A negatively tilted upper-level trough and cold frontal boundary brought periods of heavy snow to the eastern Mountains followed by a period of favorable up-slope flow later on Feb 5th into the 6th once the trough axis passed over the CWA.
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The episode as NWS PDT wrote it up.
A negatively tilted upper-level trough and cold frontal boundary brought periods of heavy snow to the eastern Mountains followed by a period of favorable up-slope flow later on Feb 5th into the 6th once the trough axis passed over the CWA.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Pendleton, OR wrote its last area forecast discussion before the first event at Feb 4, 9:38 PM PST, 5 hours 22 minutes earlier.
Area Forecast Discussion
National Weather Service Pendleton OR
938 PM PST Sat Feb 4 2023
Updated aviation discussion
.UPDATE...Performed some very minor updates to the overnight
forecast adjusting temperatures and pops. Remnants of the warm front
continue lifting north across the forecast area with precipitation
pretty much confined to the Cascades and east slopes. Thus lowered
pops across the eastern portion of the forecast area through this
evening. Also bumped temperatures up a degree of two as we remain
under the warm sector through the night.
.SHORT TERM...Tonight through Monday...Visible satellite imagery
this afternoon is showing widespread cloud cover over the region,
while radar and surface observations showing a light precipitation
shield across the western and central portions of the OR/WA areas.
The light precipitation currently pushing north and east across
the Cascades and east slopes is associated with a weak warm front
that has gradually moved across the PacNW today, which is
associated with an upper trough well to the west of the BC and WA
coastlines.
Tonight and early tomorrow, the offshore upper trough will push a
surface cold front across the PacNW, increasing mountain snow and
lower elevation rain chances from west to east. The cold frontal
boundary will momentarily stall west of the Cascades tonight, then
move across the intermountain PacNW starting early tomorrow,
resulting in the heaviest snow and rain accumulations occurring
west of the Cascade crests. However, mountain snow and lower
elevation rain accumulations will become moderate to heavy as the
upper trough axis pushes onshore and across the region through
tomorrow. All told, snow accumulations of 8 to 14 inches (60-70%
confidence) above 3.5kft can be expected north of the I-84
corridor in the Northern Blues of OR/WA, and generally 6 to 9
inches (60-70% confidence) near and just south of I-84 in the
Northern Blues; 6 to 10 inches (70-90% confidence) above 3.5kft
in the Oregon Cascades; and 4 to 7 inches (70-90% confidence)
above 4kft in the Southern Blues and Ochoco-John Day Highlands. As
for the Washington Cascades, the southerly track of the upper
trough will only result in snow amounts of 2 to 5 inches, with
locally higher amounts near the crest. In the lower elevations,
0.1 to 0.3 inches of rain accumulation can be expected through
Sunday night.
Other than precipitation, breezy west winds are expected to
increase across the region with the cold frontal passage. These
winds are expected to increase through the day tomorrow, with
winds peaking in the evening and overnight Sunday in the lower
elevations. Wind gusts will generally be 25-40 mph across the
region, however wind gusts up to 50mph will be possible along the
foothills of the Blue mountains in Oregon. Breezy winds in the
mountains in combination with expected snowfall will also result
in reduction of visibility due to blowing snow, especially in
the northern Blue mountains.
The upper trough will exit into the northern Rockies overnight
tomorrow, allowing ridging in the eastern Pacific to build across
the PacNW. This will result in precipitation chances retreating
to the mountain zones overnight Sunday, then diminishing
everywhere but the WA Cascades Monday morning. Light snow will
still be possible in an upslope northwest to westerly flow, with
additional snow accumulations up to 2 inches. West to southwest
winds will remian breezy to locally breezy across the region
Monday as surface pressure gradients gradually weaken behind the
trough/cold front exit.
Temperatures over the next several days will be near to above
normal for the lower elevations, and near to below normal in the
mountain zones. In the lower elevations, afternoon highs will be
in the 40s to lower 50s...30s in the mountains. Lawhorn/82
.LONG TERM...Tuesday through Saturday...The extended period begins
under the influence of a progressive and active weather pattern
however conditions quickly trend much calmer and drier for the
latter half of the week. Impacts revolve around mountain snowfall in
the Cascades and to a some extent the Northern Blue/Wallowa
Mountains through Wednesday morning, in addition to breezy
conditions throughout the Columbia Basin Tuesday afternoon/evening
as well. Fortunately, conditions remain within climatological norms
as depicted by the ECMWF Extreme Forecast Index going forward.
