A strong low pressure system moving down the Pacific Coast tapped into sub-tropical moisture, bringing heavy rain and strong winds from the night of December 26th through the 27th. A wind advisory was issued for the immediate coastline and coastal mountains and East Bay Hills.
Every event with a place to put it; 8 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.
A strong low pressure system moving down the Pacific Coast tapped into sub-tropical moisture, bringing heavy rain and strong winds from the night of December 26th through the 27th. A wind advisory was issued for the immediate coastline and coastal mountains and East Bay Hills. A Flood Watch covered the same coastal areas and the North Bay valleys, and several Urban and Small Stream Flood Advisories were issued for areas under the Watch.
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 Dec 27, 6:07 AM UTC, 1 hour 23 minutes earlier.
Area Forecast Discussion
National Weather Service San Francisco Bay Area
1007 PM PST Mon Dec 26 2022
.SYNOPSIS...Strong gusty winds and periods of heavy rain will
dominate the overnight hours as a system moves across the Bay Area
and Central Coast. In addition the ocean will be fierce on Tuesday
with large breaking surf. This unsettled rainy pattern remains
around the region through the end of the year, with better chances
of another storm system after the New Years holiday.
&&
.DISCUSSION...as of 10:07 PM PST Monday...Warm frontal rain is
quickly advancing eastward across the Bay Area and north Central
Coast per KMUX radar, satellite and surface observations. The
afternoon 00z Oakland upper air sounding showed the warm frontal
temperature inversion was then based at 12,200 feet.
All ingredients are lining up for heavy rain and wind tonight and
Tuesday morning due to a warm sector out ahead of a cold front,
greatly elevated precipitable waters in the prefrontal environment
emanating from the subtropics with an extension back to vicinity
of Hawaii, i.e. a substantial subtropical tap. Preceding the cold
front, southwesterly winds will be at right angles (orthogonal) to
the coastal terrain, this wind flow greatly enhances precipitation
rates up until cold frontal passage. Then with a wind shift and
southward shift in the cold frontal boundary the heaviest rain
follows southward. A strong jet stream will also advance quickly
southeastward across our cwa Tuesday morning. Showers, some heavy,
and gusty winds lingering Tuesday afternoon and evening in the
post frontal colder air mass.
Expect rivers, streams and creeks to start responding to rainfall
overnight and Tuesday; for more information please see the hydrology
section below. A mitigating factor to rain totals is the swiftness
of the cold front forecast to move through Tuesday morning, nonetheless
still expect a soaking rain overnight and Tuesday morning.
&&
.PREV DISCUSSION...as of 1:19 PM PST Monday...Afternoon satellite
shows the potent storm system on our doorstep. At this time we
have flipped our radar from clear air mode to precipitation mode
due to echos being detected over the region. However, these echos
are only virga thus far. This is typical of an approaching warm
front. Warm frontal rain will be the first sign that we have
entered the show. Models have been consistent with warm frontal
rains impacting North Bay first this afternoon. Hires models are
showing North Bay to be the benefactor of the highest values of
warm frontal rain, however they are also showing better odds of
the measuring as far south as the Santa Cruz Mountains. If you're
driving this afternoon over the Bay Area coastal ranges, be ready
to use your wipes and light, and please drive cautiously.
The big story remains tonight with a Flood Watch and Wind Advisory
in place for the most prone places to be impacted. With the warm
front greasing the skids (especially in North Bay), the cold will
move in late this evening and through during the AM hours of
Tuesday. Winds ahead of the cold front will gust into the 40s
along the coast, into the 50s over the coastal mountain ranges,
and into the 30s for interior valley locations. Couple this with
increasing rain and we could easily see branches and whole trees
toppling, not to mention debris all over the place. The rain
itself will cause ponding of water on roadways, potential
overtopping of small creeks and streams, swelling of area rivers,
and localized flooding due to drainage capacity. Simply put, it
is going to be a mess. On the plus side, the strongest part of the
system will pass overnight while most people are not out and
about. Pure rainfall numbers for the system, as provided by WPC,
are anywhere from 1-5 inches. Lowest in rainshadowed areas and
highest in the coastal mountain ranges. It is remarkable how
consistent the deterministic and ensemble models are with this
system, and the hires model are just fine tuning what has been
seen thus far.
