Sub-tropical jet stream aided in advecting sub-tropical moisture plume from over the Central Pacific into the California Coast starting March 9th through the 11th. This led to widespread flooding around the CWA, numerous landslides, sharp rises in rivers in Monterey County, and widespread power outages from downed trees and powerlines due to strong, gusty winds.
Every event with a place to put it; 5 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.
Sub-tropical jet stream aided in advecting sub-tropical moisture plume from over the Central Pacific into the California Coast starting March 9th through the 11th. This led to widespread flooding around the CWA, numerous landslides, sharp rises in rivers in Monterey County, and widespread power outages from downed trees and powerlines due to strong, gusty winds. Widespread wind gusts 45 to 55 mph were reported on the evening of the 9th and into the early hours of the 10th. Heavy rains during the same time flooded numerous streams, creeks, rivers, and roads. 4-7 inches of rain fell across the Santa Cruz Mountains while 5-10 inches of rain fell on the Santa Lucia Mountains.
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 Mar 10, 1:16 AM UTC, 1 hour 24 minutes earlier.
Area Forecast Discussion
National Weather Service San Francisco Bay Area
516 PM PST Thu Mar 9 2023
.SYNOPSIS...An atmospheric river will continue to impact the
entire San Francisco Bay Area and Central Coast through Friday.
The main impacts will be strong winds and widespread rainfall
resulting in flooding concerns. Lingering, yet lighter
precipitation will continue into the weekend with yet another
atmospheric river arriving early next week. Folks are encouraged
to remain up to date with the latest forecast information in the
days ahead.
&&
...Atmospheric River to Impact the San Francisco Bay Area &
Central Coast through Friday with lingering precipitation over
the weekend...
.DISCUSSION...as of 12:20 PM PST Thursday...
Main Takeaways:
*A strong atmospheric river (AR) arrived this morning.
*The peak of the AR will occur this afternoon through Friday
morning, bringing widespread and prolonged rain.
*The Santa Cruz and Santa Lucia mountains continue to be the areas
of greatest concern for potential flooding impacts.
*Forecasted rainfall totals:
Inland regions: 1 to 3"
Inland hills: 3 to 6"
Santa Cruz Mountains: 4 to 6" with locally higher amounts up to 8"
Santa Lucia Range: 8 to 10" with locally higher amounts up to 12"
*Strong winds of 20 to 30 mph with gusts of 50 to 60 mph will last
through Friday morning. Downed trees and power outages will be
possible.
*Flooding remains a very high concern. Urban flooding as well as
the rapid rise of rivers and streams is expected to start this
afternoon. Elevated water levels will last into the weekend. A
Flood Watch remains in effect through Sunday afternoon.
Midlevel water vapor imagery shows the progression of the
atmospheric river across central and northern California this
afternoon. An upper low offshore of the Pacific northwest is
aiding in this due to subtropical moisture being directed across
the region. Radar indicates more widespread rainfall activity
since this morning. Additionally, stronger echoes are approaching
the coast which means heavier rain is on the way.
Models are in very good agreement with the NAM, GFS and ECMWF
regarding both timing and the strength of this AR event.
Integrated Water Vapor transport values around 1000 kg/m/s are at
the heart of this AR and look to make landfall later this
afternoon lasting into Friday afternoon. This, combined with a
strong, low-level, southerly jet around 60 knots, the steering
force driving this water vapor towards the region, will add to
the dynamics of this situation. The orientation of this jet is
perpendicular to terrain, creating an environment for upsloping
(orographic lift) that will enhance the amount of rainfall and the
potential for thunderstorms. This is why all eyes are on this
system with the hardest hit areas expected to be the Santa Cruz
and Santa Lucia mountains.
Flooding is an extremely serious concern associated with this AR.
The ground is already saturated and streams/rivers are already
swollen. When additional heavy rainfall falls on an already
saturated ground the only thing it can do is run off.
Streams/rivers will be quicker to flood due to their current
capacity. Expect the potential for areas near canyons to flash
flood, urban flooding and mainstem river flooding. Particularly
vulnerable areas include the San Lorenzo River at Big Trees, the
Pajaro Creek near Dunneville, and the Big Sur River near Big Sur.
