An atmospheric river brought mild temperatures and heavy rain to Northeast Washington. The mild temperatures caused snowmelt in the low to mid elevations.
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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 OTX wrote it up.
An atmospheric river brought mild temperatures and heavy rain to Northeast Washington. The mild temperatures caused snowmelt in the low to mid elevations. The rapid melt and rain amounts of an 1.0-1.5 caused flooding issues.
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 Spokane, WA wrote its last area forecast discussion before the first event at Apr 10, 2:16 AM PST, 44 minutes earlier.
Area Forecast Discussion
National Weather Service Spokane WA
316 AM PDT Mon Apr 10 2023
.SYNOPSIS...
A wet and mild storm system through Tuesday will deliver copious
amounts of rainfall and snow melt leading to increased flows
within the rivers, streams, and creeks of eastern Washington and
the northern Idaho Panhandle. Temperatures will be mild with highs
ranging from the lower 60s to upper 70s degrees, particularly over
the southeast portion of the forecast area. Cooler temperatures
return by Tuesday with showery precipitation through the middle
part of next week. Next weekend looks dry with temperatures
warming above normal.
&&
.DISCUSSION...
...MILD TEMPERATURES WITH LOW TO MID ELEVATION SNOW MELT AND
MODERATE TO HEAVY RAIN WILL RAISE CONCERNS FOR MINOR FLOODING
IMPACTS EARLY THIS WEEK...
Today through Monday night: A weak to moderate Atmospheric River
(AR1 to AR2) event is underway over the Inland Northwest. This has
been a well advertised AR event over the last few days and
current observations reflect what the model ensemble means have
been indicating. This event is just getting started and it's both
the magnitude of the sub-tropical moisture plume (3-4 standard
deviations) and length of time that categorizes this event as
borderline weak to moderate. The latest model guidance is showing
more of a weak AR event than a moderate one, so I'm confident that
impacts will likely be minor but still a number of potential
issues to monitor. Little changes were made to the forecast. The
firehose of moisture will pivot westward a bit through the morning
and afternoon hours today. This will result in a reprieve of
rainfall over the southeast portion of the forecast area with the
leading edge of the stratiform band retrograding to along a line
of around Lind/Ritzville to Spokane/Deer Park to Sandpoint/Bonners
Ferry by this afternoon. Moderate to locally heavy rain will
primarily be focused right along the Cascade crest and and across
north-central Washington, and in particular across the Okanogan
Highlands to the Northeast Mountains for this afternoon. The
reason for this pivot westward will be due to the upper level
trough offshore that will undergo further digging as a shortwave
disturbance rounds the base of the trough and orients the upper
level jet more meridional. The upper level trough then will eject
across the region Monday night swing through a dynamic cold front
when the heaviest precipitation is expected to occur along the
front. Temperatures are also quite mild with the AR resulting in
low to mid elevation snow melt to go along the rainfall depending
on your location. The next 36 hours will primarily be a heavy
rain, snow melt, and potential for flooding concerns with other
associated impacts:
* Additional rainfall amounts: Over the next 24 to 36 hours, the
focus for heaviest rainfall will be over Okanogan Highlands to the
Northern Panhandle where widespread 1+ inches is expected. Up to
1.5 inches will be possible for most valleys with 2-2.5 inches
possible in Selkirks where the heaviest rainfall totals are
expected. This will be in addition to the 0.10 to 0.25 inches that
will have fallen through the early morning today. These valley
locations including Colville, Chewelah, Northport, Newport,
Sandpoint, and around Priest lake will see a 40-70% chance of over
an inch of additional rainfall through Tuesday morning; there's
less than a 5% chance that these areas will see up to 2 inches of
additional rainfall. Much of the rest of the region will also be
wet. The basin over the central Idaho Panhandle will see 0.50 to
1.00 inches over this same period.
* Impacts: There is a minor risk to flooding impacts where the
heaviest rainfall is expected over northeast Washington into the
Northern Panhandle region. The concern is mainly due to the
influence of snow melt. Some valley locations such as around
Priest Lake still have snow on the ground. Any homes that have
snow around them, could see the potential for water seepage into
basements. Low lying areas are likely to see minor flooding as
soils become saturated. Small streams and creeks will see
significant rises and will need monitoring. Good news is that
mainstem rivers are starting out with base flows that are low, and
this event doesn't appear to be significant enough to raise
concerns for flooding on rivers. The Little Spokane River is in
that sweet spot where it will receive significant rainfall with a
small contribution of snow melt that it will see a significant
rise and is anticipated to crest right near bankfull come Tuesday
afternoon/evening. The rest of the region will mostly receive
welcoming rains, especially in the basin and north-central
Washington where it is needed. Flashy creeks in the southern to
central Idaho Panhandle (e.g. Paradise Creek) will see a sharp
rise, but the heavy rain with the front looks to pass through fast
enough that I think these creeks will behave. This is also a good
pattern for rock slides and another impact to keep in mind,
especially in steep terrain.
We will monitor the hydrology situation as the AR pushes through.
The Flood Watch looks good. I anticipate that any impacts that occur
will be of more of a nuisance than anything that may warrant a flood
advisory at some point. I would be surprised if impacts reach the
level of needing a flood warning. Impacts outside of the flood watch
areas will mainly be for ponding of water in low lying areas as the
cold front sweeps through Monday night into Tuesday morning. May
also see the potential for rock slides in steep terrain,
particularly in the Idaho Panhandle.
