Warm air aloft and cold pooling in valley areas combined with an upper trough influencing the regions weather resulted in freezing rain developing across portions of the east slopes of the Washington Cascades and portions of southeastern and south central Washington over Dec. 26th and 27th.
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The episode as NWS PDT wrote it up.
Warm air aloft and cold pooling in valley areas combined with an upper trough influencing the regions weather resulted in freezing rain developing across portions of the east slopes of the Washington Cascades and portions of southeastern and south central Washington over Dec. 26th and 27th.
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 26, 3:50 AM PST, 10 minutes earlier.
Area Forecast Discussion
National Weather Service Pendleton OR
350 AM PST Mon Dec 26 2022
Updated Aviation Discussion
.SHORT TERM...
Today through Wednesday...Two weather systems will bring impacts
across the region over the next couple of days.
The first system, will be moving onshore in western Oregon and
Washington later this morning. For the most part, most of the
impacts will be confined to the Cascades and west early, with low
pops elsewhere and increasing through the day. The biggest issue
with this first system remains the cold temperatures and the
potential for at least some freezing rain for the Yakima Valley,
Kittitas Valley, Gorge and Columbia Basin. Temperatures are
forecast to be slowly rising through the day and be above freezing
this by this evening, but the thermometer has yet to respond and
cold air often shows its stubbornness in leaving after it has
been around for awhile.
Confidence is lower today on the areal extent and amount of
freezing rain. The 26/00Z guidance has lower QPF and overall with
this first batch and most if not all of it is much less bullish on
freezing rain potential. Not to say it won't happen, but just not
as confident as would otherwise be. For every moment that the
precipitation remains west of the area, that gives temperatures
time to hopefully warm up before precip moves in. For right now,
will leave the winter weather headlines in effect unchanged.
Then, later this evening into Tuesday, a second and stronger
storm will move across the area. This well advertised system will
bring rain for the most part and warmer temperatures everywhere.
Strong low pressure will move into British Columbia Tuesday
morning. In advance of the low, a warm front will bring rain and
cause rising snow levels. There could still be some mixed
precipitation over the mountains at the onset, but then all rain
is undissipated, and it could be heavy at times over the mountain
areas as an atmospheric river event sets up. As is often the
case, pops and QPF will be least in the Basin, most in the
mountains and in between elsewhere. Precipitation begins to taper
off Wednesday as the low moves away from the region.
From a rainfall and hydrology perspective, it still looks like
upwards of 2 to 3 inches in the Cascades and 1 to 2 inches in the
Blue Mountains (with locally higher amounts). These amounts of
rainfall coupled with warmer temperatures...30s and 40s in the
mountains and 40s and 50s elsewhere will lead to snowmelt and
runoff. At this point, it appears that while there will be many
in-banks rises and some streams and rivers will reach caution
stage, no flooding is anticipated. Between 0.25 to 0.50 inches is
expected most elsewhere. The EFI keys in on 0.8 to 0.9 for
portions of eastern Washington including the Blue mountains an
Blue Mountain foothills.
The other significant impact with this system is due to the
strength of the low, there is a very tight pressure gradient.
There is very high confidence in strong winds (90%) beginning
tonight and continuing into Wednesday morning, with the peak
Tuesday afternoon. The strongest winds look to be over central
Oregon and portions of the Basin and Gorge. Wind advisory level
gust look likely, and high wind warnings can not be ruled out for
at least a portion of the area. A wind advisory will be issued
with the morning forecast. Virtually every piece of guidance has
been sending a strong signal for winds during this period and it
is corroborated by the ECMWF EFI which has a 0.8 to 0.9 for most
of Oregon and 0.9 to 0.95 of a portion of the Basin and central
Oregon. Also 0.8 to 0.9 for wind gust for most of the state.
Additionally, winds win the Grand Ronde Valley are gusty morning
and a wind advisory remains in place there until later this
morning.
High temperatures today will be in the 30s in most area, to near
50 in central Oregon. However, highs could actually come later
today or this evening as temperatures continue to rise especially
across the Basin. Tuesday will be the warmest day of the week, and
in many parts of the region, in quite some time. Everyone will be
above freezing with highs in the 40s and 50s. Wednesday will be a
bit cooler with highs mainly in the low to mid 40s. Overnight lows
Tuesday morning will be in the 30s and in the 30s and 30s
Wednesday morning.
.LONG TERM...
Wednesday night through Monday...Model guidance in great
agreement that an active period of weather will continue through
the latter half of the work week, with a reprieve from
precipitation possible over the weekend.
