A very active storm system in the north Pacific generated large swell directed at the Washington and Oregon coasts that lasted for several days. Additionally the combination of high surf and high astronomical tides contributed to tidal overflow.
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 PQR wrote it up.
A very active storm system in the north Pacific generated large swell directed at the Washington and Oregon coasts that lasted for several days. Additionally the combination of high surf and high astronomical tides contributed to tidal overflow.
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 Portland, OR wrote its last area forecast discussion before the first event at Dec 13, 10:58 AM PST, 32 minutes earlier.
Area Forecast Discussion
National Weather Service Portland OR
1058 AM PST Sun Dec 13 2020
.SYNOPSIS...An active weather will likely continue into next weekend
and bring periods of valley rain and mountain snow every 12-36 hours.
&&
.SHORT TERM...Today through Wednesday...Water vapor satellite imagery
this morning reveals a shortwave trough over the northeast Pacific
and Pacific Northwest. With the main jet support located on the
backside of the upper level trough, the main shortwave trough is
actively digging southeastward into California and the Great Basin.
This left a splitting and weakening front crossing the region
overnight and will leave the best large scale lift going forward to
our south and east. Nonetheless, instability in the post frontal
environment and modest westerly flow of 15-25 kt at 850mb will allow
showers to stream into the region today into tonight. An isolated
thunderstorm or two will be possible along the coast as well with
wind fields marginally supportive of weak rotation.
Snow levels temporarily spiked upward overnight with the front except
near the Gorge, but have since lowered and should hold near 3000 feet
into tonight. The Winter Weather Advisories look on track overall
with at least another 4-10" of snow likely to fall across most of
the Cascades above 3000 feet through tonight.
Within the central Columbia River Gorge, temperatures did lower to
right around 32F, but precipitation intensity and road temperatures
have largely kept snow from sticking to roads and kept accumulations
light and short lived between Cascade Locks and Hood River. However,
the story is different just a bit higher in elevation with several
reports of 1-3" of snow falling overnight into this morning closer
to 1000-1500 feet in the upper Hood River Valley and along the WA
side of the Gorge. As easterly pressure gradients begin to relax
today, expect temperatures to moderate, which will allow some
thawing below 1000 feet. However, am a bit worried that the upper
Hood River Valley may remain close enough to freezing that a more
sustained thaw will not occur until Monday given pressure gradients
do not open more solidly until late tonight into Monday morning.
Models remain in good agreement shortwave ridging will push into the
Pacific Northwest beginning late tonight and Monday. This will result
in shower intensity and coverage gradually decreasing late tonight
through Monday. Have kept PoPs considerably higher than the NBM 6
hour PoP chances through Monday afternoon given model soundings
suggest plenty of instability, moisture and onshore flow will
maintain at least showers across the area, particularly across the
higher terrain and our more northern zones. HREF guidance supports
this idea as well.
As the atmosphere further stabilizes late Monday, expect the threat
of showers to decrease to near zero Monday evening before the next
storm system impacts northwest Oregon and southwest Washington late
Monday night into Tuesday. Given the main upper level support for
this front will remain across southern British Columbia, expect this
front to be weakening as it moves into the region. Nonetheless, it
will bring another round of valley rain and mountain snow with
precipitations amounts remaining rather light.
A shortwave ridge should then race across the Pacific Northwest
Tuesday night and result in rain chances temporarily decreasing
before the next storm system arrives Wednesday. Models and their
ensembles continue to vary on the strength and track of a low
pressure offshore, but there are certainly some scenarios that would
bring quite a bit of wind to at least our coast and a significant
shot of rain and high snow levels on Wednesday. Will dig deeper with
the afternoon forecast package.