A secondary impact will be for developing convection over southeast
Washington into the central Idaho Panhandle ahead of the stratiform
rain Monday evening. There is enough instability at low to levels to
warrant a slight chance for thunderstorms where infrequent cloud to
ground lightning, pea sized hail, and heavy downpours will be
possible -- essentially from around Pomeroy to Pullman/Moscow to
Couer d'Alene/Pinehurst/St. Maries.
Decreasing precipitation across the southeast portion of the
forecast area will allow for another warm and muggy afternoon. Highs
in the upper 70s is expected for the Lewiston-Clarkston Valley. A
high of 80 looks less likely with recent model trends, but not out
of the question. This is in stark contrast to where the rain will be
focused this afternoon with highs generally in the low to mid 50s
for Wenatchee, Moses Lake, Methow Valley, and Okanogan Valley.
Tuesday through Wednesday: The upper level trough of lower pressure
will swing over the region on Tuesday. Temperatures and snow levels
will plummet once again. High temperatures on Tuesday will be in the
upper 40s to low 50s for most valleys -- a 20-25 degree temperature
swing in the Lewiston-Clarkston Valley. The Polar Jet Stream will
sag south of the region with colder temperatures aloft and placing
the Inland Northwest in a conditionally unstable environment.
Scattered showers will develop. Dew point temperatures will crash
hard behind the front though in the lee of the Cascades. All this
dry air will limit shower development over the Columbia Basin.
Better chances for showers will be over the northern mountains and
in the Idaho Panhandle. Thermal profiles will cool to the point that
precipitation type is expected to be as convective snow showers,
snow pellets, and/or graupel showers. A stray lightning strike
cannot be ruled out with this convection, but lifted condensation
levels (LCLs) will be on the cold side and may difficult to achieve
enough charge separation for thunderstorms. Wednesday will be
similar with diurnally driven convective showers. Snow melt will
effectively cease at mid and upper elevations, which will help to
allow creeks, streams, and rivers to recede. /SVH
Wednesday night through Sunday: Ensembles suggest the trof overhead
containing a cold conditionally unstable airmass will show some
slight moderation as the trof axis move slowly east which allow
Eastern Washington and North Idaho to be influenced more by the
northwest flow on the far west side of the trof Friday morning and
not so much by any small scale features nested in the trof. With
this scenario in mind any lingering pops are primarily positioned
within vicinity of the Cascade Crest and over portions of North
Idaho with the low wet bulb zero heights provided by the cold trof
keeping snow levels fairly low so mostly snow is mentioned. Upper
level ridging moves in Friday night allowing for drying (and
warming) over the weekend, however by Sunday the upper level ridge
axis is pushed into Montana and a plume of moisture running up
southwest to northeast along the west edge of of it streams into
Eastern Washington and North Idaho. This will allow the warming
trend to continue but coupled with considerable cloud cover along
with the potential for some light rain with snow levels mostly above
6000 feet MSL Sunday. /Pelatti
&&
.AVIATION...
06Z TAFS: The transition from VFR to MVFR has begun with the
incoming rain. By 09-12Z Latest HREF guidances still showing some
increased probabilities around 30-40% of local IFR conditions
developing around Wilbur, Moses Lake, and Ephrata between 07-15Z.
Rain will taper off across southeastern WA and lower Idaho
Panhandle Monday morning retreating back into Central and Northern
WA for a few hours. Moderate to heavy rain intensities expected
to develop Monday evening around 04-06Z. Lightning strikes will
be possible (10-20% chance) ahead of the front along the ID/WA
border but the more widespread aviation impact will be local IFR
under these heavier rain bands. /db
&&
.PRELIMINARY POINT TEMPS/POPS...
Spokane 62 41 50 29 48 29 / 80 100 60 20 30 0
Coeur d'Alene 62 41 49 30 47 29 / 80 100 90 30 40 10
Pullman 69 39 47 29 45 28 / 30 100 90 20 50 10
Lewiston 78 47 56 35 51 34 / 20 90 90 10 40 10
Colville 53 39 52 26 51 26 / 100 100 80 30 30 10
Sandpoint 55 42 47 30 47 31 / 100 100 90 60 50 20
Kellogg 65 39 46 30 43 30 / 60 90 100 30 70 20
Moses Lake 56 39 54 30 52 28 / 80 80 30 10 20 0
Wenatchee 53 38 52 35 51 31 / 90 60 20 10 20 0
Omak 53 40 54 28 52 30 / 80 60 20 10 10 0
&&
.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Flood Watch from 1 PM PDT this afternoon through Tuesday evening
for Northern Panhandle.
WA...Flood Watch from 1 PM PDT this afternoon through Tuesday evening
for Northeast Mountains-Okanogan Highlands.
&&The national radar mosaic for the moment the first event began.
6 flood. Local standard time, as filed.
The report received at 1300 PDT Tuesday. Washout occurred along shoulder of SR-25 at MP 44.6.
Mingo Mtn Road has washout and debris from culvert on road.
Widow Road is affected by washout and debris from heavy rain.
Culvert and washout issues on Snyder Road on Swede Pass roadway from heavy rain/snowmelt.
Runoff caused culvert problems and washout on Blue Creek and Lock roads.
Report received 1 PM PDT Tuesday of water over road at MP 149.8. Water was over both lanes of SR-21 but road still open. Creek going through a culvert was too much for culvert to handle resulting in water over roadway.
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, April 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: 1096290, 1096294, 1096295, 1096296, 1096357, 1096281.