Areal Flood Warning 2, NWS San Francisco Bay Area, CA

914 
WGUS86 KMTR 241749
FLSMTR

Flood Statement
National Weather Service San Francisco CA
1049 AM PDT Sun Oct 24 2021

CAC097-241759-
/O.CAN.KMTR.FA.W.0002.000000T0000Z-211024T1800Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Sonoma CA-
1049 AM PDT Sun Oct 24 2021

...THE URBAN AREA AND SMALL STREAM FLOOD WARNING IS CANCELLED FOR 
CENTRAL SONOMA COUNTY...

Flood warning will be expanded and extended to include area 
surrounding this warning due to continuing flooding and heavy rain.

LAT...LON 3835 12277 3847 12296 3849 12288 3846 12280
      3838 12271

$$

CW/AS

Area Forecast Discussion
National Weather Service San Francisco Bay Area
432 AM PDT Sun Oct 24 2021

.SYNOPSIS...Moderate to heavy rain in the North Bay today will
shift into the Bay Area by this afternoon. The heavy rain band
will shift over the Santa Cruz Mountains by early evening and the
Central coast tonight. In addition to heavy rain, strong southerly
winds will continue for much of today into this evening. Rain
turns to showers overnight into early Monday. Large northwest swells
arrive Monday with dangerous waves. A chance of North Bay light
rain Tuesday otherwise warming and drying trend.

&&

.DISCUSSION...as of 3:42 AM PDT Sunday...No changes to ongoing
wind advisory, flash flood watch and high surf warning. Gave
careful consideration to timing of all products and they continue
to look valid given latest trends. In general forecast remains on
track and not seeing much deviation between observations and
incoming model data. If anything though, precip is over performing
with values already around 1.25 for downtown SF. Mt Tamalpais has
reported 0.79 inches alone in the last hour with 6 hour values
overnight of 3.34 inches. Thats of course one of the wettest spots
and ideally suited for the current upslope regime with the
moisture rich AR now taking aim right over the Bay Area.

So to keep it simple the heavy rain has already arrived in the
North Bay and will be monitoring burn areas closely. The main stem
rivers have lots of capacity but will show massive rises over the
next 24 hours. If the AR stalls for even a few hours over the
Russian basin will have to monitor trends closely. Of more concern
is some of the flashier creeks out of the Russian Basin such as
Mark West and those near the base of Mt Tamalpais such as San
Anselmo and Corte Madera. Of course any clogged storm drains and
culverts will lead to rapid nuisance flooding with rain of this
magnitude. Wind advisories already underway for the North Bay and
officially start at 5 am for the heart of the Bay Area.

Models suggest the main AR will drop to around the Golden Gate by
roughly 2-3 pm this afternoon. Expect several hours of very heavy
rain to hammer the urban corridors during this time frame
including the 101/280 on the Peninsula and 880/680 in the East
Bay. Stay off the roads if at all possible today. As the AR
boundary approaches the Santa Cruz mountains the focus will then
shift to monitoring the CZU burn scar late this afternoon and
evening. Ben Lomond is a good bellwether site to monitor for the
highest rain rates in the hills. Last hour they reported 0.29 with
1 inch storm total so far. If rates approach 0.50 in 30 minutes
debris flows will be of concern. The huge fire damaged redwoods
will be challenged by the strong 50 kt winds coming in at ridge
top level so any downed trees will quickly compromise roadways in
the Santa Cruz mountains. Things will go down hill in a hurry in
the Santa Cruz mountains one we reach the afternoon hours.

By late evening and before midnight the boundary will push into
the hills of coastal Monterey county. The back edge will be abrupt
with precip ending quickly to the north. By midnight things will
have quieted down for the Bay Area while the precip will linger
overnight through about 12-15z across southern Monterey county.

Much cooler with a few showers on Monday. The main threat will
turn to the ocean as massive northwest swell from 20-30 feet will
hammer the coastline. Please give our first responders a break and
stay well back from the ocean Monday and Tuesday. High Surf
Warnings have been posted.

A weak system will pass the our north with a chance of some light
rain for the North Bay on Tuesday but amounts on the order of a
a couple tenths for coastal Sonoma county.

Looks like warm high pressure to our south will build in behind
this departing low. A return to more seasonably dry weather.

&&

.AVIATION...as of 4:32 AM PDT Sunday...For the 12z TAFs. Expect
rapidly deteoriating ceilings and visibilities to MVFR-IFR in
heavy rain and winds. Locally LIFR possible in the heaviest rain.
Strong to very strong southwest winds aloft resulting in low level
wind shear. Heaviest rain moving south later today and tonight
reaching the north Central Coast.

Vicinity of KSFO...MVFR with occasional IFR in heavy rain by early
afternoon, possibly earlier. Strong southeast winds at the surface
with strong to very strong southwest winds aloft resulting in low
level wind shear. Conditions improving by mid to late evening into
Monday morning.

KSFO Bridge Approach...Similar to KSFO.

Monterey Bay...VFR-MVFR with light rain developing this morning,
rain heavy at times later this morning through tonight. LIFR vsbys
possible in downpours.

