The combination of two storm systems, one off the northern California coast and one southwest of Los Angeles, produced heavy rainfall across the central coast over January 8th to the 9th. Rain caused minor roadway flooding and a few small debris flows.
Every event with a place to put it; 1 filed by county or forecast zone are drawn at its center, in a lighter ring. 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.
The combination of two storm systems, one off the northern California coast and one southwest of Los Angeles, produced heavy rainfall across the central coast over January 8th to the 9th. Rain caused minor roadway flooding and a few small debris flows.
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 Jan 8, 3:38 AM PST, 1 hour 17 minutes earlier.
Area Forecast Discussion
National Weather Service San Francisco Bay Area
338 AM PST Mon Jan 8 2018
.SYNOPSIS...An approaching storm system is expected to be the
strongest so far this season, producing periods of heavy rain and
strong winds, especially later today and tonight. Showers will
continue into Tuesday. Dry and mild weather is forecast for the
second half of the week and into the upcoming weekend.
&&
.DISCUSSION...As of 3:20 AM PST Sunday...Light rain has been
spreading across our region since late last evening as a storm
system takes shape offshore. The system still looks rather
disorganized on IR satellite imagery. A trough offshore along
135W is digging to the SSE and is about to merge with a weaker
system farther to the south that has a subtropical moisture tap.
Models continue to forecast intensification of this system through
this evening as a closed upper low develops off the central
California coast. The models have trended towards a somewhat more
southerly track for the upper low as it approaches the coast
tonight and then moves inland somewhere near Point Conception on
Tuesday. Even with a more southerly trajectory for this system,
the models continue to indicate widespread rainfall across our
entire forecast area through tonight. The local WRF model forecasts
widespread moderate rain with pockets of heavy rain throughout our
forecast area from this afternoon into tonight. This includes the
North Bay where the WRF forecasts hourly rain rates in excess of
a half inch per hour at times. Rainfall of this intensity may
trigger debris flows and/or flash flooding in and near the North
Bay burn scars. A Flash Flood Watch is currently in effect for the
North Bay Mountains and Valleys from this afternoon through late
tonight. Most model data now indicate rain rates will begin to
decrease in the North Bay after midnight tonight, so it appears
the greatest threat of debris flows and flash flooding in the
North Bay will be from this afternoon through late this evening.
Farther south, rain rates will likely remain heavy at times
through late tonight, particularly in the Santa Lucia Mountains
above Big Sur.
Rain will transition to showers on Tuesday morning as the upper
low approaches the coast to our south. With the somewhat more
southerly trajectory now expected for this system, it now appears
that instability required for thunderstorm development will
primarily be confined to the far southern portion of our forecast
area late tonight and Tuesday, mainly across southern Monterey
County and southern San Benito County. Therefore, thunderstorm
chances have been removed entirely from the San Francisco Bay
Area.
Once the low moves inland on Tuesday it is forecast to accelerate
to the southeast. Thus, shower activity is expected to quickly end
from north to south on Tuesday evening, with little or no rainfall
likely after midnight Tuesday night.
Rainfall totals through Tuesday evening are forecast to range from
2-4 inches in the mountains, except locally up to 6 inches in the
Santa Lucias. Rainfall totals at lower elevations are expected to
generally range from 1.25 to 2.5 inches. Outside the burn scar
areas, hydro issues are not anticipated, other than the typical
nuisance flooding of low lying or poorly drained areas. Soils are
not saturated and therefore will be able to absorb significant
rainfall which in turn will mean reduced runoff.
Expect southerly winds to gradually increase through today as a
surface low deepens off our coast. Strongest winds are expected to
occur this evening. Because the surface low will be farther south
than is typical for our winter storm systems, the strongest winds
are expected across the southern portion of our area, especially
along the Big Sur Coast and in the Santa Lucia Mountains where a
High Wind Warning is in effect from Noon today through tonight. A
Wind Advisory covers much of the rest of our forecast area for the
same time period, mainly coastal and mountain locations. Latest
models do not deepen the surface low as much as previous model
runs and thus winds are not expected to reach the intensity that
was expected 24 hours ago. In any case, locally strong winds are
still expected with gusts as high as 50 mph. So will not change
the current wind warnings and advisories at this time.
Dry weather will return by Wednesday and then likely persist
through next weekend as an upper ridge builds over California. The
06Z NAM forecasts scattered light warm advection rain in the North
Bay on Wednesday, but both the GFS and ECMWF keep that rain to our
north. Temperatures are expected to gradually warm during the
second half of the week and high temperatures are forecast to
climb into the 70s across the southern portion of our area by the
weekend.
