A late season Atmospheric River impacted the area in early April. A very moist airmass made landfall across the North Bay before moving southward across the rest of the Bay Area.
Every event with a place to put it. Tap one for its entry below.
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 MTR wrote it up.
A late season Atmospheric River impacted the area in early April. A very moist airmass made landfall across the North Bay before moving southward across the rest of the Bay Area. The Oakland sounding measured record PWAT values of 1.69. The absence of large scale forcing prevent record breaking rainfall. Enough rain did fall, however, to cause minoir/nuisance flooding across much of the region. Numerous flood advisories were issued. Storm total rainfall amounts up to 7 were reported. The bulk of the impacts were felt on April 6,7.
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 San Francisco Bay Area, CA wrote its last area forecast discussion before the first event at Apr 6, 3:47 AM PST, 31 minutes earlier.
Area Forecast Discussion
National Weather Service San Francisco Bay Area
447 AM PDT Fri Apr 6 2018
.SYNOPSIS...A classic atmospheric river will impact the Bay Area
today into Saturday bringing periods of heavy rainfall and locally
gusty winds. Drying condition will develop Sunday and Monday. Rain
chances return Tuesday.
&&
.DISCUSSION...as of 02:37 AM PDT Friday...
Atmospheric River forecast remains on track. Early morning
satellite imagery clearly shows a strong sub-tropical moisture
tap with precipitable water values measuring 2+ inches. This
stream of moisture laden air will be arriving Friday afternoon
then continue to train across the region through Saturday morning.
Light rain has been falling steadily across North Bay since
Thursday bringing values of a quarter to nearly an inch. Rain
totals north of about the Dumbarton Bridge thus far have been
about a quarter inch for the core of the Bay Area, while south
have been zero to a few tenths.
Rain has been falling as a result of a weak cold front sinking
into the region from the north. This front is slowing and stalling
this morning while a shortwave is seen developing along it via
satellite. Cooling cloud tops are seen around this shortwave as it
approaches the coast, which means there is a deepening moist layer
which will likely lead to locally moderate rainfall this morning
for the early part of the commute. The main thing we are watching
this morning is where the stalling front stops and how long it
resides. Models have been shifting this point slightly farther
north over the last few runs. As the AR approaches the stalled
front will lift out to the north as a warm front. Warm frontal
rain processes will also develop in this area which are typically
underdone in model precipitation output. As such, the forecast
rainfall remains similar to the Thursday afternoon forecast,
higher than most model guidance, but nearly inline with the
Weather Prediction Center (WPC) back east.
Once the warm front lifts out the AR will move into the area and
will essentially follow the path of the lifting warm. This is why
the stalled front location is important. With the shift northward
in model data, we are looking at coastal Sonoma taking the brunt
of the rain. Some of the more aggressive models are bringing rain
totals for the entire event into the 12 inch range for portions of
Sonoma County. However, due to model uncertainty the forecast
precipitation remains spread out over much of North Bay. If the
nose of the AR slips south a bit the Mt. Tam area could see the
highest amounts of rain. For this reason the Flood Watch remains
in place for all of North Bay. Throughout the entire event North
Bay should experience widespread 2-4 inches with the mountains in
the 4-8 inch range and isolated totals in the 8-12 inch range. We
will also be watching how the orographics play a role in rain
rates. 700 mb winds are forecast to reach to around 50 kts as the
nose of the highest pwats reaches the Sonoma coast. This could be
the factor that drives storm total values upward. I have also left
the flood watch in place for the Santa Cruz Mountains to account
for orographics occurring due to the orthogonal orientation to
the incoming AR 25 to 50 kt flow in the 850-700 hPa layer.
As low pressure driving this AR into the region continues to
shift to the east, the AR will be moved toward the SE late Friday
into Saturday morning. During this time we could see some narrow
cold frontal rain bands set up, meaning some localized convection
and periods of intense rainfall. This will be the main time where
any sort of flood warning could be needed and all based on intense
rain rates.
By Saturday night into Sunday, the core of the heavy rain should
have exited the region to the east and southeast. Expect a drying
trend Sunday and Monday followed by some passing showers or light
rain midweek as system clip the area from the north.
Overall, abundant rain is expected over the next 24 hours for the
Bay Area and especially North Bay. Debris flows may become a
concern as the higher rain rates move over the burn scars.
Isolated rock falls and small areas of mudslides are likely in
steeper terrain. These issues are typical during any periods of
heavy rain. Wind is not expected to be an issue, but with buds and
leafs on trees there may be more surface area for the wind to
grab. Thus some localized power outages are possible due to downed
branches or isolated trees. An unsettled pattern remains in place
through next week.
&&
.AVIATION...As of 4:47 AM PDT Friday...For 12z Tafs. A low
confidence forecast over the next 24-30 hours as a storm system
approaches the Bay Area. KMUX radar shows steady, light to
moderate rain over much of the North Bay and Bay Area, with
surface observations showing a mixed bag of cigs across the
region. Cigs/vsby are expected to lower to IFR/LIFR through the
morning as heavier rain pushes in. Rain will continue to move
southward towards Monterey Bay terminals over the next couple of
hours, lowering cigs in the process. Cig heights will likely be
pretty erratic through the day. South/southeast winds will
continue through the afternoon, increasing this evening ahead of a
cold front that is forecast to push through north-to-south
sometime around 12Z Saturday.
