126
FXUS66 KPDT 221035
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
235 AM PST Fri Nov 22 2024

.SHORT TERM...Today through Sunday...A closed upper level low
pressure system continues off the coast with several shortwaves
rotating around it. One is currently moving north off the coast and
lifting a warm moist airmass across the forecast area in the from of
a warm front. Snow levels will be 5000 to 7000 feet through the
morning meaning rain in most of the forecast area and snow only in
the highest elevations. The warm front will lift north of the
forecast area by midday pushing most of the rain north of the
forecast area. Then a cold front will begin to push west to east
across the forecast area this afternoon and overnight accompanied by
a slow moving band of precipitation that moves off into Idaho on
Saturday. With it we will see a lowering of snow levels 3000 to 4500
feet by Saturday morning with a return of some snow in the higher
terrain and mountains. The low pressure system remains off the coast
on Saturday which keeps a moist southwest flow across the forecast
area and mainly some mountain showers. Overall, snow amounts look to
remain below advisory levels for the mountains during this
event but passes will see some snow accumulations.

The low pressure consolidates into a smaller low off the coast
Saturday night through Sunday while still keeping the forecast area
under a southwest flow and with snow levels 2500 to 3500 feet. This
will lead to some continued showers over some of the forecast area
but with lite precipitation amounts.

Winds will continue to be an issue along the base of the Blue
Mountain Foothills and the southern Grande Ronde Valley until the
cold front passes through the area this afternoon. The wind
advisories will continue for these areas at least until the late
afternoon.


.LONG TERM...Monday through Friday...A colder and drier pattern is
in store for the forecast area for Thanksgiving week, as ensembles
broadly favor a transition from broad troughing towards that of dry
northerly flow by the end of next week. Best chances for precip
would be across the high mountains, but even with snow levels
lowering, QPF across ensemble guidance is unimpressive, reflecting
the drier air mass moving in under the expected synoptic pattern
change.

Not much disagreement to start off the period as ensemble consensus
points toward the broad, offshore low that has been plaguing the
forecast area with windy and wet conditions for the past week
finally moving onshore by late Monday. Colder air starts to move in
as a result, and the instability provided by the low`s center will
support broad PoPs (30-40% valleys, 60-70% mountains) across the
area, with snow levels around 3000-4000 feet, but with meager QPF as
this low lacks a sufficient moisture advection mechanism. This low
moves out of the PacNW by late Tuesday, leaving us with dry and cold
northerly flow in its wake. High temps will struggle to climb out of
the mid 40s, and we certainly can`t rule out pockets of Basin fog,
given the relatively saturated airmass and benign wind pattern,
however confidence is too low (<20%) to mention the possibility
directly in the forecast.

PoPs gradually scale back for the remainder of the period. A slight
chance (15-25%) of PoPs persists across the high mountains in the
wake of upslope, northerly flow, but as of now, confidence is
moderate to high (60-70%) that the area will not see a significant
precip event that would otherwise impact Thanksgiving travels, at
least through Wednesday and Thursday. Models split by the tail end
of the period, with the EPS broadly favoring a persistent north to
northwesterly flow solution, perhaps with an embedded shortwave,
while the GEFS suggests ridging may move in after Thanksgiving.
Forecast confidence beyond Thanksgiving day is low, however (<30%).
Evans/74

&&

.AVIATION...12z TAFs...Variable conditions expected this morning as
low cigs and fog impact many sites in the Basin, complicated by
oncoming rain and wind expected through the late morning.
Expectation is that fog will lift as rain moves in, with sites such
as PDT and ALW still seeing IFR or worse conditions due to low cigs,
with all sites seeing VFR by the late afternoon/early evening as
conditions dry and winds in PDT/ALW mix out fog. Another round of
rain is then expected around nightfall Friday night, impacting most
sites, save DLS and YKM, with at least MVFR conditions. Evans/74



&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  59  40  48  34 /  80  90  60  20
ALW  58  40  49  36 /  90 100  80  20
PSC  51  42  51  38 / 100  80  30  20
YKM  47  31  47  31 / 100  20  10  20
HRI  53  41  51  35 / 100  90  40  20
ELN  46  30  45  30 / 100  20  10  20
RDM  55  34  44  30 /  60  50  20  10
LGD  48  37  44  29 / 100 100  90  20
GCD  53  37  44  25 /  80 100  80  20
DLS  53  40  52  37 / 100  30  20  30

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory until 3 PM PST this afternoon for ORZ049-507.

WA...Wind Advisory until 3 PM PST this afternoon for WAZ029.

&&

$$

SHORT TERM...91
LONG TERM....74
AVIATION...74