Both deterministic and ensemble guidance are in good agreement
regarding the evolution of the large-scale pattern to begin the long
term period as a low amplitude shortwave trough traverses into the
Pacific Northwest Tuesday. This shortwave feature is preceded by a
warm-frontal boundary likely increasing precipitation over higher
elevation areas the first half of the day, especially in the
Cascades, quickly followed the more potent shortwave axis and
accompanying cold front swinging through the CWA during the
afternoon and evening. As previously mentioned, mountain snowfall is
the primary impact associated with this disturbance. The NBM
projects a 55-80% probability of exceedance for 6in of snow over the
Washington Cascades with lower probabilities comparatively for the
Oregon Cascades and Blue Mountains; highest impacts for the former
area. Expect breezy conditions for much of the region later Tuesday
into Wednesday as well, although currently winds don’t appear
particularly strong or abnormal. Still, we’ll have to keep an eye on
a 40-50 knot 850mb jet show by most deterministic guidance as the
forcing provided by the passage of the cold frontal boundary could
mix these stronger winds closer the surface. Forecasted winds were
generally in-line with the model consensus of widespread 25-35 mph
gusts as the scenario involving strong winds mixing down from aloft
isn't yet favored by ensemble or deterministic models; something to
watch in the coming days.
Confidence is high(70-90%) the shortwave trough quickly exits the
region to the east Wednesday morning followed by building heights
and a shift to northwesterly flow the remainder of the day. The post-
frontal conditions in place favor lingering shower activity over the
higher terrain areas, then the increasing influence of a ridge of
high pressure directly to our west and the loss of daytime heating
lead to the return of dry conditions Wednesday evening/night. Moving
forward, deterministic and ensemble guidance shift the ridge of high
pressure overhead on Thursday and Friday; calm and dry weather
prevails. While this is the general trend, ensembles point to some
uncertainty regarding the amplitude and progression of the ridge
Thursday onward, particularly as an upper-level trough over the
eastern Pacific transitions to a closed low, diving southward off
the California coastline Friday and Saturday. Exploring the Ensemble
Cluster Analysis reveals nearly 36% of the Grand Ensemble
members(heavily comprised of GEFS members) favors a weaker ridge,
shifting it far enough to our east by Friday for light snow showers
to return to the Cascades. The other 64% of ensemble members and the
deterministic GFS/ECMWF still favor a stronger ridge and drier
solution by comparison. Discrepancies in the upper-level pattern
increase further Saturday but 68% of ensemble members hold onto dry
weather locally. Due to the cold frontal passage later Tuesday
ushering in a cooler airmass followed by the quick arrival of the
ridge of high pressure, temperatures trend roughly 3-8 degrees below
normal the Wednesday through remainder of the week; most pronounced
during the overnight hours and over the higher elevations.
Schuldt/99
&&
.AVIATION...06Z TAFs...Generally VFR conditions but with
brief MVFR due to -SHRA or -RA overnight through Sunday. Conditions
improve Sunday as winds increase and precipitation decreases in the
afternoon to evening period. Winds will be 5-15 kts overnight and
then expect increase on Sunday for all sites except YKM to 10-20kts
and higher gusts, especially PDT.
&&
.PRELIMINARY POINT TEMPS/POPS...
PDT 38 49 34 49 / 60 80 30 0
ALW 38 48 33 51 / 50 80 40 10
PSC 35 47 35 50 / 40 70 10 0
YKM 33 47 29 48 / 50 50 0 0
HRI 35 49 35 51 / 60 70 10 0
ELN 33 42 32 43 / 60 40 10 10
RDM 36 47 27 46 / 60 40 10 0
LGD 34 43 30 42 / 60 80 50 10
GCD 36 44 27 41 / 70 70 30 10
DLS 37 49 38 49 / 60 70 10 10
&&
.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Winter Storm Warning from 4 AM Sunday to 4 AM PST Monday for
ORZ502.
Winter Weather Advisory from 4 AM Sunday to 4 AM PST Monday for
ORZ503-506-509.
Wind Advisory from 4 PM Sunday to 7 AM PST Monday for ORZ507-508.
WA...Winter Storm Warning from 4 AM Sunday to 4 AM PST Monday for
WAZ030.
&&
SHORT TERM...82
LONG TERM....99
AVIATION...99The national radar mosaic for the moment the first event began.
2 heavy snow. Local standard time, as filed.
The SNOTEL site COLO3(County Line) recorded 9 inches over a 13 hour period ending at 0100 on Feb 6th, and the SNOTEL site GLDO3(Gold Center) recorded 7 inches in a 16 hour period ending 0100 Feb 6th.
The SNOTEL site MLKO3(Milk Shakes) recorded 17 inches over a 19 hour period ending at 0100 on Feb 6th, and the SNOTEL site HIRO3(High Ridge) recorded 14 inches also in a 19 hour period ending 0100 Feb 6th.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Oregon in 2023Every state in 2023This day in weather historyWarnings in Oregon, February 2023
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 1083537, 1083536.