Also, it should be noted that we will be entering a period of king
tides today through Tuesday so there will likely be some minor tidal
overflow flooding in the usual spots near Raymond and outside of
Tillamook during the high tide around midday. In addition, a
powerful westerly swell will create marginal high surf conditions
along our coastline today and possibly again Tuesday. Minor beach
erosion will be possible with each event, but the biggest story with
this will likely be the renewed threat of sneaker waves along our
coastline both days. /Neuman
.LONG TERM...Wednesday night through Saturday...No Changes...Previous
discussion from 300 AM Sunday follows...A brief break Wednesday night
as weak high pressure developing on the leading edge of a deepening
low pressure system. This low pressure system is showing a sea level
pressure around 990 mb but it has very little upper level support
from the jet stream which may cause it to weaken through time. Even
with the lack of synoptic support, models are showing quite a lot of
precipitation and gusty winds associated with this event. The low
looks to float around in the eastern Pacific
where it spins through the day on Wednesday. This would mean that
precipitation would likely remain pretty constant through the day
which will bring larger snowfall accumulations than what is expected
with the Tuesday system. This low will follow a similar trend to the
front on Tuesday with an influx of warmer air at the surface. Because
of this, snow levels will rise back from 2000 feet to around 5000
feet through the day. Thus, most snow will likely be at higher
elevations during the peak precipitation. The low will weaken and
dissipate as it moves inland on Thursday. This pattern looks very
similar in strength to the early depictions of the system that will
be making landfall on Tuesday. Thus, there is a lack of confidence
with the overall outcome. There will likely be several iterations
with the forecast as numerical models hone in on both the strength
and track of this storm. Friday and through the weekend, some models
are suggesting the potential of a weak atmospheric river with an the
probability of IVT greater than 250 kg/(ms). While others are
showing a rather robust low moving into the area. Given the
uncertainty have chosen to go with the NBM and continue to watch as
these systems develop. -Muessle/42
&&
.AVIATION...Region remains in a moist and unstable onshore flow
today and tonight. Predominantly MVFR flight conditions can be
expected over the next 24 hours, with a chance for IFR conditions
throughout that period, mainly in the interior valleys. The
central Oregon coast looks like the best chance for seeing
conditions improving to VFR later today, after about 21Z.
Showers can be expected to continue off and on throughout the
region, with a slight chance for thunderstorms through this
evening near the coast.
For detailed regional Pac NW weather information, go online to:
http://weather.gov/zse
KPDX AND APPROACHES...Mainly MVFR conditions expected over the next
24 hours in a showery air mass. There is a chance for seeing IFR
conditions at times both today and tonight.
&&
.MARINE...A cold front moving across the waters overnight will move
inland early this morning. Winds, gusting to 30 to 35 kt along and
just ahead of the front, will drop to 20 kt or less behind the front
today as the wind direction veers to the southwest. The next system
of interest is a frontal system reaching the coastal waters Monday
night, and moving east through the waters by Tuesday morning. Not
unlike the current front moving through, this system appears likely
to bring gale force wind gusts, mainly to the outer waters as it
moves through.
Seas are expected to build this morning, initially dominated by
steep wind waves and fresh swell generated by the local winds. A
long period swell is expected to arrive late in the morning, and
continuing to build through the afternoon. Current expectations are
for seas to peak in the range of 17 to 20 ft late this afternoon
through about midnight tonight, before subsiding Monday and Monday
night. A high surf advisory will be in effect for the coast from
noon Sunday through Sunday night. Another large long period swell
will be possible following the next front late Tuesday into
Wednesday.
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...High Surf Advisory until 6 AM PST Monday for Central Oregon
Coast-North Oregon Coast.
Coastal Flood Advisory until 1 PM PST this afternoon for North
Oregon Coast.
Winter Weather Advisory until 4 PM PST this afternoon for Upper
Hood River Valley.
Winter Weather Advisory until 4 AM PST Monday for Cascades in
Lane County-Northern Oregon Cascades.
WA...High Surf Advisory until 6 AM PST Monday for South Washington
Coast.
Coastal Flood Advisory until 1 PM PST this afternoon for South
Washington Coast.
Winter Weather Advisory until 4 AM PST Monday for South
Washington Cascades.
PZ...Small Craft Advisory until 6 PM PST Monday for coastal waters
from Cape Shoalwater WA to Florence OR out 60 NM.
Small Craft Advisory until 6 AM PST Monday for Columbia River
Bar.
&&
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www.twitter.com/NWSPortland2 high surf, 1 coastal flood. Local standard time, as filed.
The tide gage at Astoria, OR reported water levels exceeding 10.5 feet during the higher high tides from the 13th to the 16th. The water levels during higher high tides were 10.5 feet at 1130PST on the 13th, 10.5 feet at 1212PST on the 14th, 10.8 feet at 1306PST on the 15th, and 10.8 feet at 1354PST on the 16th.
Buoy 46050, Stonewall Bank, off the central Oregon coast reported wave heights exceeding 20 feet at 15 seconds at 1640PST on the 13th, peaking at 23 feet at 15 seconds at 2240PST on the 15th. Waves subsided below high surf criteria on the afternoon of the 16th.
Buoy 46041, Cape Elizabeth, off the Washington coast reported wave heights exceeding 20 feet at 17 seconds at 2040PST on the 13th. Wave heights dropped some on the 14th and 15th. Waves then picked up again on the 16th, this time peaking at 25 feet at 17 seconds at 2240PST on the 16th. Waves subsided below high surf criteria on the morning of the 16th.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Oregon in 2020Every state in 2020This day in weather historyWarnings in Oregon, December 2020
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: 934944, 934926, 934931.