Also, the landslide and debris flow potential is of a similar
heightened concern due to the aforementioned reasons combined with
the gusty winds. Even if the water doesn't seem deep, there's no
way to know if the road below has washed away and just how much
erosion has taken place. Turn around, don't drown!
Expect rain to transition to a more showery nature for Saturday
and Sunday as the strength of the plume of moisture lessens
significantly. Following this, another AR looks to be on the
horizon for Monday and Tuesday. It does not look to be as strong,
however, with the rain and flooding associated with the AR
currently upon us, impacts will continue to be of great extent if
this next AR is to occur. The extended forecast shows a
continuation of this active pattern for, at least, the next 10
days.
&&
.AVIATION...as of 5:15 PM PST Thursday...For the 00Z TAFs. Water
vapor imagery shows a large plume of moisture overspreading the
region, with local radar indicating rain over most of the SF Bay
Area. Echoes over Monterey Bay and the Central Coast are more
scattered. Flight rules vary from VFR to LIFR with low vsby in
RA/BR and varying cig levels. SE winds have rapidly increased and
terminals are reporting gusts 15-35 kt. Stronger gusts are
observed in hills above 1000 ft due to a strong southerly low-
level jet, reaching 50-60 kt. Thus, seeing reports of LLWS and
turbulence across the area. Models indicate strongest winds and
heaviest rain will arrive overnight, then diminish from north to
south beginning around sunrise through the afternoon, with
moisture becoming more focused over the Central Coast. Chances for
thunderstorms will also be monitored overnight and Friday
morning, as a few lightning flashes are currently detected about
600 miles off the CA coast.
Cigs will be slow to clear Friday afternoon, with best chances
north of SF Bay. Otherwise, MVFR cigs persist with lighter winds
veering to the W/NW.
Vicinity of KSFO...Prevailing MVFR at area terminals with light to
moderate rain. Winds strong and gusty out of the S/SE, with gusts
30-40kt, potentially up to 45 kt overnight, then diminishing
through the morning. LLWS and turbulence continuing through early
morning as well with strong southerly LLJ. MVFR/IFR conditions
overnight through the morning in RA/+RA. Winds veer to the SW/W
later in the morning, but timing still uncertain. MVFR Friday with
possible VFR by late afternoon or early evening.
KSFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Areas of rain with varied VFR/MVFR/IFR
conditions at area terminals. Mainly light to moderate rain
tonight, before heavier rain arrives around midnight and lasts
through the morning, with IFR/MVFR conditions. Gusty SE/S winds
will peak overnight, 35-45 kt. LLWS reported at KMRY, which may
continue overnight, until LLJ weakens by early morning. Showers
may linger through the afternoon, with MVFR conditions expected.
Winds will weaken as well.
&&
.MARINE...as of 02:37 PM PST Thursday...Expect strong southerly
winds with gale force gusts lasting through Friday morning with
the potential for occasional gusts reaching low end storm force
speeds. In addition, widespread heavy rainfall with slight chances
of thunderstorms Thursday night into Friday, along with steep,
hazardous seas are expected. Southwesterly swell will arrive and
build over the waters this weekend.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
.Tngt...Flood Watch...CAZ006-502>506-508>510-512>518-528>530
Wind Advisory...CAZ006-502>506-508>510-512>518-528>530
GLW...SF Bay
GLW...Mry Bay
GLW...Pigeon Pt to Pt Pinos 0-10 nm
GLW...Pt Pinos to Pt Piedras Blancas 0-10 nm
GLW...Pigeon Pt to Pt Piedras Blancas 10-60 nm
GLW...Pt Arena to Pt Reyes 0-10 nm until 3 AM
GLW...Pt Reyes to Pigeon Pt 0-10 nm until 3 AM
GLW...Pt Arena to Pigeon Pt 10-60 nm until 3 AM
&&
PUBLIC FORECAST: Kobold
AVIATION: Lorber
MARINE: Murdock
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www.youtube.com/nwsbayareaPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
556 PM PST THU MAR 9 2023
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0553 PM FLOOD 1 E DUBLIN 37.71N 121.88W
03/09/2023 ALAMEDA CA LAW ENFORCEMENT
ROADWAY FLOODING. MAJOR FLOODING PER REPORT.
