A convergence zone caused heavy rain and flash flooding in Snohomish county, near Marysville and Lake Stevens.
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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 SEW wrote it up.
A convergence zone caused heavy rain and flash flooding in Snohomish county, near Marysville and Lake Stevens.
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 Seattle, WA wrote its last area forecast discussion before the first event at Apr 19, 8:00 PM PST, 4 hours earlier.
Area Forecast Discussion
National Weather Service Seattle WA
900 PM PDT Wed Apr 19 2017
.SYNOPSIS...An upper level trough will bring showers and a slight
chance of thunderstorms on Thursday. An upper level ridge will bring
sunny and warmer weather Friday. The break in the weather will be
brief with weak systems arriving Saturday and Sunday, and a stronger
system around Monday. The weather will remain wet and unsettled next
week.
&&
.SHORT TERM...An upper level short wave and main frontal band is
pushing into Wrn Washington this evening. Radar and obs indicate a
band of moderate to heavy showers near the coast earlier have pushed
inland with rain increasing over the interior, especially across
greater Puget Sound and the southwest interior. Brief heavy rain
with up to a quarter inch per hour and wind gusts up to 30 mph were
observed earlier at the coast. Similar conditions could occur
over parts of the interior for the next hour or two. The threat of
thunderstorms has likely ended for tonight and showers should
decrease and generally end after midnight.
The main 500 mb low center will open up as the negative tilt trough
axis reaches the coast Thursday morning. Some uptick in showers are
expected due to increased instability as the -30C cold pool at 500mb
reaches the area. Diurnal instability will drive most the low
topped shower activity by afternoon with the main trough axis and
dynamics shifting east of the Cascades. Thunderstorms will probably
not be widespread due to the early timing of the trough axis with
most activity near the coast and southwest interior. A few strikes
could also occur late in the day over the rest of the interior as
lapse rates steepen. Showers and thunderstorms will end by sunset
Thursday evening as the air mass rapidly stabilizes.
Models still show high pressure aloft rapidly building over the
region later Thursday night and Friday. Upper heights near 5700m
suggest widespread highs in the low to mid 60s, with a couple spots
inland from the water possibly hitting the 70 mark. It will be dry
and mostly sunny.
Another system will arrive Saturday but looks to be rather weak.
Expect some spotty light rain, especially by afternoon. Highs will
be tricky depending on the timing of the rain and track of the upper
low. Some models show more south-southeast flow at 700mb and
diffluence over the area which could provide sufficient lift for
some thunderstorms, especially over the Cascades. Will need to
evaluate this for the next forecast issuance late tonight/early
Thursday morning. Mercer
.LONG TERM..Previous discussion...The upper level low will move
through Western Washington Sunday, keeping showers likely. A more
consolidated front will reach the area Monday or Monday night. A
broad upper level trough will move over the area on Tuesday, with
moist westerly flow aloft Wednesday. Both these patterns will keep a
chance of showers in the forecast. Highs will be mostly in the 50s
Sunday through Wednesday. Models have been unusually consistent
about this sequence of events. Burke
&&
.AVIATION...A band of showers with breezy weather is moving through
Western Washington this evening, a little after 6pm the wind gusted
above 30mph with heavy showers at Hoquiam and around 8pm the same
thing happened at Shelton. Those showers will continue to move north
through the Seattle metro area around 9pm. Then, overnight, showers
will give out but areas of stratus should develop. Morning clouds
Thursday should give way to afternoon cumulus.
KSEA...Showers will be moving through Seattle by about 9pm, the TAF
has those in the forecast. Thursday should see morning clouds give
way to sct-bkn cumulus in the afternoon. Winds will remain southerly.
&&
.MARINE...A weather disturbance moved through the coastal waters
this evening with some heavy showers and breezy southerly winds. The
showers were moving into Puget Sound around 8pm. After this system
moves through the area overnight, high pressure will build into the
area from the south through Thursday--giving a southerly breeze.
The flow will become light Thursday night, and then
easterly/offshore on Friday in response to to falling pressure over
the offshore waters.
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small craft advisory coastal waters and east entrance Strait of
Juan de Fuca.
&&
www.weather.gov/seattle
An illustrated version of this forecast discussion can be seen at
www.weather.gov/seattle/gafd/latest_webafd.htmlThe Seattle radar (KATX), 34 km away, was scanning. The volume nearest the first event began at 07:58 UTC.
1 flash flood. Local standard time, as filed.
Heavy rain caused a Flash Flood in Marysville, washing out Heineck Farms.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Washington in 2017Every state in 2017This day in weather historyWarnings in Washington, April 2017
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: 688866.