Overall forecast confidence: Low (mainly due to cigs and vsby
through the day and evening)
Vicinity of KSFO...IFR/MVFR through the day with light to moderate
rain. Cigs may lower below 1000 ft this morning, but not
confident enough to include in TAF. Light to moderate rain
expected through the day, possibly heavy at times, will also
lower vsby. Breezy S/SE winds, occasionally gusty, through the
morning and afternoon, becoming SW and gusty overnight ahead of a
cold front that is forecast to pass through the terminal around
12z Saturday.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Rain gradually increases through the
morning, lowering cigs and increasing southeast winds through
Friday afternoon/evening. Cold front forecast to pass through
after 12z Saturday.
&&
.MARINE...as of 2:37 AM PDT Friday...Moderate to occasionally
strong southerly winds, along with rain, will continue today as an
atmospheric river impacts the coastal waters. A cold front is
projected to pass through the area on Saturday morning, turning
winds west or northwest behind the front. West swells will
increase and create hazardous seas through the day today, peaking
Saturday night and Sunday.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
.Tday...Flood Watch...All of North Bay and the Santa Cruz Mountains
SCA...Pt Reyes to Pigeon Pt 0-10 nm from 6 AM
SCA...Pigeon Pt to Pt Pinos 0-10 nm from 6 AM
SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm from 6 AM
SCA...Pt Arena to Pigeon Pt 10-60 nm
SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm from 12 PM
SCA...Pt Arena to Pt Reyes 0-10 nm
SCA...SF Bay from 7 AM
&&
PUBLIC FORECAST: BFG
AVIATION: BAM
MARINE: BAM
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www.youtube.com/nwsbayareaThe national radar mosaic for the moment the first event began.
36 flood, 4 debris flow. Local standard time, as filed.
Roadway flooding reported at 53 San Clemente Drive.
Roadway flooding reported on SB-87 to SB-280 connecting ramp.
Roadway flooding reported at Freestone Valley Ford Rd and Bodega Hwy.
Roadway flooding reported at 1298 High School Road. Roadway completely flooded, vehicles reportedly hydroplaning.
Roadway flooding reported at W Sierra Ave and Stony Point Rd.
Roadway flooding reported at Old Redwood Highway and Angela Dr.
Roadway flooding reported at 6100 Labath Ave. Water on both sides of road.
Roadway flooding reported at Old Redwood Highway and Mendocino Ave. NB lane is heavily flooded and the SB lane is starting to flood.
Roadway flooding reported at SR-121 and Sears Point Dr. SB lane completely flooded.
Social media photo showing roadway flooding in Pepper Road.
Roadway flooding reported at Green Valley Road and SR-116.
Roadway flooding reported at I-880 N and High Street off ramp.
Roadway flooding reported at I-80 W and Ashby Ave off ramp.
Roadway flooding reported at Bloomfield and Blucher Valley Rd. Entire roadway covered in approximately 2 feet of water.
Roadway flooding reported at Mark West Station Rd and Starr Rd.
Roadway flooding reported at I-80W and Powell Street off ramp.
Roadway flooding reported at SR-1 and Fallon Road.
Geysers road between Pine Mountain Road and Hale Ranch is closed due to a slide.
Roadway flooding at Bodega Ave and Valley Ford Road.
Roadway flooding reported at I-80W and Harrison St off ramp.
West Railroad Ave closed near Cypress Ave due to flooding.
Roadway flooding reported at Sexton Road and Bodega Highway.
Roadway flooding reported at Brookside Rd and W Agua Caliente Rd.
Bodega Highway at Salmon Creek closed due to flooding.
Roadway flooding reported at Canfield Rd and Schaeffer Rd.
Roadway flooding reported at I-980 E and I-580 W connecting.
Roadway flooding reported at Joy Rd and Bodega Highway.
Roadway flooding at I-580 W and I-80 E.
Roadway flooding at Valley Ford Road and Bloomfield Road.
Mudslide reported at US-101 N and Railroad Ave.
Mud blocking lanes at SR-1 and Bay Hill Road.
I-80 at 7th St in San Francisco, all lanes flooded, 1.5 feet deep.
I-80 E adjacent to the Pomona on ramp, 2 feet of water in number 1 lane.
Flooding at 6th St on ramp to I-280 S 8 to 10 inches of water in number 1 and 2 lanes.
NB 880 just south of exit 12-A Mission Blvd, 5 inches of water in HOV lane.
SB 101 just north of Ralston Ave 3 inches of water in 1 lane.
US 101 at 3rd Ave on ramp, severe flooding in 1 lane.
US 101 N at Alemany Blvd off ramp, number 1 lane flooded 6 to 8 inches deep.
US 101 NB at SFO large flooding number 1 lane.
California Highway Patrol reporting mud/dirt/rocks covering northbound Highway 1 near Anderson Canyon.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2018Every state in 2018This day in weather historyWarnings in California, April 2018
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: 744319, 744320, 744321, 744323, 744324, 744332, 744334, 744335, 744339, 744343, 744344, 744345, 744346, 744348, 744487, 744488, 744489, 744540, 744490, 744491, 744492, 744493, 744494, 744495, 744496, 744497, 744498, 744499, 744500, 744542, 744543, 744502, 744503, 744505, 744507, 744509, 744513, 744537, 744538, 744681.