970
FXUS66 KPDT 112251
AFDPDT
Area Forecast Discussion
National Weather Service Pendleton OR
251 PM PST Tue Feb 11 2025
.SHORT TERM...Tonight through Thursday...Little to talk about on
satellite this afternoon as mostly clear skies have developed
across the PacNW, showing widespread snow coverage across eastern
OR and portions of southeast WA.
A dry and cold northerly flow aloft as developed behind the exit
of a shortwave trough earlier this morning, which has resulted in
temperatures in the teens and 20s, with a few locations having hit
the 30 degree mark along portions of the Columbia and Yakima
rivers. Tonight, an Arctic airmass will continue to filter into
the region under the northerly flow aloft, and combined with
expected clear skies, will result in the coldest night of the
season. Outside the lowest points of the Columbia Basin, there is
a 75-100% chance of low temperatures less than 10 degrees in the
lower elevations, with a 40-70% chance of below 0 degree
temperatures along the northern Blue mountain foothills, John Day
Basin, and central OR. As for the mountain and intermountain
valleys, these chances are closer to 80-100% chance for low
temperatures to dip below 0 degrees tonight.
The cold temperatures will continue tomorrow afternoon while a
transient upper level ridge slides across the PacNW in the
afternoon and evening. Flow aloft will still allow the arctic
airmass to filter into the region throughout the day, but the tap
will gradually close off overnight as the next system arrives to
the region. This will result in 85-100% chances of high
temperatures remaining below freezing in the afternoon tomorrow.
As for low temperatures Wednesday night, there remains a 60-90%
chance of single digit temperatures along the Blue Mountain
foothills, central OR, Yakima/Kittitas valleys, and the
intermountain valleys. In the lower portions of the Columbia
Basin, there is generally a 90-100% chance that temperatures will
be in the lower teens.
Wednesday night through early Thursday morning, the PacNW will
see a return to active weather with the approach of an occluded
front from the southwest. Surface pressure gradients will tighten
across the Blue Mountains ahead of the frontal passage Wednesday
night and Thursday morning. This will result in breezy to windy
conditions developing along the Blue Mountain foothills, in the
Grande Ronde valley, southern Ochoco- John Day Highlands, and
ridges across the southern Blue mountains. Confidence is mod- high
(65-85%) that gusts along the Base of the northern Blues and
through the southern Grande Ronde valley will be between 45-55mph,
though confidence drops to low-mod(25-50%) in localized gusts
greater than 55mph.
The Occluded front will push north into the upper Columbia Basin
in WA by Thursday afternoon, providing initial snow chances across
the forecast area. Shortwave energy ejecting from an upper trough
offshore will accompany the frontal passage, but will continue to
stream across the PacNW through Thursday night. Overall, there is
mod-high confidence (60-80%) in snow accumulations between 1-2
inches across the lower elevations through Thursday night,
excluding the Kittitas and Yakima valleys. Along the OR Cascade
crest and the higher ridges of the Ochoco-John Day Highlands,
accumulations between 4 to 7 inches are expected, with 2 to 4
inches along the WA Cascade crest, and up to 5 inches in the
northern Blues. At this time, winter highlights have not been
issued, but considering the trough passage Friday, highlights may
be needed in the lower elevations and mountains for the additional
snow accumulations. Lawhorn/82
.LONG TERM...Friday through Tuesday...
Synoptic Overview: Ensemble NWP is in good, though not excellent,
agreement regarding the 500-mb pattern through the forecast
period. Guidance depicts a shortwave trough over the PacNW on
Friday, with lingering snow chances area-wide at all elevations;
highest chances will be for the eastern mountains and Blue Mtn
foothills. Saturday AM, drier weather is forecast as a transient
ridge moves overhead. By Saturday PM, active weather returns with
southwesterly flow aloft ushering in a warmer air mass and rising
snow levels. Another shortwave then likely (80% confidence) rounds
the parent upper low and swings through Sunday through Monday,
switching flow aloft to westerly then northwesterly. Drier weather
returns Tuesday as another ridge of high pressure moves into the
PacNW.
Snow chances: NBM probabilities suggest a low chance (10% or less)
of advisory-level snowfall (2-3") across the lowlands during the 48-
hr period ending Monday morning. The Cascades and northern Blues
have a significantly higher chance of advisory-level (5-6") snow (50-
80%). Plunkett/86
&&
.AVIATION...00Z TAFs...VFR conditions are likely for all sites (70%
chance or greater) through the valid period. Morning stratus at
BDN/RDM has dissipated, and confidence in MVFR or lower CIGs
returning to BDN/RDM this evening and overnight is low (20-40%).
Sustained winds of 10 kts or less are forecast through the period
for all sites. Plunkett/86
&&
.PRELIMINARY POINT TEMPS/POPS...
PDT 1 25 4 27 / 0 0 0 60
ALW 3 23 7 28 / 0 0 0 50
PSC 9 28 8 30 / 0 0 0 50
YKM 7 27 6 26 / 0 0 0 30
HRI 7 28 5 28 / 0 0 0 60
ELN 6 26 5 27 / 0 0 0 30
RDM -7 28 5 33 / 0 0 10 70
LGD -9 20 1 28 / 0 0 0 60
GCD -3 27 3 31 / 0 0 0 90
DLS 12 31 13 29 / 0 0 0 70
&&
.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Cold Weather Advisory until 7 AM PST Thursday for ORZ049-050-502-
503-506-509-511.
WA...Cold Weather Advisory until 7 AM PST Thursday for WAZ030-522.
&&
$$
SHORT TERM...82
LONG TERM....86
AVIATION...86
