Flash Flood Warning 20, NWS San Francisco Bay Area, CA

Area Forecast Discussion
National Weather Service San Francisco Bay Area
357 PM PST Thu Dec 15 2016

...Locally heavy rainfall along with strong and gusty winds to
impact the region through late this evening...

.SYNOPSIS...A potent storm system will continue to impact the region
through late this evening. Locally heavy rainfall along with strong
and gusty winds will be likely as a cold front slowly pushes across
the region. Drying conditions will return to much of the region on
Friday followed by much colder overnight/early morning temperatures
through the weekend. Mainly dry weather conditions and near seasonal
temperatures appear likely for next week.

&&

.DISCUSSION...as of 1:56 PM PST Thursday...A potent weather
system continues to impact the region this afternoon with a
frontal boundary very slowly moving through the North Bay region
at this hour. This is where the heaviest rainfall is occuring with
rainfall rates upwards of 0.50" per hour reported at times. This
has resulted in widespread urban and small stream flooding as well
as rapid rises on area creeks/streams. Expecting this activity to
persist through the afternoon and slowly shift southward through
the late afternoon and evening. Meanwhile, light to moderate rain
continues to develop out ahead of the main cold front as a deep
plume of moisture with PWAT values estimated at 1.40"-1.50"
advects toward the region.

As mentioned earlier, the cold front is forecast to progress slowly
southward into the San Francisco Bay Area through the afternoon and
will likely peak in intensity during the afternoon/evening rush hour
commute. As the front approaches Santa Cruz Mountains and Central
Coast, rainfall intensity will likely increase as a shortwave
disturbances meets up with the frontal boundary and deeper plume of
moisture advection. This is when we could see rainfall rates
increase to 0.75" to 1.00" per hour at times across the coastal
slopes. This would be of concern to the recent burn scar areas as
these rainfall rates could trigger debris flows, mudslides and/or
rockslides and localized flash flooding. With this, the Flash Flood
Watch remains in effect for the Santa Cruz and Santa Lucia Mountains
through late tonight. When all said and done, southwest facing
slopes could pick up 4.00" to 6.00" of rainfall with most of that
occuring in the late afternoon and evening during a 3 to 6 hour
window of time. Urban areas will likely see 0.25" to 1.50" outside
the North Bay where storm total rainfall amounts in the valleys will
be in the 2.00" to 4.00" range.

Once the boundary clears, drying conditions will develop from north
to south late tonight into early Friday morning. Lingering moisture
and instability will allow for some showers across portions of the
region and off of the coast on Friday during the day. However, areas
most likely to see isolated showers will be across the Central
Coast. In addition, by Friday night, a colder and drier air mass
will settle into the region along with clearing skies. This will
result in much colder temperatures region-wide with overnight lows
this weekend dropping into the 30s for most areas away from the
immediate coast/bays. May even see some upper 20s in the coldest
inland, wind sheltered locations.

Mainly dry weather conditions will then persist for much of next
week with temperatures rebounding back to near seasonal averages as
a weak ridge of high pressure builds in over the region. While a few
systems pass inland to our north by the middle of next week, most of
the region is forecast to remain dry at this time.

&&

.AVIATION...As of 3:57 PM PST Thursday...For 00z tafs. Front is
moving through the bay area at this time with moderate to heavy
rain and strong south winds. Conditions wont improve much until
after 05z for bay area terminals and later for monterey bay
region.

Vicinity of KSFO...Rain and low cigs to continue this evening with
ifr conditions. Strong southerly winds at least through 05z before
wind shift to nw overnight as rain ends. Should be vfr to start
the day Friday

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...Front reaching monterey bay region at this time.
Rain, wind and low clouds to impact terminals through at least 08z
tonight. Expect vfr to start the day Friday.

&&

.MARINE...as of 03:44 PM PST Thursday...Moderate southerly winds
across our region will switch to northwesterly and slightly
diminish as a front passes through our region. look for continued
steep wind waves and fresh swell into the evening.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...Wind Advisory...CAZ508-509-511-512 until 7 am
             Wind Advisory...CAZ517-518-530 until 10 pm
             Wind Advisory...CAZ505-507 until 1 am Friday
             Flash Flood Watch...CAZ512-517 until 11 pm
             Flash Flood Watch...CAZ506 until 6 pm
             GLW...Mry Bay until 9 PM
             GLW...Pt Reyes to Pigeon Pt 0-10 nm until 9 PM
             GLW...Pigeon Pt to Pt Pinos 0-10 nm until 9 PM
             GLW...Pt Pinos to Pt Piedras Blancas 0-10 nm until 9 PM
             GLW...Pigeon Pt to Pt Piedras Blancas 10-60 nm until 9 PM
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...SF Bay until 2 AM

&&

PUBLIC FORECAST: RGass
AVIATION: RWW
MARINE: Bell

Visit us at www.weather.gov/sanfrancisco

Follow us on Facebook and twitter at:
www.Facebook.com/nwsbayarea
www.twitter.com/nwsbayarea

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
452 PM PST THU DEC 15 2016

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

0444 PM     FLASH FLOOD      2 E SCOTTS VALLEY       37.05N 121.98W
12/15/2016                   SANTA CRUZ         CA   LAW ENFORCEMENT

            ROADWAY FLOODING NEAR 97 MOUNTAIN VIEW RD

&&

DPETERSO

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
453 PM PST THU DEC 15 2016

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

0450 PM     FLASH FLOOD      3 NNW BERKELEY          37.91N 122.32W
12/15/2016                   CONTRA COSTA       CA   LAW ENFORCEMENT

            ROADWAY FLOODING I80W NEAR CARLSON BLVD RAMP

&&

DPETERSO

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
506 PM PST THU DEC 15 2016

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

0503 PM     FLASH FLOOD      1 WNW OAKLAND           37.78N 122.24W
12/15/2016                   ALAMEDA            CA   LAW ENFORCEMENT

            2 FEET OF STANDING WATER AT THE I880N 29TH AVE RAMP

&&

DPETERSO

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
513 PM PST THU DEC 15 2016

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

0504 PM     DEBRIS FLOW      3 E BEN LOMOND          37.10N 122.03W
12/15/2016                   SANTA CRUZ         CA   LAW ENFORCEMENT

            ZAYANTE RD IS COMPLETELY BLOCKED BY A MUD SLIDE

&&

DPETERSO

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
518 PM PST THU DEC 15 2016

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

0514 PM     NON-TSTM WND DMG SSW BEN LOMOND          37.10N 122.09W
12/15/2016                   SANTA CRUZ         CA   INSURANCE CO

            LARGE TREE BLOCKING ENTIRE ROADWAY AT VICINITY OF
            VINELAND RD / LOVE CREEK RD

&&

DPETERSO

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
519 PM PST THU DEC 15 2016

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

0509 PM     FLASH FLOOD      10 WSW LA HONDA RAWS    37.24N 122.42W
12/15/2016                   SAN MATEO          CA   LAW ENFORCEMENT

            ROADWAY FLOODING AT HIGHWAY 1 NEAR BEAN HOLLOW NORTH

&&

DPETERSO