171
FXUS66 KPDT 192246
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
246 PM PST Fri Dec 19 2025

.DISCUSSION...Rest of today through Sunday: Zonal flow is setting
up over the PacNW this afternoon behind the exit of a surface cold
front and shortwave trough. Precipitation has tapered off across
much of the area during this transition, however snow showers have
developed along the WA Cascade crest, with shower activity
gradually dipping south along the northern OR Cascade crest.
Shower activity along the Cascade crest will increase throughout
the remainder of this afternoon and through the overnight hours as
a shortwave embedded in the zonal flow moves over the region,
bringing with it a period of moderate to heavy snow accumulations
into the Cascades and the northern Blues. Winter storm warnings
will remain in effect through tomorrow morning for the Cascade
east slopes as additional snow accumulations of 6 to 10 inches
falls over this area, while winter weather advisories will
continue through this evening and into the overnight hours as the
shortwave brings another 2-6 inches in the northern Blues as well.

Saturday, zonal flow will continue across the PacNW and result in
snow showers mainly the WA and northern OR Cascade crest, with
drier conditions across the remainder of the area throughout the
day. By Sunday, zonal flow aloft will become more southwest as a
trough swings out of the Gulf of Alaska, resulting in another
round of moderate to locally heavy mountain snow accumulations, a
light rain/snow mix then rain between 2kft to 4.5kft, and rain in
the remainder of the lower elevations.

Monday through Thursday: Ensemble guidance is in good agreement
through next week that upper level troughing will develop offshore
in the wake of the trough passage Sunday, with a general
troughing pattern persisting through the end of the period. That
said, disagreements do arise in the timing in the arrival/passage
of embedded shortwave troughs, leading to low confidence (25-40%)
in the details of precipitation amounts next week. That said,
confidence is moderate-high (55-80%) that snow levels will remain
low enough across the forecast area for each passing system to
bring mountain snow with a rain/snow mix in high desert valley
areas (e.g. Redmond-Bend areas) throughout the week. Of particular
note, ensemble cluster guidance is in good agreement of snow
levels lowering to the surface across the Blue mountain foothills,
Yakima/Kittitas valleys, and the portions of the Columbia Basin
Tuesday night through Wednesday morning, resulting in the
potential of snow in these areas (confidence 40-65%). That said,
each cluster solution depicts varying snow accumulation amounts in
these areas, with one solution (29% of members) showing at least 2
inches across most of the lower elevation areas outside of the
Lower Columbia Basin of WA, while the other solutions are
anywhere from a few hundreths to 1 inch. Other than snow impacts,
a handful of members (~10% of members) from the GFS and ECMWF
ensemble suites are hinting at strong winds (20-30 mph sustained
winds with gusts 35-50mph) developing across the forecast area
Wednesday as a surface low swings across Oregon. Confidence is at
least moderate (45-65%) that the forecast area will see breezy
conditions develop as the surface low impacts the region.
Lawhorn/82


&&

.AVIATION...00Z TAFs...Mostly dry conditions across the sites
persist with predominately VFR status. Slightly breezy at some
locations, especially PDT, RDM, ALW, PDT with 15 to 25 mph gusts,
with brief periods of 30 mph. Winds will remain somewhat breezy
through the period, but will slightly weaken as we head into the
later evening hours. YKM has PROB30 chances from some light snow
showers from 14Z to 18Z with MVFR conditions (that being the only
sub-VFR period currently forecasted out of all sites). Otherwise,
CIGs will remain high thanks to daytime mixing and stronger winds.


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  31  47  30  48 /  10  10  10  50
ALW  35  47  33  47 /  20  20  10  50
PSC  34  50  30  46 /   0  10   0  30
YKM  27  46  27  41 /  10  20  10  30
HRI  33  50  30  46 /  10  10   0  40
ELN  24  38  24  36 /  30  40  30  40
RDM  23  45  25  49 /  10   0  20  60
LGD  25  38  27  42 /  20  10  20  70
GCD  23  41  29  46 /  10   0  30  80
DLS  35  46  32  43 /  60  50  30  60

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 10 PM PST this evening for ORZ502.

     Winter Storm Warning until 10 AM PST Saturday for ORZ509.

WA...Winter Weather Advisory until 10 PM PST this evening for WAZ030.

     Flood Watch through late tonight for WAZ522-523.

     Winter Storm Warning until 4 PM PST Saturday for WAZ522.

&&

$$

DISCUSSION...82
AVIATION...95