A strong atmospheric river brought heavy rains on December 5th which led to minor river and urban flooding across portions of southwest Washington. Clark County and Cowlitz County saw landslides, along with minor river flooding, including the Cowlitz River at Kelso and the Grays River near Rosburg.
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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 strong atmospheric river brought heavy rains on December 5th which led to minor river and urban flooding across portions of southwest Washington. Clark County and Cowlitz County saw landslides, along with minor river flooding, including the Cowlitz River at Kelso and the Grays River near Rosburg. Portions of the Willapa Hills and south Washington Cascades received 12 to 16 inches of rain over a 5 day period beginning December 1st.
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 4, 10:14 AM PST, 16 minutes earlier.
Area Forecast Discussion...UPDATED
National Weather Service Portland OR
1014 AM PST Mon Dec 4 2023
Updated public and aviation discussion...
.SYNOPSIS...Rain showers continue today before yet another
atmospheric river will bring periods of moderate to heavy rain
to the area tonight through at least Tuesday night with showers
and thunderstorm chances Wednesday. As such, river flooding and
urban flooding will remain a concern through at least Wednesday
afternoon. A colder frontal system immediately behind the
atmospheric river will bring more rain Thursday, albeit
relatively lighter, as well as Cascade snow. Signals indicate
the potential for another weaker atmospheric river Friday into
the weekend.
&&
.SHORT TERM...Today (Monday) through Wednesday...UPDATE: Current
radar imagery and observations as of 10am PST show rain showers
continuing over southwest WA, the Cascades, the Coast Range as a warm
front lifts over southwest WA. Since 7am PST, most locations in the
Willamette Valley have received less than two to three hundredths of
an inch. Meanwhile, a few RAWS stations in the north Oregon Coast
Range, Willapa Hills, south WA Cascades, and north OR Cascades near
Mt. Hood (all above 2500-3000 ft) have received around 0.40-0.60 in
of precipitation. Expect mostly light showers to continue today
before the next atmospheric river arrives this evening.
Most of the rivers that rose rapidly yesterday along with smaller
creeks and streams have peaked or are near their peaks and will be
lowering through today. Urban flooding concerns have also decreased
as widespread rain diminished, though roads will likely remain wet
and slippery. This period of limited to no rainfall will be short
lived as the next weather system approaches the region. A stationary
front currently stalled along the OR/WA border will transition into a
warm front later this morning. Showers will increase spatially
near and long this boundary this morning as well as over the
terrain due to orographics as a cold front approaches, though
rain rates will remain fairly limited through this afternoon.
Urban flooding and river flooding concerns will increase again
tonight through Tuesday night as yet another atmospheric river
(AR) takes aim at southwest WA and northwest OR and brings more
moderate to heavy rain to the area. A Flood Watch remains in
effect for locations west of the Cascades through Wednesday
afternoon to cover this threat. The GEFS/EPS continue to suggest
this will be a strong atmospheric river with IVT values peaking
around 850-900 kg/ms. That being said, the GFS/EURO continue to
show very weak synoptic scale and mesoscale forcing. This means
rain rates may not get as high as the strength of the AR would
suggest, which could result in total rain amounts that are less
than expected. Latest forecast has slightly lowered total rain
accumulations, though not enough to limit flooding concerns. In
addition, confidence is moderate regarding the exact duration of
the heaviest rainfall with this system. Right now, most model
guidance suggests a prolonged period of moderate to heavy rain
for 36-48 hours from around late tonight through Tuesday night
as the cold front slowly pushes inland and is slated to very
slowly move through the region. There remains uncertainty in how
long it will take the cold front to move through, with most
guidance showing it stalling throughout Tuesday before pushing
east of the area sometime on Tuesday night or Wednesday
morning.
Post frontal showers will persist through the day Wednesday as
the remnants of the AR continue to shift eastward. Will mainly
be showery, but will still see additional accumulations. Overall
the flow is fairly messy and unorganized, though some bands of
increased vorticity advection paired with the region having
upper air support from the jet stream indicates thunderstorm
potential in the late afternoon and evening, especially along
the coast.