4999 GLEASON DRIVE.
&&
ACPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
625 PM PST THU MAR 9 2023
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0617 PM FLOOD 1 NW ROSELAND 38.43N 122.74W
03/09/2023 SONOMA CA LAW ENFORCEMENT
ROADWAY FLOODING, ALL 4 LANES OF OFFRAMP ARE
FLOODED. SR12 AND STONY POINT ROAD.
&&
ACPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
626 PM PST THU MAR 9 2023
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0614 PM NON-TSTM WND DMG 1 WSW GRATON 38.44N 122.88W
03/09/2023 SONOMA CA LAW ENFORCEMENT
TREE DOWN BLOCKING ROADWAY, SULLIVAN AND
GRATON ROAD.
&&
ACPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
628 PM PST THU MAR 9 2023
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0610 PM FLOOD 4 N CALISTOGA 38.64N 122.59W
03/09/2023 NAPA CA LAW ENFORCEMENT
BOULDERS IN ROADWAY.
&&
ACPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
638 PM PST THU MAR 9 2023
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0627 PM FLOOD 8 W MONTE RIO 38.48N 123.16W
03/09/2023 SONOMA CA LAW ENFORCEMENT
MUDSLIDE BLOCKING SB LANES OF HWY 1 AT 14100
MEYERS GRADE ROAD.
&&
ACPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
639 PM PST THU MAR 9 2023
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0634 PM FLOOD 2 SE SEBASTOPOL 38.38N 122.81W
03/09/2023 SONOMA CA PUBLIC
ROADWAY FLOODING, ALL LANES COVERED IN
WATER. SR116, BLOOMFIELD ROAD.
&&
ACThe national radar mosaic for the moment the first event began.
5 flood, 4 high wind, 4 heavy rain, 1 strong wind. Local standard time, as filed.
The Road to Ranches station operated by PGE reported an 83 mph wind gust.
The Mines Tower site operated by PGE reported an 86 mph wind gust.
Trained spotter around 1 mile south of Sausalito reported a gust of 65 mph.
The Los Gatos RAWS reported a 79 mph wind gust.
Del Monte Avenue was closed between Sloat Ave and Casa Verde Rd due to downed trees and power lines, causing power outages across the Monterey Peninsula. Some areas in Del Monte Forest and Pacific Grove did not get power back on for around 2 to 3 days.
CHP reported a mud slide moving debris on California Highway 116.
A levee on the Pajaro River east of the community of Pajaro was overtopped overnight, and subsequently failed, flooding the community of Pajaro and surrounding farmland. The area was evacuated, with residents only able to return after two weeks.
CHP reported a large land slide blocking southbound lanes of US Highway 101 near the Waldo Grade.
Flooding reported on the ramp from Southbound California Highway 87 to Northbound Interstate 280, with 1 foot of water over the roadway.
The roof of a warehouse on 650 85th Ave in Oakland collapsed at 3:20 AM. A 57-year old man was struck by falling debris and died; a woman suffered a broken nose. KTVU television reported that city inspectors found that water had been ponding on the roof and drains were not properly cleaned.
The roof of a warehouse on 650 85th Ave in Oakland collapsed at 3:20 AM. A 57-year old man was struck by falling debris and died; a woman suffered a broken nose. KTVU television reported that city inspectors found that water had been ponding on the roof and drains were not properly cleaned.
US Highway 101 near Chualar flooded, causing the highway to be shut down.
North Main Street in Soquel was completely washed out near Pringle Lane, after heavy rain caused debris to block the Bates Creek culvert. A temporary repair was put into place on March 11.
US Highway 101 was shut down south of Gilroy due to flooding on the roadway.
As the offices recorded each death: direct deaths were caused by the weather itself, indirect ones by something it set in motion.
| Event | Date | Age | Sex | Where | Kind |
|---|---|---|---|---|---|
| Flood, Alameda | 2023-03-10 | 57 | Male | Permanent Structure | Direct |
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2023Every state in 2023This day in weather historyWarnings in California, March 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: 1085279, 1085278, 1085242, 1085280, 1085243, 1085239, 1085277, 1085240, 1085241, 1085264, 1166041, 1085275, 1085263, 1085274.