A trough and strong cold frontal boundary moved through the region late on the 25th followed by a frequent post-frontal snow showers on the 26th. Enhanced shower banding over the Oregon Cascades due to modest westerly flow and cold air aloft lead to locally higher accumulations.
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The episode as NWS PDT wrote it up.
A trough and strong cold frontal boundary moved through the region late on the 25th followed by a frequent post-frontal snow showers on the 26th. Enhanced shower banding over the Oregon Cascades due to modest westerly flow and cold air aloft lead to locally higher accumulations.
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 24, 8:31 PM PST, 3 hours 29 minutes earlier.
Area Forecast Discussion
National Weather Service Pendleton OR
831 PM PST Fri Feb 24 2023
.EVENING UPDATE...The forecast remains on track tonight as calm
and dry conditions prevail going forward through the day Saturday.
Primary impacts over the 12-18 hours revolve around near record
breaking low temperatures expected for much the region come
sunrise Saturday morning. With this in mind, temperatures so far
this evening have been decreasing slightly quicker than
anticipated, especially around central Oregon and in many of the
mountain valley locations, likely due to clear skies, light winds,
and snow-cover facilitating very efficient radiative cooling and
boundary layer decoupling. Low temperatures were adjusted to match
this trend. Otherwise, the focus shifts to an upper-trough moving
into the Pacific Northwest Saturday night and Sunday bringing
another round of snowfall impacts, primarily to the mountain
areas. Schuldt/99
.PREV DISCUSSION... /issued 223 PM PST Fri Feb 24 2023/
SHORT TERM...Tonight through Sunday night...Deterministic and
ensemble models are in very good agreement that an upper low
pressure system will break off from the main upper trough and sag
southward to the central CA coast by 12Z Saturday. This will
place the forecast area in between that upper low and a weak
upper trough over northeast WA to northwest MT. This will result
in dry conditions through Saturday.
The flow aloft will then become southwesterly as the next Pacific
upper trough moves into the region Saturday night and Sunday.
This southwest flow will result in warm air advection, bringing
warmer temperatures, and increasing snow levels. Snow levels will
rise to about 2000 ft over the southern WA Cascades and to around
4000-4500 feet over the northern OR Cascades by 12Z Sunday. After
that, the upper trough axis will move across the CWA, with snow
levels lowering again behind the trough axis. This scenario will
bring snow to the Cascades beginning Saturday night and Sunday.
Though the snow may turn to rain for a brief time ahead of the
trough axis over the northern OR Cascades, precipitation will
change back to all snow by 06Z Sunday. Snow will then continue
over the Cascades of both OR and WA through early Sunday evening.
Storm total snow amounts will reach Winter Weather Advisory for
both the OR and WA Cascades late Saturday night through Sunday
evening. As such, will issue a Winter Weather Advisory from 06Z
Sunday (10 PM PST Saturday) through 06Z Monday (10 PM PST Sunday).
Confidence is moderate to high (60-80 percent). NBM 4.1 WSUP is
showing a high probability of up to 80-90 percent of greater than
6 inches of snow over the Cascades of both OR and WA. It is
showing mostly up to a 50-70 percent chance of greater than 8
inches, mainly over the highest peaks of the Cascades, including
Snoqualmie Pass and the OR passes. With the lower probabilities
for greater than 8 inches, will go with an advisory rather than a
Winter Storm Watch.
Over the northern Blue Mountains, storm total snow amounts will be
up to 3-5 inches over Deadman Pass (the I-84 corridor), and up to
6-9 inches over the highest peaks/ridges of the northern Blues.
Due to the fact that the I-84 corridor is only expected to receive
3-5 inches, will hold off on issuing any highlights for the
northern Blues at this time, and will let later shifts re-analyze
the situation. In addition, the NBM 4.1 WSUP is only showing a
30-40 percent chance of receiving greater than 6 inches, and
advisory criteria is 6-10 inches.
Elsewhere, there will be light amounts of snow of mostly 2-5
inches over the southern Blue Mountains, the Ochco-John Day
Highlands, and the Simcoe Highlands. There will be mainly less
than an inch where snow levels will be low enough for snow at the
surface. Elevations below those levels will have mainly rain, or
possibly rain mixed with snow at night.
Another concern during the short term period will be increasing
winds in the Grande Ronde Valley by late Saturday morning. These
winds are expected to remain below advisory criteria. Then by
early Sunday morning, after the upper trough passage, southwest to
west winds will increase area-wide over the CWA. This will be
especially the case from the Blue Mountains northward and
westward, including north central OR. However, wind speeds will
be just shy of advisory criteria, and it will need to be
monitored closely in case forecast guidance and probabilities
trend upward in wind speeds.
