An upper level weather system pushed a cold front into the Pacific Northwest late Dec. 18th, where the frontal boundary had stalled across southeast Washington and northeast Oregon through Dec.
Every event with a place to put it; 6 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.
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 weather system pushed a cold front into the Pacific Northwest late Dec. 18th, where the frontal boundary had stalled across southeast Washington and northeast Oregon through Dec. 20th where the stationary frontal boundary had weakened in the afternoon. As a result, bands of rain, freezing rain, and snow were produced across portions of the forecast area during the 19th and 20th, with snow being reported across the lower elevations in the Columbia Basin and mountain locations across southeast Washington and northeast Oregon.
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 18, 2:02 PM PST, 7 hours 58 minutes earlier.
Area Forecast Discussion
National Weather Service Pendleton OR
202 PM PST Sat Dec 18 2021
.SHORT TERM...Tonight through Monday...A weather system over
Vancouver Island is moving into southern British Columbia this
afternoon. As it does it will begin pushing a cold front southward
through eastern Washington overnight before stalling along the
Oregon border on Sunday. It will then remain stalled over northern
Oregon and southern Washington through Monday before it begins to
lift northward Monday afternoon. Will see increasing snow into the
Washington Cascades and east slopes overnight as well as the
northern Blue Mountains late tonight and Sunday. Colder air behind
the front will begin to filter into southern Washington and northern
Oregon late Sunday and overnight allowing snow levels to drop to the
lowest elevations of the COlumbia Basin and eastern Columbia River
Gorge. This will change precipitation over to snow allowing for 1 to
4 inches of snow across the lower elevations. To complicate matters
more, a mix of wintry precipitation will also be possible Sunday
night across the lower elevations of northern Oregon. As the cold
front retreats north on Monday some of this wintry mix will shift
into the Washington portion of the Basin. Motorist should be
prepared for winter driving conditions across the Lower Columbia
Basin Sunday night and Monday by allowing extra travel time to reach
your destination. Multiple weather warnings and advisories are in
effect.
.LONG TERM...Monday night through Saturday...Much of the period will
experience a SW flow pattern, making for relatively persistent
precip chances through the week, primarily for the mountains. To
start off the work week, models in good agreement on depicting a cut-
off low centered just off the north Pacific coast, remaining
relatively stagnant through at least the midweek. The precip
forecast will be sensitive to where exactly this system is centered,
but as of now models have most of the flow oriented parallel to the
Oregon coast, so precip chances will be left on the lower end for
the Cascades, mostly dry elsewhere, through at least Wednesday.
Forecast becomes less confident Wednesday onward as ensembles
exhibit large disagreements on how to progress the cutoff low.
Discrepancies seem to stem from the arrival of an upper-level low
digging down from the Gulf of Alaska, which could work to either
absorb the cutoff low to create a much broader system heading
towards the end of the work week, or simply progress through the
forecast area while yet another upper level low works to pick up the
cutoff system and impact the area by around Christmas Day.
Ensembles, however, do seem to agree in depicting a broad system
over the PacNW late in the period, which would make for area-wide
precip chances as well as an encroachment of colder air from the
north. Given the inconsistencies across models during the latter
half of the work week, however, forecast confidence is low, and
would like to see more convergence across model solutions before
headlining any details for the holiday weekend.
The NBM has left persistent PoPs across the forecast period late
Tuesday onward, primarily for our mountain zones. This is most
likely stemming from the synoptic pattern depicting SW flow into our
area most of the week, but overall QPFs look light and not expecting
any real concerns until the latter half of the work week. Snow
levels also look to waver around 1500-2500 ft for much of the
period, closer to 1000 ft around the WA Cascades and eastern
foothills. Will stick with NBM output for now given model
discrepancies, but those planning to travel for the holidays should
keep an eye on the forecast for next weekend. 74
.AVIATION...00z TAFs...VFR conditions expected for the remainder of
the day before a frontal system threatens most sites with precip
later tonight. Breezy south winds, especially for central OR and the
foothills of the Blues, will subside through the night, before a
band of rain showers is expected to settle over most sites beginning
around 04-05z. Precip will start as rain before transitioning
towards snow during the day Sunday, however confidence on the exact
transition time is low. Precip expected to persist much of the day
Sunday, with BDN/RDM not seeing precip mainly until after the
period. Could see MVFR to IFR conditions during the onset of precip,
with IFR and lower conditions more likely during snowfall on Sunday.
74
&&
.PRELIMINARY POINT TEMPS/POPS...
PDT 36 39 29 34 / 90 100 90 80
ALW 38 40 30 35 / 100 100 90 90
PSC 37 41 31 35 / 90 90 80 80
YKM 32 37 28 33 / 30 60 70 90
HRI 36 42 30 35 / 100 90 90 90
ELN 28 35 25 32 / 40 20 40 70
RDM 37 50 33 50 / 20 60 50 20
LGD 33 37 33 40 / 70 90 80 40
GCD 35 44 33 44 / 10 40 40 20
DLS 37 40 32 36 / 90 90 100 90
&&
.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory from 4 AM Sunday to 3 PM PST Monday for
ORZ509.
Winter Weather Advisory from 2 PM Sunday to 3 PM PST Monday for
ORZ041-044-507-508-510.
Winter Storm Warning from 10 PM this evening to 7 PM PST Monday
for ORZ502.
Wind Advisory until 7 AM PST Sunday for ORZ049-507.
WA...Winter Weather Advisory from 2 PM Sunday to 3 PM PST Monday for
WAZ024-027>029.
Winter Storm Warning from 10 PM this evening to 7 PM PST Monday
for WAZ030.
Winter Storm Warning until 7 PM PST Monday for WAZ520.
Winter Storm Warning from 4 AM Sunday to 7 PM PST Monday for
WAZ521.
Wind Advisory until 7 AM PST Sunday for WAZ029.
&&
SHORT TERM...91
LONG TERM....74
AVIATION...74The national radar mosaic for the moment the first event began.
6 heavy snow. Local standard time, as filed.
The Milk Shakes SNOTEL reported 10 inches of new snow during the snow event period. The High Ridge SNOTEL also reported 10 inches of new snow during the snow event period.
An NWS employee 2 miles ENE of Hermiston, OR measured 5 inches of new snow over a 24 hour period. A social media report 4 miles SSW of Hermiston, OR showed that 4 inches of new snow was measured in a 12 hour period.
The cocorahs observer OR-WL-3 1 mile SE of Flora, OR measured 8.5 inches of new snow over a 24 hour period. The cocorahs observer OR-WL-10 2.5 miles SSW of Wallowa, OR measured 6.5 inches of new snow over a 24 hour period.
A social media report from Moro, OR showed 6 inches of new snow was measured over a 24 hour period. A social media report from Dufur estimated that 4.5 inches of new snow had fallen over a 24 hour period.
A trained spotter 5 miles SSW of Chenoweth, OR measured 7.8 inches if new snow in a 24 hour period. A public report from Arlington, OR estimated that 4 inches of new snow had fallen in a 24 hour period ending at 1026 PST on Dec. 20th.
The Clear Lake SNOTEL measured an estimated 9 inches of new snow in a 24 hour period ending at 1100 PST on 12/20.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Oregon in 2021Every state in 2021This day in weather historyWarnings in Oregon, 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: 1004288, 999766, 999764, 999765, 999767, 999768.