&&

.BEACHES...as of 4:29 AM PDT Sunday...A strong, early season
storm system arrives today and will result in significantly
increased wave energy from late today into early Tuesday. This
wave energy will transition through the coastal waters from late
today into Tuesday, and peak on Monday. Swell of 16 to 24 feet at
16 to 18 seconds is forecast to arrive with the swell train as it
peaks on Monday and result in a number of coastal hazards. These
hazards include large breaking waves of 20 to 30 feet (higher at
favored break points), increased risk of strong longshore and rip
currents, increased risk of coastal erosion and minor coastal
flooding, and enhanced coastal run up concerns due to the summer
beach profiles in place. Due to the early arrival of these large
waves, many beaches are still transitioning from their summer
beach profiles and lack the features and steepness to resist
larger wave run up on coasts. This means that more of this wave
energy will have a chance to move onto the beach and overtake
individuals, potentially injuring them, or pulling them into the
cold ocean. Each year, people die at the coast due to these or
similar ocean conditions. A high surf warning for the entire coast
has been issued for this threat and is in effect from 11PM Sunday
to 11AM Tuesday, with the highest risks once again at west to
northwest facing beaches.

&&

.MARINE...as of 4:27 AM PDT Sunday...A strong storm system with
gales and heavy rain will transit southward through the waters
through today and tonight. Peak gusts will push into upper gale
force strength possibly reaching storm force strength, ie 40 to 50
kts. Strong winds will generate very steep fresh swell that is
hazardous for smaller craft vessels. In addition, this storm
system will generate a large WNW swell train that will arrive
shortly after the storm passes from tonight into early Tuesday.
Swell of 16 to 24 feet at 16 to 18 seconds will then wash ashore,
peaking Monday, and bring hazardous conditions in the surf zone
and near harbor entrances with breaking waves of 20 to 30 feet.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...Wind Advisory...CAZ516>518-528-530
             Flash Flood Watch...CAZ517
             Wind Advisory...CAZ006-508>513-529
             Flash Flood Watch...CAZ509-512
             Wind Advisory...CAZ505>507
             SCA...Mry Bay until 9 AM
             SCA...Pigeon Pt to Pt Pinos 0-10 nm until 9 AM
             GLW...Mry Bay from 9 AM
             GLW...Pigeon Pt to Pt Pinos 0-10 nm from 9 AM
             GLW...Pt Pinos to Pt Piedras Blancas 0-10 nm from 9 AM
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm until 7 AM
             GLW...Pt Arena to Pt Reyes 0-10 nm until 3 PM
             GLW...Pt Arena to Pigeon Pt 10-60 nm until 3 PM
             GLW...Pt Reyes to Pigeon Pt 0-10 nm
             GLW...Pigeon Pt to Pt Piedras Blancas 10-60 nm
             GLW...SF Bay

&&

PUBLIC FORECAST: RWW
AVIATION/MARINE: Canepa

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
703 AM PDT SUN OCT 24 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0639 AM     NON-TSTM WND DMG 1 W SEBASTOPOL          38.40N 122.85W
10/24/2021                   SONOMA             CA   LAW ENFORCEMENT

            TREE DOWN BLOCKING EASTBOUND LANE OF BODEGA
            HWY NEAR JEO SAVIO RD.

&&

SPM

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
707 AM PDT SUN OCT 24 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0646 AM     NON-TSTM WND DMG 4 WNW NAPA              38.32N 122.37W
10/24/2021                   NAPA               CA   LAW ENFORCEMENT

            LARGE TREE DOWN BLOCKING BOTH LANES ON
            PATRICK RD.

&&

SPM

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
710 AM PDT SUN OCT 24 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0708 AM     NON-TSTM WND DMG 3 W WOODSIDE            37.43N 122.31W
10/24/2021                   SAN MATEO          CA   LAW ENFORCEMENT

            TREE DOWN BLOCKING BOTH LANES. SR 35/SKYLINE
            BLVD AT KINGS MOUNTAIN RD.

&&

SPM

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
713 AM PDT SUN OCT 24 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0706 AM     NON-TSTM WND DMG 2 SE SEBASTOPOL         38.38N 122.80W
10/24/2021                   SONOMA             CA   PUBLIC

            TREE DOWN ON POWER LINES. STATE RT 116/
            GRAVENSTEIN HWY S.

&&

SPM

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
716 AM PDT SUN OCT 24 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0631 AM     NON-TSTM WND DMG 4 WSW CALISTOGA         38.55N 122.65W
10/24/2021                   SONOMA             CA   PUBLIC

            TREE DOWN IN ROADWAY. PORTER CREEK RD AT
            CALISTOGA RD.

&&

SPM

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
734 AM PDT SUN OCT 24 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0622 AM     FLOOD            1 S NAPA                38.28N 122.30W
10/24/2021                   NAPA               CA   LAW ENFORCEMENT

            STREET FLOODING ON GOLDEN GATE DR NEAR STATE
            ROUTE 121.

&&

SPM