Overnight Wednesday, winds are expected to continue to weaken and
precipitation chances retreat to mountain zones as a potent
surface low and upper trough exit the region. By early Thursday, a
weakening frontal system and shortwave will quickly move across
the PacNW with light snow in the mountains, a wintry mix in the
Yakima and Kittitas valleys, and light rain in the lower
elevations. This system will quickly be followed up Thursday night
through Friday with a slightly stronger and wetter frontal system
coupled with an upper shortwave trough. This will provide at
times more moderate snow accumulations in the mountains while the
lower elevations continue to see light rain. Meanwhile, the Yakima
valley will see the wintry mix transition over to rain through
Friday, while the Kittitas valley may still see a light wintry
mix through the same period. By Saturday, very light precipitation
will continue across mountain zones as an impulse in northwest
flow aloft passes over the forecast area, then drying out Sunday
as a transient upper ridge moves over the region. Starting
Thursday, a gradual cooling trend is expected as each shortwave
and frontal system pushes cooler air into the region, with
temperatures moderating by the first of next week.
Overall, ensemble and deterministic model guidance is in good
agreement with the evolution of the synoptic pattern Wednesday
night through the weekend. However, there are slight timing
differences apparent between the GFS and ECMWF guidance, with the
ECMWF generally 3 to 6 hours earlier than the GFS with each
system through the late Friday. Investigating the 500mb clusters
also indicates that the leading 500mb EOF variance is centered
around differences in the strength of each shortwave system.
Though these strength differences have minimal changes on the
precipitation impacts, the impacts would be seen in the
temperatures, where cluster solutions dominated by the ECMWF
through Saturday would result in slightly warmer afternoon
temperatures as compared to those solutions dominated by the GFS.
As for precipitation, atmospheric river (AR) probabilistic tools
indicate very low chances (5-15%) of even a minor AR developing
through the latter half of the week, resulting in moderate
confidence of light to locally moderate precipitation
accumulations. Lawhorn/82
.AVIATION...12Z TAFs...Mostly VFR to MVFR conditions will prevail
through the period, however IFR to LIFR conditions will continue
at sites DLS/YKM. Low CIGS at sites DLS/YKM will persist through
the period, though periodic lifting to MVFR may be possible as
incoming system moves through the area. LIFR vsby will also
continue at site YKM over the next couple hours, becoming IFR to
MVFR as weather system moves through the area. This morning, band
of precip consisting of light freezing rain will impact sites
DLS/PDT/YKM/ALW/PSC through 18Z-20Z. Light freezing rain will
transition to light rain at site DLS by 20Z and persist through
the period. Persistent light rain at sites RDM/BDN will begin at
after 20Z, while all other sites will see prevailing light rain
begin after 00Z. Expect deterioration of CIGS and vsby to MVFR
with prevailing light rain this afternoon and evening. Winds
mainly be light through the period, except at sites RDM/BDN where
winds will increase to 15-20kts with gusts up to 30kts possible
after 04Z. Lawhorn/82
&&
.PRELIMINARY POINT TEMPS/POPS...
PDT 45 39 51 36 / 40 80 30 30
ALW 45 40 51 39 / 60 100 40 40
PSC 37 33 48 39 / 40 90 30 20
YKM 37 31 43 30 / 60 90 60 50
HRI 40 35 51 39 / 40 90 20 20
ELN 37 31 40 29 / 50 90 60 50
RDM 50 41 49 31 / 70 90 70 50
LGD 41 38 45 34 / 60 100 50 50
GCD 46 40 47 32 / 40 100 40 20
DLS 43 39 50 40 / 80 100 90 80
&&
.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Ice Storm Warning until 10 PM PST this evening for ORZ041.
Wind Advisory from 10 PM this evening to 10 AM PST Wednesday for
ORZ041-044-507-508-510-511.
Wind Advisory until 10 AM PST this morning for ORZ049.
Wind Advisory from 4 AM Tuesday to 10 AM PST Wednesday for
ORZ050.
WA...Ice Storm Warning until 10 PM PST this evening for WAZ024.
Wind Advisory from 10 PM this evening to 10 AM PST Wednesday for
WAZ024-521.
Wind Advisory from 4 AM Tuesday to 10 AM PST Wednesday for
WAZ028-029.
Ice Storm Warning until 4 AM PST Tuesday for WAZ026-027.
Winter Weather Advisory until 4 AM PST Tuesday for WAZ028.
&&
SHORT TERM...77
LONG TERM....82
AVIATION...82The national radar mosaic for the moment the first event began.
1 ice storm. Local standard time, as filed.
A Co-Op observer in Sunnyside, WA measured 0.25 inches of ice accumulation from freezing rain from the previous evening at 0200 PST on Dec. 27th. Via a public report from Granger, WA, 0.25 inches of ice accumulation from freezing rain was reported at 0200 PST on Dec. 27th.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Washington in 2022Every state in 2022This day in weather historyWarnings in Washington, December 2022
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: 1073311.