087
FXUS66 KPDT 111026
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
326 AM PDT Tue Mar 11 2025

.SHORT TERM...
Today through Thursday...Westerly flow across the area early
today, will become southwesterly late this afternoon and tonight.

Precipitation will begin to move onshore in the southwesterly
flow and POPS are expected to increase into Wednesday, in advance
of a broad trough which will move onshore Thursday. Precipitation
chances look to be highest Wednesday night into Thursday morning,
with another shot Thursday afternoon.

Snow levels on Wednesday will initially start out quite
high...around 3500 feet in the Washington Cascades and 4500 feet
to 5500 feet in the Oregon Cascades and over 5500 feet elsewhere.

However, snow levels will drop during Thursday as the trough moves
inland with the Washington Cascades dropping below 2000 feet and
the Oregon Cascades dropping to around 2000 feet.

QPF Wednesday into Thursday will be 0.50 inches to 0.75 inches in
the mountains with 0.75 to 1.00 inches along the crests. most
lower elevation locations will generally see around 0.25 inches,
with some of the drier valley areas seeing less.

A Winter Weather Advisory has been issued for Wednesday night into
Thursday for the Oregon Cascades, for areas above 4000 feet.
Guidance suggests there could be 5-8 inches of snow, especially
around Santiam Pass. Working against us is time of year, but with
an unseasonably cold trough and rapidly falling snow levels it
doesn`t seem difficult to reach advisory criteria. Additionally,
with winds gusting around 35 mph, any snow may blow around.

For the Washington Cascades, there will be snow as well, but
mainly along the crests, with perhaps 3 to 4 inches at pass
level.

With the trough moving onshore Wednesday night into Thursday, it
will become breezy, with winds gusts expected in the 15 to 20 mph
range in almost all areas, many in the 20 t0 30 mph range and
some higher, especially across the Ochoco-John-Day Highlands and
Eastern Oregon. The NBM probabilities of wind gusts >=25 mph is
anywhere from 60 to >90 percent over much of the area, with the
exception of the Columbia Basin and Gorge and Yakima Valley.
However, the probabilities of wind gusts >=39 mph is only 50 to
about 70 percent and confined to the higher terrain of the Ochoco
John Day Highlands and the higher terrain of eastern Oregon.
Stronger winds are expected Thursday. Wnd gusts across the
Columbia Basin, Blue Mountain Foothills, Cascade Gaps, Simcoe
Highlands will be in the 20 to 30 mph range, possibly as high as
35 mph. The NBM probabilities of wind gusts >=39 mph generally
range from about 50 to 70 percent.

.LONG TERM...
Key Messages:

1) Dry conditions starting the long-term.
2) Back-to-back trough systems coming through the weekend.
3) Mountain snow and low-level rain pattern.

A back-to-back wave of trough systems over the weekend going into
early next week will define the active weather pattern ahead. Upper
level winds will become more zonal/westward Thursday night into
Friday morning after upper-air troughing associated with a cold
front passes through the PacNW into the Idaho region. This will inhibit
 precip chances for the majority of the CWA and limit additional
QPF to the eastern slopes of the Cascades. NBM currently shows an
additional 1-3 inches of snow for the Cascade regions during the
transition of another short wave digging in the Pacific into the PacNW
region Friday afternoon/early evening. Due to the on- going storm from
the short period and the continuation of precip, a Winter Weather
Advisory has been issued for the Eastern Slopes of the Oregon
Cascades until 10PM Thursday.

Model guidance and clusters show good agreement Friday going into Saturday
of this shortwave impacting the area with moderate to heavy mountain
snowfall across the Cascades and Blue Mountains. As the system passes,
snow levels will decrease to 1000 to 1500 feet in the early morning
of Friday, increasing to 1500 to 2000 feet later in the day. Amounts
expected vary depending on location. Confidence and amounts expected
are as follows:

Lower elevations: up to an inch (70-90% confidence)
Central OR: 1-3 inches (50-70% confidence)
Northern Blue Mountains: 6-10 inches (60-80% confidence)
Cascades: 6-10 inches (70-90% confidence)

As the system passes, NBM shows the following probability`s of gusts
exceeding 45mph from Friday 11PM to Saturday 11PM:

Foothills of the Blues: 50-70%
Columbia Basin: 40-60%
Central OR: 20-40%
Cascades: 50-80%

Although guidance suggests there`s a strong possibility of wind gusts
exceeding 45 mph or greater, confidence is still low to put out a Wind
Advisory for any zones at this point, but additional monitoring is
needed as we get closer to the event for any additional needed products.


Ensemble guidance going through Sunday paints an upper trough with low
pressure setting up offshore of the PacNW moving in the area.
Confidence has not increased from earlier, as clusters seem to not want
to agree on amplitude/timing for this next system heading into Sunday.
Of the clusters, 38% favor a more deeper trough digging off the PacNW,
while a very small sub-set, 9%, favor a weaker trough. Timing is split
among the clusters with 28% want to bring the trough axis sooner than
25% of the members. Regardless of outcome, another round of mountain
snow and low-level rain remain likely (70-90% chance). How much QPF
we receive remains to be determined until clusters can converge on
a solution.

&&

.AVIATION...(Previous Discussion)
06Z TAFs...VFR conditions are will persist through the forecast
period. Winds have upticked just slightly at PSC to 10kts but are
expected to diminish overnight. Otherwise, winds across the
remaining TAF sites will remain calm and mostly from the southwest
overnight before BDN/RDM will see an increase to near 10kts
around 10AM. CIGs will be mainly above 10kft with ALW/DLS lifting
around 18-20Z. Bennese/90

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  57  41  60  38 /   0  40  70  90
ALW  55  42  58  39 /  10  50  80  90
PSC  57  40  61  39 /   0  40  60  80
YKM  53  37  53  34 /  10  40  60  70
HRI  58  40  61  37 /   0  40  70  80
ELN  50  36  50  32 /  10  50  60  70
RDM  58  36  54  29 /   0  30  70  70
LGD  55  38  52  34 /  10  40  80  90
GCD  57  39  52  32 /   0  40  90  90
DLS  55  41  53  37 /  10  60  90  80

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory from 5 PM Wednesday to 11 PM PDT
     Thursday for ORZ509.

WA...None.
&&

$$

SHORT TERM...77
LONG TERM....95
AVIATION...90