Despite the ongoing uncertainty in specifics of the next three
days, river levels will already be elevated going into this next
AR event. This means river flooding will remain a concern
through Wednesday, even if observed rain amounts wind up a bit
less than the current forecast. Forecast rain amounts and
expected impacts for the system are discussed below in the
hydrology discussion. -HEC/TK/Muessle
.LONG TERM...Thursday through Sunday...Thursday a weaker cold
front will move in bringing yet another round of showers. This
system is not an AR, but rather a true airmass shift. A cold air
wrapped low aloft will move over Vancouver Island through the
day. This cold front will also bring cooler temperatures in
comparison to what we will experience early this week. 850 mb
temperatures will be around -3 deg C which will drop daytime
temperatures into the 40s for the lowlands and 30s for the
mountains. WPC 500 mb cluster analysis indicates uncertainty in
the exact track of the low, which will impact the area of
heaviest precipitation along the West Coast. Either way, snow
levels will be dropping due to colder temperatures, so snow at
the passes is likely, though uncertainty remains in exactly how
much snow will fall. Latest forecast indicates 6-14 inches of
snow above 3000-3500 feet, which is much higher than the
previous forecast. NBM v4.1 indicates 50-90% probability of 4+
inches of snow for all of the Cascades from central OR to
southern WA. Additionally, it indicates 50-80% probability of 8+
inches of snow and 12+ inches of snow for the Cascades south of
Clackamas County and northeastern Skamania County.
On Friday through Saturday, there is a 50-70% probability
for another weak to moderate AR based on GEFS/EPS guidance.
However, the pattern is not necessarily "text book" as in that
guidance shows a warm airmass converging with a much cooler
airmass from the north. Expect precipitation to continue Friday
through the weekend, but at this point, confidence is low in
specific amounts. -Muessle/HEC
&&
.HYDROLOGY...Periods of moderate to heavy rain will continue
through Wednesday, with the heaviest tonight through Tuesday
night as a strong atmospheric river aims at southwest Washington
and northwest Oregon. This is also when flooding concerns are
highest. Additional rain amounts expected between 4am PST Monday
and 4am PST Wednesday (48 hour rain totals): 3 to 5 inches
along the south Washington coast, north Oregon coast, and
central Oregon coast, 3 to 5 inches with localized amounts up to
7.5 inches over the Coast Range and Willapa Hills (highest
amounts in higher terrain), 1.25 to 2.5 inches across the
interior lowlands of southwest Washington and northwest Oregon
(highest from Salem northward), 1 to 7 inches across the south
Washington and north Oregon Cascades, 0.25 to 1.5 inches for
the Lane County Cascades, 2 to 4 inches for the Columbia River
Gorge, and 1 to 2 inches for the Upper Hood River Valley.
River levels following the heavy rain yesterday morning have
peaked and are lowering. Given the forecast rainfall amounts
expected through the middle of the week, river levels will rise
again late tonight through Wednesday. Forecasts for most rivers
indicate a higher peak than the previous peak Tuesday afternoon
into Wednesday morning since river levels will remain elevated.
Most coastal rivers show a 15-40% chance of reaching minor
flood stage at some point within the next 10 days. This includes
the Naselle River near Naselle, the Nehalem River near Foss,
the Nestucca River near Beaver, the Grays River near Rosburg,
and the Siletz River at Siletz. The Wilson River near Tillamook
has the best chance of reaching minor flood stage as the
probability has increased to 65%. Probabilities for major
flooding along coastal rivers are around 15% or less.
Additionally, many other rivers across northwest OR and
southwest WA are showing anywhere from a 5-35% chance of
reaching at least minor flood stage in the next 10 days, except
for the mainstem Columbia and Willamette Rivers where the chance
of reaching minor flood stage remains lower at 5% or less. While
these probabilities have decreased from previous forecasts,
there is the potential for probabilities to increase again if
QPF amounts increase with future model runs. To view current and
forecast river stages for any river gage location across
southwest WA and northwest OR, visit
https://water.weather.gov/ahps2/index.php?wfo=pqr
Lastly, urban flooding is possible Monday night through Wednesday,
especially in low-lying areas with poor drainage. Significant
ponding of water and localized roadway flooding is expected on
roads. Any motorists with travel plans should also allow extra
time for their commute as hydroplaning will be a risk. Never
drive through flooded roads. -TK/HEC
&&
.AVIATION...18Z TAFs: Radar imagery shows post frontal showers
continuing on the leading edge of yet another atmospheric river
(AR) which will move over the area after 00Z Tuesday. The AR will
shift from north to south with the southern portions of Washington
experiencing the wind and rain first, then it will weaken as it
moves southward. This AR will bring gusty winds, and heavy rain
which will impact visibility and LLWS. CIGs are less of a concern
about drastic drops to IFR levels. Rain rates will be high enough
to potentially cause some pooling water on area runways or lower
lying areas around terminals. Winds will be southerly, and will
amplify after 05Z Tuesday. Gusts as high as 40 kt along coastal
terminals due to the strong southerly flow. Will note that at
about 1000 ft, winds could be as high as 50 kt along coastal
terminals and at around 1000 ft. Inland sites will see less wind,
though airports are not out of the woods. In the Willamette
Valley, those southerly winds will be amplified due to the
terrain. LLWS is likely over inland sites. At 1000-2000 ft, winds
are around 45 kt, and at 3000-4000 kt closer to 55 kt.
