952
FXUS66 KPDT 080057
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
457 PM PST Fri Feb 7 2025

.AFTERNOON UPDATE...A mid-level shortwave embedded within a
broader upper-level trough is passing over eastern Oregon and
southeast Washington this afternoon. Coupled with orographic
lift, this shortwave is likely responsible for the lingering
snowfall across the region this afternoon. With regard to
highlights, opted to allow the Winter Storm Warnings for the OR
Blue Mountain foothills to expire as the region is now behind the
shortwave, and thus snowfall is tapering off; likewise, let the
Winter Weather Advisory for the WA Blue Mountain foothills expire
for the same reasons. Elsewhere, extended the Winter Weather
Advisories for the northern and southern Blue Mountains, the
Grande Ronde Valley, and Wallowa County until 7PM PST. Thinking is
we will see up to an inch of additional snowfall, locally higher,
before the shortwave exits into Idaho and snow tapers off through
this evening. Plunkett/86

&&

.PREV DISCUSSION... /issued 204 PM PST Fri Feb 7 2025/

SHORT TERM...Today through Sunday...The axis of a broad trough
remains centered over the forecast area this afternoon, resulting
in a band of light snow that has lingered around the Basin and
foothills of the Blues for much of the day today. Latest radar
imagery suggests that this band of snow is finally shifting
eastward into the Blues and Wallowas, with dry conditions expected
to prevail later this evening as drier, colder air circulates
behind the trough axis. The remaining Winter Weather Headlines are
set to expire at 4 PM this afternoon, and with the majority of
snow accumulation winding down, don`t see a reason to extend
current headlines at this time.

Looking ahead, the next best chance for precip over the weekend
looks to be during the Saturday evening into early Sunday morning
period, as a cold front treks across the PacNW. With how cold the
air mass is behind the front, moisture will be lacking, however
the approach of the front does favor upslope enhancement across
the northern Blues. Guidance currently calls for 6 to 8 inches, so
advisories will likely be needed, but will hold off on any
issuance for now given the current headlines in effect. Could see
moderate accumulations along Santiam Pass in the 3 to 6 inch
range, with a couple of inches at Snoqualmie Pass, but am not
anticipating headlines for the Cascades at this time. Lowland snow
will be limited, but the foothills of the northern Blues could
see some light upslope snow during this time period up to an inch.
Confidence is on the lower end of this occurring, however (40%
chance over an inch), given the dry nature of the oncoming
airmass.

Sunday onward, cold temperatures will become the next focus in the
forecast. The region will find itself under a period of northerly
flow aloft, which will allow for an outbreak of Arctic air. The
coldest temperatures are not anticipated to occur until midweek,
but expect overnight lows to start ticking down into the teens and
single digits by Sunday night into Monday morning. Evans/74

&&

.LONG TERM...Monday through Friday...Sensible weather concerns
through the extended will center around a modified arctic airmass
producing potentially dangerous cold temperatures across the
region through Thursday morning, followed by a return to active
weather towards the end of the work week.

The ensemble mean guidance from the GFS and ECMWF start in good
agreement Monday in a dry shortwave trough with accompanying
back-door cold front dropping through British Columbia and into
the PacNW, with flow becoming northerly behind the trough
axis/cold front boundary. By Tuesday, ensemble mean guidance
begins to differ in exit timing of the shortwave trough to our
south, however, the discrepancies in impacts between the two are
very low. A transient ridge will slide across PacNW Wednesday from
the west, with flow aloft becoming zonal briefly late Wednesday.
Monday through Wednesday, precipitation chances will be fairly low
(<30%) as the incoming systems will have very little
precipitation to work with. During this three day period, there
will be a 25-50% chance of 1 inch of snow in the Blues, and a
60-80% chance of 1 inch of snow along the OR Cascades. Outside of
these areas, chances of any accumulating snow will be less than
25% through the three day period. While precipitation will not be
a concern, the attention will turn to daily very cold temperatures
region wide. Across the lower elevations and mountain area, there
is high confidence (75-90%) in widespread morning low
temperatures in the single digits to teens Tuesday morning, mod-
high confidence (60-80%) in widespread single digits Wednesday
morning. In fact, there is a 70-90% chance that temperatures
across the high and inter-mountain valleys will drop below 0
degrees in Oregon Wednesday morning. While still a ways out, cold
weather advisories may be needed, as even weak winds could lead to
wind chills dropping below -10 degrees.

Thursday into Friday, there is good agreement from ensemble
guidance in an upper trough sliding across the PacNW, resulting in
increasing precipitation chances area-wide. While there will be
some warming across the region Wednesday night into Thursday
morning, snow levels will still be at or below the surface area-
wide, resulting in mostly snow chances across the forecast area
(confidence 50-70%), with low confidence (20-25%) in exact amounts
of snow accumulations at this time. That said, there is at least
moderate confidence (60%) in the lower elevations seeing light
snow with moderate snow accumulations in the mountains. Lawhorn/82

&&

.AVIATION...00Z TAFs...MVFR or less conditions will prevail
through early afternoon at sites PDT/YKM/ALW/PSC, with VFR
conditions at all other sites and through the period. Light snow
has been slow to move out of the region this afternoon, which has
resulted in continued impacts at sites PDT/ALW/PSC, but the band
is expected to move out before sunset at the latest. After this
band moves out, the expectation is that these sites will improve
to VFR into the early evening hours. After that, VFR conditions
will prevail into tomorrow morning at all sites. Tomorrow morning,
another weather system will move into the region, bringing
another round of periodic light snow to sites DLS/RDM/BDN between
13Z to 17Z (confidence 40-50%). Winds will be light, less than
12kts, through the period. Lawhorn/82

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  18  37  23  34 /  10  30  50  20
ALW  21  38  24  35 /   0  40  60  30
PSC  23  38  24  38 /   0  20  20  10
YKM  19  37  18  38 /  10  10  10   0
HRI  23  39  24  38 /  10  20  30  10
ELN  18  35  17  35 /  10  20  10   0
RDM  14  38  15  34 /  10  20  10   0
LGD  15  33  21  34 /  20  30  70  30
GCD  11  34  19  34 /  10  30  30   0
DLS  26  42  25  42 /  20  60  10  10

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 7 PM PST this evening for ORZ049-
     050-502-503.

WA...Winter Weather Advisory until 7 PM PST this evening for WAZ030.

&&

$$

AFTERNOON UPDATE...86
SHORT TERM...74
LONG TERM....82
AVIATION...82