Farther out, the 00Z ECMWF forecasts a system to bring light to
moderate rain to much of our area next Monday/Tuesday while the
GFS indicates that system will mostly fall apart by the time it
reaches our area.
&&
.AVIATION...as of 03:34 AM PST Monday...12Z TAFS...Wet and at
times windy weather through much of the TAF forecast. Widespread
rain will continue to impact most terminals this morning with -RA
and vis 4-8sm. Cigs will vary greatly however, but generally AOA
1200 ft. There could be a brief break/SHRA this afternoon before
heavier rain arrives this evening and early tonight. Winds will be
gusty at times, but SNS and SJC will likely see the strongest
winds.
Vicinity of KSFO...Mix of VFR to MVFR conditions will generally
wet runways through the TAF period.
SFO Bridge Approach...Similar to KSFO.
Monterey Bay Terminals...Mix of VFR to MVFR conditions will generally
wet runways through the TAF period. Winds with gusts to 20-30kt
will be poss for SNS later today.
&&
.MARINE...as of 03:30 AM PST Monday...A potent storm system will
sweep through the region today and tonight. The passing storm will
bring increasing southerly winds today and tonight. Winds will be
strongest Monday afternoon and mainly south of Pigeon Point. Gusts
up to 50 kt will be possible along the immediate coast south of
Monterey. Winds decrease rapidly Monday night and eventually
become more northerly Tuesday. Mariners venturing to open waters
today should check the latest observations and use caution.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
.Tday...Wind Advisory...Mountains and coast of the San Francisco Bay Area as
well as interior Monterey County and San Benito County.
High Wind Warning...Big Sur Coast and Santa Lucia Mountains.
Flash Flood Watch...North Bay Mountains and Valleys (burn scar areas)
SCA...Pt Reyes to Pigeon Pt 0-10 nm from 8 AM until 3 PM
SCA...Pigeon Pt to Pt Pinos 0-10 nm from 8 AM until 3 PM
SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm from 8 AM until 3 PM
SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm from 8 AM until 3
PM
GLW...Pt Reyes to Pigeon Pt 0-10 nm from 3 PM
GLW...Pigeon Pt to Pt Pinos 0-10 nm from 3 PM
GLW...Pt Pinos to Pt Piedras Blancas 0-10 nm from 3 PM
GLW...Pigeon Pt to Pt Piedras Blancas 10-60 nm from 3 PM
SCA...Pt Arena to Pt Reyes 0-10 nm from 8 AM
SCA...Pt Arena to Pigeon Pt 10-60 nm from 8 AM
SCA...SF Bay from 3 PM
SCA...Mry Bay from 3 PM
&&
PUBLIC FORECAST: Dykema
AVIATION: MM
MARINE: MM
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www.youtube.com/nwsbayareaThe national radar mosaic for the moment the first event began.
14 flood, 3 debris flow, 1 strong wind. Local standard time, as filed.
Roadway flooding reported at 3601 Telegraph Ave. Eight inches of standing water blocking the off ramp.
Roadway flooding reported at 455 8th Street. Two inches of water across the right exit lane.
Roadway flooding reported at I 280S and Cesar Chavez Street W on ramp.
Roadway flooding reported at I 680S and Ygnacio Valley Road on ramp. Six inches of standing water.
Roadway flooding reported at intersection of Davis and Hitchcock.
Mud and rocks reported on half of the road at Empire Grade and Jamison Creek Road.
Multiple lanes flooded at US 101N and Cesar Chavez St W Onramp.
Large amount of water reported in roadway of SR1 N and Morrissey.
Roadway flooding reported at Pajaro and Haight St.
Roadway flooding reported at I280 S and 10th Street off ramp.
Roadway flooding at I 680S and Livorna Road off ramp.
Tree down on Ice Cream Grade and Winter Creek Road.
Uphill slippage reported on Redwood Road at mile marker 3.5 on the perimeter of the Nuns Fire burn scar. Exact time of occurrence is unknown.
I 680 southbound lanes flooded.
WB I80 at Macdonald, lane flooded.
Roadway flooding reported at 53 San Clemente Drive.
One inch deep slide blocking roadway at SR116 and Riverside Drive.
Roadway flooding reported at SR17 N and Hamilton Ave E on ramp. Slow lane completely flooded.
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, January 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: 729845, 729846, 729847, 729848, 729849, 730264, 730255, 730256, 730257, 730258, 730259, 730265, 730501, 730260, 730261, 730262, 730500, 730263.