KPDX AND APPROACHES...A mix of MVFR and VFR conditions through the
day. The atmospheric river will bring increased winds and rain.
E-W aligned runways will experience higher rates of wind shear,
especially when the system passes between 09-15Z Tuesday. This
will be the period of heaviest rain and strongest winds. Below
1000 ft, gusts are around 35-40 kt. Not necessarily expecting
surface winds to gust to 40 kt, but will still be quite windy.
Pooling water is possible during the periods of heaviest rain.
-Muessle
&&
.MARINE...Gales have redeveloped overnight into Monday morning
across the waters. Gales may be prolonged as the tight pressure
gradient remains over the waters into Monday night before the
front move ashore Tuesday morning. May even see a brief period of
storm force winds Monday evening but latest models have backed off
slightly on that idea. These storm force winds are not wide spread
enough to issue a storm warning at this point.
Seas approaching 20 ft on Monday. GWES probabilistic guidance
shows about a 50% chance for seas exceeding 20 ft Tuesday morning.
There is another batch of swell arriving Tuesday afternoon. GWES
probabilistic shows about 90% seas exceed 20 ft, but less than 10%
for exceeding 25 ft.
Also with the elevated seas continuing through mid-week, will
maintain the threat of sneaker waves along our coast. -JH
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Flood Watch through Wednesday afternoon for Cascade Foothills
in Lane County-Central Coast Range of Western Oregon-Central
Oregon Coast-Central Willamette Valley-Coast Range of
Northwest Oregon-Greater Portland Metro Area-Lower Columbia-
North Oregon Coast-Northern Oregon Cascade Foothills-South
Willamette Valley.
WA...Flood Watch through Wednesday afternoon for Greater Vancouver
Area-I-5 Corridor in Cowlitz County-South Washington
Cascade Foothills-South Washington Coast-Willapa Hills.
PZ...Flood Watch through Wednesday afternoon for Coastal waters from
Cape Shoalwater WA to Cape Falcon OR out 10 NM.
Gale Warning until 10 AM PST Tuesday for Coastal waters from
Cape Shoalwater WA to Florence OR out 60 NM.
Hazardous Seas Warning from 10 AM to 4 PM PST Tuesday for
Coastal waters from Cape Shoalwater WA to Florence OR out
60 NM.
Gale Warning until 8 AM PST Tuesday for Columbia River Bar.
Small Craft Advisory from 8 AM to 4 PM PST Tuesday for Columbia
River Bar.
&&
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www.twitter.com/NWSPortlandThe national radar mosaic for the moment the first event began.
3 flood, 1 heavy rain. Local standard time, as filed.
The Grays River rose above flood stage on December 4th, cresting at 16.24 feet on December 5th at 9 am, and fell below flood stage on December 6th. Flood stage is 12.0 feet.
The AMTRAK rail experienced a small landslide on their track between mile marker 129 and 130.5 near Felida and canceled the train between Seattle and Portland through December 7th. No impacts other than their internal transportation delays occurred.
The Willapa River at Willapa rose reached minor flood stage during a period of 1 and half hours, cresting at 21.03 feet at 315 pm on December 5th.
Heavy rain produced minor flooding along the Cowlitz River at Kelso. The river crested at 22.10 feet at 12 pm on December 6th. Flood stage is 21.5 feet.
A landslide also occurred on the 503 Spur Road which cut off the community of Cougar in Cowlitz County.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Washington in 2023Every state in 2023This day in weather historyWarnings in Washington, December 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: 1160580, 1160548, 1160583, 1160546.