On the backside of the cold front we'll move out of the stable
warm sector and into a coupled convective post frontal atmosphere.
This means we'll go from steady rain to showers. Some of these
showers may manifest themselves as thunderstorms. Models are
bringing in surface CAPE during this time in the 100-200 J/kg. If
there is sufficient CIN present, convection could be capped to
solely low topped convection, which means brief isolated areas of
heavy rain. Hail does not look like an issue as the airmass aloft
remains on the "warmer" side. In other words the hail growth zone
does not look to have the instability or moisture because its up
too high. The best shot of the strongest rain will be immediately
along the frontal boundary and it provides a vertical forcing
mechanism itself. Okay, enough about that...
Showers will remain through Tuesday, clearing out for Wednesday as
a transient ridge slides across, bringing us all a day to dry out
and pick up the pieces. But there is no rest for the weary as
showers return on Thursday and linger into Friday. Another potent
cold front will drop in late Friday and Saturday, bringing another
bout of wind and rain. At this time it looks like the front will
clear the area just before midnight NYE, but not all ensemble
model member agree. Let's get through tonight and then we'll re-
focus on NYE.
For now, have your supplies ready for power outages and wet/windy
conditions. Stay safe.
&&
.AVIATION...As of 10:03 PM Monday... For the 06Z TAFs. Light to
moderate rain continues to fall over the SF Bay Area, with the
lighter rain to the south. There may be breaks in the rain before
the heavier bands come through with the main frontal system
09z-15z. Conditions vary from VFR to IFR with a combination of
BR/RA and and low cigs. Winds are mainly light to moderate but
will pick up quickly out of the south ahead of the frontal passage
overnight. Could see gusts 30-35 kt at many North Bay and Bay
Area terminals. Heavy rain will likely lower vsbys to MVFR and
periods of IFR. Cigs also will lower to MVFR/IFR/local LIFR.
Strong S-SW low level jet will bring LLWS concerns with speed and
directional shear across most of the region.
Winds should start to subside later Tuesday morning and
afternoon, but rain showers should linger through the afternoon
for SF Bay Area terminals, and into the evening around Monterey
Bay. Clouds will scatter from north to south Tuesday night with
VFR conditions returning. Areas of patchy FG will also be
possible.
Vicinity of SFO... Intermittent light rain reported at the
terminal with varying MVFR/VFR conditions. Heavier rain arrives
late tonight around 10z-12z. Southerly winds should increase over
the next few hours with gusts 30-35 kt likely after 09z. LLWS
will be a concern through ~16z with a strong S-SW LLJ. Rain and
winds diminish in intensity later Tuesday morning, but most of the
day will be wet. Winds veer to the SW and W in the afternoon.
Expect MVFR conditions to continue through much of the day, with
improvement to VFR by late afternoon or early evening as clouds
scatter and rain ends.
SFO Bridge Approach... Similar to SFO.
Monterey Bay... VFR at area terminals with occasional light rain.
Trending to MVFR/IFR tonight for area terminals with moderate to
heavy rain. Southerly winds expected to intensify overnight after
with gusts reaching 25-30 kt, potentially 35 kt after 10z. Rain
will linger through the day, but diminish in intensity by the
afternoon, along with the winds. MVFR conditions likely to prevail
through the evening.
&&
.HYDROLOGY...As of 8:10 PM PST Monday...A Flood Watch remains
in effect for all of North Bay, the San Francisco Peninsula Coast
as well as the City of San Francisco, the Santa Cruz Mountains,
the Monterey Bay, Big Sur Coast, and the Santa Lucia Mountains for
late Monday night through Tuesday.
Upcoming moderate to heavy rains late tonight into Tuesday will
cause rapid rises along area rivers, streams, and creeks. While no
mainstem river flooding is forecast at this time, mainstem rivers
will see rapid rises as well, and may exceed monitor levels. The
Carmel Lagoon will also see a rapid rise. Localized flooding is
expected, especially in low-lying or poorly drained areas, such as
freeway on- and off-ramps. Localized flooding is also expected in
areas where storm drains have not been cleared of debris. There
is also a concern for mud, rock, and debris flows.
&&
.Beaches...As of 1:10 PM PST Monday...The Beach Hazard Statement
remains in effect today through Tuesday morning as a moderate
swell (8-11' @ 15 seconds) remains in the water. This makes for
surf up to 12 to 18 feet on well exposed west facing beaches.
