An upper level trough coupled with surface cold front passing over the region from Dec. 22nd through early Dec.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS PDT wrote it up.
An upper level trough coupled with surface cold front passing over the region from Dec. 22nd through early Dec. 24th brought moderate snow showers across mountain areas in Northeast Oregon and Southeast Washington.
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 Dec 22, 3:41 AM PST, 19 minutes earlier.
Area Forecast Discussion
National Weather Service Pendleton OR
341 AM PST Wed Dec 22 2021
.Updated for Aviation...
SHORT TERM...Wednesday through Friday...Forecast area remains
under an area of enhanced SW flow as a result of a low pressure
system dropping in from the Gulf of Alaska and absorbing a cutoff
low centered off the California coast. As a result, orographic
snow showers will be possible across our mountain zones through
much of the day Wednesday. The overall synoptic pattern favors
persistent chances for mountain snow through much of the short
term and even beyond, but looks like the period of most enhanced
moisture transport will be Wednesday afternoon through the
overnight hours into Thursday morning. Winter storm warnings
remain in effect for our Cascade zones, with a winter weather
advisory issued for the northern Blues of WA, as model QPFs have
favored a period of moderate to heavy snowfall more towards late
Wednesday night into early Thursday morning. Right now, looking
like OR Cascades will have a better shot at meeting warning
criteria for snowfall compared to the WA Cascades. Not expecting
as much impactful snow for the major mountain passes around the
Blues, but those traveling for the holidays should prepare for
difficult driving conditions nonetheless.
By Thursday into Friday, another trough dropping in from the Gulf of
Alaska will work to amplify the synoptic pattern and create
substantial ridging over Alaska and broad troughing over the PacNW.
The net effect will be a trend towards cold temperatures heading
into Christmas weekend. Thursday looks to be a bit breezy to windy,
especially around the foothills of the Blues and Grande Ronde
Valley, as the front associated with Wednesday's system passes
through, before broad troughing works to cycle several weak systems
into our area. Precip will be limited mainly to our mountain zones,
while temperatures begin to slide towards unseasonably cold beyond
the short term. Snow levels will be below 1500-2000 ft across the
entire forecast area by the end of the week. While only a couple
stray showers are possible across the lower elevations and valleys,
travel may become challenging across mountain passes for the
holidays as the overall pattern supports persistent snow chances for
both the Cascades and Blues. 74
LONG TERM...Saturday through Wednesday...Several troughs will move onshore
during the extended period. The first will be during the day
Saturday. The next one will follow on its heels on Sunday. A
stronger, deeper trough will then move through on Monday. All of
these systems will bring mainly light snow to the mountains, with the
one on Sunday and Monday possibly bringing some light snow to the
portions of the lower elevations as well. Monday may also be a bit
breezy as the trough moves through.
However, the big story will be the much colder temperatures, by the
end of the period. Highs Christmas Day will mainly be in the 30s
and 40s across the Columbia Basin and Blue Mountain Foothills.
Temperatures will drop each day and by Monday Highs will struggle to
reach freezing in most areas and by Tuesday most locations will be
in the low to mid 20s, with central Oregon, possibly making it to 30
degrees. It gets even colder through midweek. Overnight lows start
in the 20s and 30s, and bottom out in the single digits.
The ECMWF Extreme Forecast Index (EFI) approaches 80-90% for both
high temperature mainly in central Oregon from on Monday, and is 70-
80% Sunday through Wednesday. All of the ensemble clusters are in
good agreement that there will be well below normal 500 mb heights
over the west from Saturday through Monday. Beyond Monday, the
height patterns and anomalies begin to differ as there is some
disagreement in the exact location of the axis lowest heights.
However, all guidance does agree that the midweek period will be
very cold.
AVIATION...
12Z TAFS...Most TAFS are VFR early this morning. The exception is
YKM that remains IFR and had been as low as LIFR earlier. DLS has
been fluctuating between MVFR and VFR. Localized MVFR or lower
can not be ruled out through the morning hours. However, as the
next area of moisture moves onshore later this afternoon into the
evening, more lowered conditions are expected, especially for
DLS/BDN/RDM in -RA. MVFR is expected, and some local IFR can not
be ruled out. MVFR is also forecast at PDT and ALW though
confidence is lower and chances of -RA are less as well. Some
local IFR is also possible at these locations.
&&
.PRELIMINARY POINT TEMPS/POPS...
PDT 45 36 45 31 / 10 40 50 20
ALW 43 38 45 33 / 10 50 60 30
PSC 44 37 46 35 / 20 30 10 10
YKM 40 30 43 26 / 30 60 40 30
HRI 44 36 47 33 / 10 40 30 10
ELN 36 28 37 23 / 30 60 40 40
RDM 47 33 42 27 / 20 60 60 30
LGD 38 33 39 26 / 10 60 70 50
GCD 42 36 41 26 / 10 60 60 40
DLS 42 36 43 33 / 70 90 90 70
&&
.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Winter Storm Warning from 10 AM this morning to 4 PM PST
Thursday for ORZ509.
WA...Winter Weather Advisory from 4 PM this afternoon to 4 PM PST
Thursday for WAZ030.
Winter Storm Warning until 10 AM PST Thursday for WAZ520.
&&
SHORT TERM...74
LONG TERM....77
AVIATION...77PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PENDLETON OR
1057 PM PST TUE DEC 21 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1053 PM FREEZING RAIN 2 WSW FRUITVALE 46.61N 120.58W
12/21/2021 E0.25 INCH YAKIMA WA TRAINED SPOTTER
SPOTTER WAS UNSURE OF EXACT AMOUNT OF ICE,
SO LIKELY AN OVERESTIMATE. OBSERVATIONS IN
AREA AROUND .01 INCH. STATION ELEVATION:
1353 FT.
&&
MC1 heavy snow. Local standard time, as filed.
A trained spotter in Easton, WA estimated 36 inches of snow accumulated in a 2 to 3 day period.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Washington in 2021Every state in 2021This day in weather historyWarnings in Washington, December 2021
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: 1004291.