116
FXUS66 KPDT 230547
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
947 PM PST Sat Feb 22 2025


&&

.AVIATION UPDATE...06z TAFs...Rain and gusty winds prevail through
the area as the atmospheric river passes through and the warm
front advances past the area. Radar indicates at the beginning of
the period a break in the precip. Most sites will see another
round of precip by 09Z as the cold front advances into the region.
Winds continue to be gusty, with some sites gusts up to 30 knots,
with DLS and PSC peaking lower around 10-15 knots. Conditions
will be MVFR at times with the heaviest of rain, but CIGs are
expected to remain elevated due to the stronger winds to prevent
IFR conditions a possibility. LLWS is included for PDT/RDN/BDN as
winds continue to stay strong.


&&

.PREV DISCUSSION... /issued 820 PM PST Sat Feb 22 2025/

SHORT TERM...Today through Monday...

Bottom Line Up Front

1) Moderate mountain rain/snow, light lowland rain to start

2) Breezy to windy conditions through Sunday night

3) Hydrological concerns Monday

Current satellite shows high clouds across the area as the upper
level trough begins to push onshore. Current radar is showing the
warm front has begun to move across the area bringing light rainfall
to the WA Cascade crests. Temperatures along the foothills of the
northern Blues have risen above 60s with the downsloping off of the
Blues.

Sunday through Monday night, models show a wet upper level low
coupled with a strong atmospheric river making its way across the
region exiting by Monday night. Both the GFS and ECMWF IVT ensemble
suites show close to a 100% chance of IVT values greater than 250
kg/m/s making it east of the Cascade crest. This will allow for
relatively moderate rainfall accumulations along the mountains, with
locally moderate rainfall across the lower elevations. The NBM 48-hr
probabilities ending Monday morning for precipitation accumulations
show 95-100% probabilities along the Cascade crest and east slopes
with 70-90% probabilities along the northern Blues for 1 inch of
rain. At 2 inches or higher, probabilities are 70-90% along the
Cascade crest and 35-55% probabilities along the higher terrain of
the northern Blues. Snow levels will be relatively high to begin
with Sunday through Monday afternoon before steadily decreasing with
the models showing the snow levels nearing 4500 feet. Models show
there is snow expected to fall above 4500 feet Monday night with the
highest amounts along the higher crests. 60-80% of the raw ensembles
show there to be between 0.01-0.04 inches along the crests of the
eastern mountains and northern Blues.

Breezy conditions will accompany the system this afternoon ahead of
the shortwave trough and warm front. Model guidance shows surface
pressure gradients across the Northern Blue Mountains of OR will
increase to around 10-12mb this evening and overnight bringing the
strongest winds (gusts between 40-50mph) through the Grande Ronde
valley and along the Blue Mountain foothills of OR and WA as well as
later into central and north central OR through Sunday afternoon and
lingering through Sunday night with high confidence of 70-90%. Wind
advisories will begin for all areas mentioned at 4 PM and remain in
affect through 10 PM Sunday. As for central and north central OR,
the wind advisory will begin at 4 PM Sunday and continue until 10
PM.

Lastly and most importantly, there are some hydrological concerns
that are popping up from all the warm temperatures and
precipitation. Rivers through the Yakima, Naches, Klickitat, Walla
Walla and the lower Yakima River Basins will see rises. The Naches
at Cliffdell is forecast to break above bankfull by Monday with
probabilities of 10-25%, Walla Walla River near Touchet with
probabilities of 25-75% breaching action stage and Klickitat River
near Pitt 10-25% reaching action stage as well. A hydrologic outlook
has been issued and we will continue to closely monitor the river
forecasts and work with the river centers as the day draws closer.
In the meantime, be prepared and continue to remain vigilant and
check the website for updated information regarding the rivers.
Bennese/90

LONG TERM...Tuesday through Saturday...Ensemble consensus points
toward that of a more benign, spring-like pattern for next week,
with only limited chances for precip through the work week and temps
in the lower elevations wavering around the upper 50s and low 60s.
These generally quiet conditions will lead to chilly overnights with
lows in the 30s, but temps overall will run 5-10 degrees above
average - a nice break from what has otherwise been a cold and snowy
February.

The last of the oncoming atmospheric river is expected to move out
by early Tuesday morning. Light, lingering mountain precip may last
through the morning (PoPs generally 30-50%), before dry conditions
prevail in the afternoon as ridging starts to build in. Ensemble
clustering shows little break in this ridging through the work week,
with deterministic guidance showing potentially a weak upper-level
wave to our north briefly flattening the ridge, but still leaving us
under benign zonal flow. Nothing to note synoptically until the
weekend, when guidance tries to bring in a trough late Saturday into
Sunday. GFS and ECMWF show a good amount of unity between each other
on the upper-level pattern through the week, while clusters show
solutions falling out of sync by the start of next weekend. Majority
of guidance does depict a system arriving next weekend, but until
then, PoPs will be limited to the high mountains, with little if any
precip expected to occur. Overall forecast confidence falls around
60-70%, with only complicating factor being the potential impacts of
next weekend`s system. Evans/74


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  47  65  41  61 /  60  90  70  70
ALW  45  62  41  57 /  80 100  90  70
PSC  44  66  38  57 /  80  70  50  60
YKM  40  61  33  49 /  60  80  50  80
HRI  45  60  39  61 /  60  70  50  70
ELN  38  54  33  46 /  80  80  60  80
RDM  43  63  37  59 /  60  70  50  60
LGD  37  50  35  48 /  90 100  90  70
GCD  40  55  37  53 /  90  90  60  70
DLS  46  61  41  55 /  80  90  70  90

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory until 10 PM PST Sunday for ORZ049-507-508.

     Wind Advisory from 4 PM to 10 PM PST Sunday for ORZ510-511.

WA...None.
&&

$$

SHORT TERM...90
LONG TERM....74
AVIATION...95