Temperatures will be on a slow warming trend, after another very
cold night tonight. Currently, there is persistent a low stratus
deck that stretches from north central OR northeast to the
Foothills of the Northern Blue Mountains. These clouds are
expected to dissipate by this evening. As a result, there will be
strong radiational cooling, especially over areas that are snow
covered. Elsewhere skies will be mostly clear tonight, also with
strong radiational cooling. Lows are expected to range from the
single digits to lower teens in central OR, and mostly in the
teens elsewhere. Then on Saturday, highs will increase to mostly
the 30s in the lower elevations, where inversions will exist...to
the upper 30s to mid 40s elsewhere. Then on Sunday, the lower
elevations will warm up to the 40s as the winds mix out the
inversions. Temperatures elsewhere will generally decrease to
mostly the mid 30s to lower 40s...with some upper 20s to lower 30s
over the higher mountain peaks and ridges. A warming trend will
then continue into the extended forecast period with another
Pacific weather system moving into the region on Monday. 88
LONG TERM...Monday through Friday...Confidence is high that an
active weather pattern will continue through next week with periods
of mountain snow and widespread breezy to windy conditions, though
as is typical with longer lead times, details on timing and
magnitude are unclear.
Ensemble guidance is in excellent agreement that another offshore
low pressure system will move into the Pacific Northwest on Monday
and linger through at least Tuesday night. This will bring
widespread precipitation chances to the mountains and lower
elevations with light to moderate mountain snow currently expected.
Light lowland snow is also forecast with the exception of the lowest
elevations of the Columbia Basin. The ECMWF EFI is highlighting
climatologically unusual winds through the Grande Ronde Valley and
across portions of central Oregon and the Blue Mountain foothills,
though confidence is highest in wind highlights for the Grande Ronde
Valley.
Ensemble cluster analysis reveals significant timing differences
with regard to the speed with which the trough exits the forecast
area. Guidance is roughly split between having it linger through
Wednesday night or having it exit Tuesday night. Thus, confidence
in timing is low. Ensemble and deterministic guidance then favor a
brief reprieve from precipitation either Wednesday or Thursday
depending on when the first trough exits.
More uncertainty develops with regard to subsequent troughing
advertised in ensemble means and current 12Z deterministic runs.
Generally speaking, zonal flow develops Thursday with a quick-
hitting shortwave traversing the region Thursday afternoon or
Friday. Given the increased winds aloft, this pattern will support
breezy to windy west winds across the forecast area (again
highlighted by the ECMWF EFI) and bring precipitation chances back
to the forecast. Plunkett/86
&&
.AVIATION...06Z TAFs...VFR conditions are generally expected to
persist through the TAF period. However, we’ll still need to be on
the lookout for potential localized low cloud/freezing fog
formation later overnight at KALW, KRDM, KBDN, and to some extent
KPDT as the set-up of light winds, clear skies, surface inversion, and
snow-cover could be conducive to its formation. However, current
high resolution guidance favors the continuation of VFR
conditions; the most likely outcome and what's reflected in the
TAFs. Winds remain light, generally less than 10 knots at all
sites. 99
&&
.PRELIMINARY POINT TEMPS/POPS...
PDT 5 35 22 41 / 0 0 10 80
ALW 7 36 24 43 / 0 0 10 90
PSC 15 36 25 48 / 0 0 10 30
YKM 9 36 23 45 / 0 0 20 10
HRI 9 36 23 46 / 0 0 10 40
ELN 8 35 24 41 / 0 0 30 10
RDM 1 46 24 38 / 0 0 10 40
LGD 18 43 29 38 / 0 0 10 100
GCD 13 45 25 38 / 0 0 10 80
DLS 13 40 29 44 / 0 0 30 70
&&
.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory from 10 PM Saturday to 10 PM PST Sunday
for ORZ509.
WA...Winter Weather Advisory from 10 PM Saturday to 10 PM PST Sunday
for WAZ520.
&&
UPDATE...99
SHORT TERM...88
LONG TERM....86
AVIATION...99The national radar mosaic for the moment the first event began.
1 heavy snow. Local standard time, as filed.
The SNOTEL site HOPO3(Hogg Pass) recorded 11 inches over a 19 hour period ending at 2100 on Feb 26th.
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: 1083609.