415
FXUS66 KPDT 162332
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
432 PM PDT Thu Oct 16 2025

Updated Aviation Discussion

.AVIATION...00z TAFs...VFR conditions expected. A weather system
moving into the region tonight will make for bkn-ovc cigs around
15-20 kft, followed by clearing conditions and an increase in
westerly winds Friday afternoon. Any precipitation associated with
this system is expected to remain in the mountains. Outside of
gusty winds in the DLS this evening, all other sites are expected
to see light and terrain-driven winds, before becoming W/NW
tomorrow afternoon and gusting up to 25 kts, especially at DLS and
PDT. 74

&&

.PREV DISCUSSION... /issued 250 PM PDT Thu Oct 16 2025/

DISCUSSION...Tonight through Friday, a shortwave passing across
the northern Rockies will clip the region, bringing a chance
(25-50%) of light rain showers to the Washington Cascade crest
with a slight chance (15-20%) farther south over the Oregon
Cascade crest; predominantly dry conditions are forecast
elsewhere.

The main weather concern associated with the system tonight
through Friday will be breezy to locally windy west to northwest
winds as cross-Cascade pressure gradients strengthen and
isentropic descent to the lee of the Cascades facilitates downward
momentum transfer to the surface. Additionally, while confidence
is only medium (50%), localized Red Flag conditions (overlap of
wind/low RH) may develop Friday afternoon through the Kittitas
Valley and also limited areas of the east slopes of the Washington
Cascade and Columbia Basin. Forecast soundings from some CAMs
indicate a layer of very dry air aloft, approximately between 850
and 700 hPa. The main question is if the dry air will be able to
mix all the way to the surface. If so, surface dew points in the
upper single digits to upper teens would result in significantly
lower RH compared to what is shown by NBM guidance.

Friday night into Saturday, confidence is very high (>90%) that a
temporary ridge of high pressure will move over the Pacific
Northwest. The main item to note will be poor to moderate overnight
RH recovery for mountain areas, especially the higher mountains.

The next chance of widespread precipitation will be associated
with a robust low-pressure system that is slated to arrive Saturday
into the weekend. A warm frontal passage is anticipated Saturday
morning through afternoon, passing from southwest to northeast.
Little to no precipitation is forecast with this front. A
southwest-to-northeast-orientied cold front will arrive Saturday
night through Sunday, sweeping from west to east. Frontal passage
is expected to bring breezy to windy conditions to the region,
with the best chances (30-70%) of reaching advisory thresholds
across our climatologically windy locations -- the Simcoe
Highlands, the Blue Mountain foothills, and portions of the
Columbia River Gorge and lower Columbia Basin. Snow levels will be
high enough to preclude snow at pass level, with the exception of
Sunday night into Monday as snow levels lower to 4500-5000 feet
behind the cold front.

Regarding uncertainty with the weekend system, while ensemble
clusters are in excellent agreement (>90% of members) that some
form of trough/low will move over the Pacific Northwest through
the weekend, they are still unsure on the form (fast-moving trough
versus slower-moving closed low) and how much precipitation the
region will get. The faster-moving trough solution is becoming
more likely (~85% of ensemble members) compared to the slower-
moving closed low (~15% of members). The former scenario would
lead to less precipitation, especially for the lower elevations,
and windier conditions through the Cascade gaps and into the
Columbia Basin.

Tuesday through Wednesday, not anticipating any significant
weather as ensemble NWP suggests a modest chance (35%) of a
shortwave traversing otherwise quasi-zonal upper-level flow over
the forecast area.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  41  65  34  64 /   0   0   0   0
ALW  45  64  39  62 /   0   0   0   0
PSC  40  69  34  60 /   0   0   0   0
YKM  40  66  34  59 /   0   0   0  10
HRI  42  67  35  62 /   0   0   0   0
ELN  39  59  30  56 /   0  10   0  10
RDM  34  64  28  70 /   0   0   0   0
LGD  37  63  31  65 /   0   0   0   0
GCD  36  64  32  69 /   0   0   0   0
DLS  47  66  40  63 /   0  10   0   0

&&

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

$$

SHORT TERM...86
LONG TERM....86
AVIATION...74