Heights will be lower in bays and coves. Expect increased
currents, large shorebreak on steep beaches, and farther wave
runup than usual. Extra caution is advisable.
The storm that is bringing us rain and wind late tonight into
Tuesday will be followed by building swell. This west swell will
impact all area beaches by Tuesday morning. Open ocean swells of
13 to 18 feet at 15 seconds will create very hazardous beach
conditions. Surf heights on well exposed west facing beaches will
be in the 20 to 28 foot range with strong currents, long wave
runup on beaches, potential overwashing of rock outcroppings and
jetties, and numerous beaches will be cut off at high tides.
Tuesday is NOT a safe day to be at the beach.
Never turn your back to the ocean.
&&
.MARINE...as of 08:35 PM PST Monday...Southerly winds and seas
have been steadily increasing as a strong low pressure system
passes to the north. Expect strong gales and resultant very steep
seas into the late night through early Tuesday. In the wake of
the storm large swell over 15 feet will dominate the waters.
Breaking waves over shoals may reach as high as 25 feet and will
be especially dangerous at low tide. Conditions will remain
unsettled for the remainder of the week.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
.Tngt...Wind Advisory...CAZ006-502>505-509-512-515
Flood Watch...CAZ006-509-512-529
Flood Watch...CAZ502>506
SCA...SF Bay until 3 AM
SCA...Mry Bay until 3 AM
SCA...Pigeon Pt to Pt Pinos 0-10 nm until 3 AM
SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm until 3 AM
GLW...SF Bay from 3 AM
GLW...Mry Bay from 3 AM
GLW...Pigeon Pt to Pt Pinos 0-10 nm from 3 AM
GLW...Pt Pinos to Pt Piedras Blancas 0-10 nm from 3 AM
GLW...Pt Arena to Pt Reyes 0-10 nm
GLW...Pt Reyes to Pigeon Pt 0-10 nm
GLW...Pt Arena to Pigeon Pt 10-60 nm
GLW...Pigeon Pt to Pt Piedras Blancas 10-60 nm
&&
PUBLIC FORECAST: Canepa/BFG
AVIATION: Lorber
MARINE: Lorber
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www.youtube.com/nwsbayareaThe national radar mosaic for the moment the first event began.
6 high wind, 5 flood, 2 strong wind. Local standard time, as filed.
A 70 mph gust was recorded at the PGE weather station at Cobb Ridge West.
A 74 mph gust was recorded at the PGE weather station at Road to Ranches.
A 74 mph gust was recorded at the PGE weather station at Mines Tower.
A 65 mph gust was reported at the Los Gatos RAWS.
A 76 mph gust was recorded at the PGE weather station at South Black Diamond Way.
A 70 mph gust was recorded at the PGE weather station at Wolfback Ridge.
Heavy rain and high levels on Aptos Creek led to street flooding in the Rio Del Mar neighborhood of Aptos, trapping several people in their homes.
The roof of a Big 5 Sporting Goods store in San Ramon caved in the early morning hours of the 27th after a main beam broke in the center of the store. Local officials from the San Ramon Valley Protection District stated that they believed heavy rain was a factor in the roof collapse. The collapse caused water and debris to flow into the Big 5; the Rite Aid pharmacy next door was also flooded. Nearby businesses in the shopping center were closed as a precaution.
A small tug and barge became unmoored in Monterey Bay at the Monterey Wharf. The Coast Guard brought the boat back to its mooring.
CHP reported around 1 foot of flooding on Southbound US Highway 101 near Folsom Street in the number 2 and 3 lanes.
CHP reported flooding on Northbound US Highway 101 at Chualar.
The Santa Rita Creek overflowed into the Bolsa Knolls neighborhood of Salinas, as reported by KSBW television.
A tree fell onto power lines near the intersection of Moraga and Rimrock Roads, causing Moraga Road to be closed from Sky Hy Drive (Yes, that spelling is correct.) and St Mary's Road in Lafayette.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2022Every state in 2022This day in weather historyWarnings in California, December 2022
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: 1080213, 1080208, 1080209, 1080210, 1080211, 1080212, 1079968, 1080033, 1078509, 1080480, 1080479, 1079967, 1080036.