most of the eastern
mountains into the afternoon. As the shortwave trough pushes
into ID late this afternoon, shower chances will diminish
across the eastern mountains while rain/snow chances continue
across the Cascades and northern Blues.

Later this evening, a second upper closed low will develop over
central BC, then remain parked just offshore WA Wednesday
afternoon through Friday. The arrival of the upper low to the
PacNW will result in a cooler airmass filtering into the region,
with snow levels lowering from around 5-5.5kft this morning to
3.5-4.5kft by tomorrow morning. Increased shower activity ahead
of the low later this evening and overnight will result in snow
accumulations between 3-7 inches above 4kft in the WA Cascades,
with accumulations generally 1-3 inches above 5kft in the OR
Cascades, Elkhorn Crest, Eagle Caps, and interior northern
Blues(confidence 65-85%). A Winter Weather Advisory is
currently in effect for the Upper East Slopes of the WA Cascades
this evening through tomorrow afternoon.

Light mountain snow/rain showers will continue through Friday as
the upper low remains parked offshore. However, any additional
accumulations through Friday will be very light, with 48-hr
probabilities of snow accumulations exceeding 2 inches
only 30-60% along portions of the Cascade crest, with chances
closer to 10-20% or near zero over the Blues, Wallowas, and mid
slopes of the Cascades.

Otherwise, the parade of upper low pressure systems through the
region will result in afternoon temperatures lowering into the
50s by tomorrow, then lower further into the mid 40s to low 50s
Thursday/Friday (confidence 65-90%). Breezy winds (15-25mph
with gusts to around 35mph) will develop through the Cascade
Gaps and lower elevations today with the shortwave passage,
then mainly across central OR to the Columbia Basin Wednesday
with the approach of the second closed low (confidence 65-80%).

Saturday through Monday: Ensemble guidance is in agreement of
the upper closed sliding inland starting Friday night into
Saturday, with continued chances of light rain/snow in the
mountains through at least Saturday. Overall, there is good
agreement amongst ensemble members that by Monday, an upper
ridge will slide over the PacNW with widespread dry conditions
developing (confidence 45-60%). However, late Saturday through
Sunday there is disagreement in how quickly the upper trough
moves out of the region, as well as disagreement in the strength
of the incoming upper ridge. Confidence in precipitation chances
late Saturday into Sunday is low (15-20%), while there is
moderate confidence (45-60%) in the forecast late Sunday into
early next week. Lawhorn/82

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...VFR conditions to
prevail through the period. Showers moving through the area will
continue to impact sites DLS/PDT/ALW through this morning, while
there is a prob30 chance that sites RDM/BDN will see shower
impacts between 16-19Z. While chances are low (<30%), CIGS/vsby
may decrease to MVFR or lower within shower activity. Winds will
generally be light, 12kts or less, through the period...except
at site DLS where winds will increase to 12-17kts with gusts to
around 25kts between 21Z-02Z. Lawhorn/82

&&

.Preliminary Point Temps/PoPs...
PDT  55  33  52  31 /  40  20  40  20
ALW  55  39  51  34 /  70  40  70  30
PSC  61  37  57  30 /  10  10  30   0
YKM  60  33  55  30 /   0  20  30   0
HRI  59  37  55  29 /  10   0  20   0
ELN  54  28  48  21 /  10  60  60  10
RDM  47  28  47  19 /  40   0  10   0
LGD  50  31  50  27 /  70  50  40  50
GCD  47  29  48  27 /  50  20   0   0
DLS  59  39  55  32 /  30  70  90  40

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
WA...Winter Weather Advisory from 5 PM this afternoon to 5 PM PDT
     Wednesday for WAZ522.
OR...None.

&&

$$

DISCUSSION...82
AVIATION...82