Special Weather Statement, NWS San Francisco Bay Area, CA

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1043 AM PST Wed Mar 10 2021

.SYNOPSIS...Numerous showers and isolated thunderstorms will
continue today into this evening producing brief heavy downpours
and small hail. Showers will end by early Thursday morning for
the Bay Area but linger across the Central Coast into Thursday.
High pressure builds Friday and Saturday with some dry northerly
winds bringing a warming trend with mostly clear skies. Next
chance of rain arrives Sunday into early Monday as the next trough
approaches Northern California.

&&

.DISCUSSION...as of 09:20 AM PST Wednesday...After an active
night, there's much to report this morning. As the sun rose, we
saw from webcams that snow had fallen over our higher peaks
(potentially a couple of inches) with lighter snow amounts around
2500 ft. Daylight has also revealed that there have been some
small mudslides along Chualar River Rd off Hwy 101 southeast of
Salinas. A more notable mudslide occurred on Pine Canyon Rd in
Salinas...the same place that had a mudslide off the River Fire
burn scar this past January. And we're still getting reports of
small hail with some of these showers moving inland.

Bottom line: be prepared for shower and possible thunderstorm
activity today into this evening, we're concerned about
additional soil movement around the River Fire burn scar
(primarily the eastern side), small hail can quickly cause
driving hazards, and take shelter if you hear thunder to stay safe
from lightning.

&&

.PREV DISCUSSION...as of 3:44 AM PST Wednesday...Showers and isolated
thunderstorms have continued overnight and this trend will
continue through today into this evening. Have already received
reports of small hail overnight with convective cells as they move
onshore. The coldest air aloft is still offshore but will
approach the Bay Area today. Over the last hour or so we've seen
several lightning strikes over the ocean waters from the Monterey
peninsula southward to Big Sur. As this band moves onshore expect
more small hail, brief heavy downpours and some lightning
flashes.

The core of the upper low is west of Cape Mendocino and will
slowly wobble towards the Golden Gate today but is progged to
remain just offshore and over the ocean. 700 mb temps are down to
around -14 celsius with good ice growth in the clouds along with
steep lapse rates aloft given the dynamic upper low. All this to
say is we can expect numerous showers and isolated t-storms
through the day and into this evening. Daytime heating is almost
inconsequential but of course can give a little added lift.
Nonetheless given the slow movement of the upper low expect
showers to last through around midnight for the Bay Area with
showers continuing for the Central Coast right into Thursday
morning. Some of the noted weather impacts we will be monitoring
the next 24 hours include: hail that can quickly cover roadways,
heavy downpours over 2020 burn areas and low elevation snows.

The 12z sounding that is still lifting off showed the freezing
level around 875 mb but were seeing snow levels down to around
2000-2500 feet today in heavier showers as the coldest air aloft
passes overhead. In general this should remain above most Bay Area
roadways but we could get some reports along Highway 9 and Skyline
Blvd as well as Highway 29 heading out of Calistoga. More
significant snowfall accumulations will be possible over the
higher terrain of Monterey County as well, especially with showers
lingering right into Thursday. Well most of the region will dry
out on Thursday the instability with the upper low will allow
plenty of afternoon cumulus with some showers Thursday afternoon
for the higher terrain from Mt Hamilton southward into San Benito
county as well as the Santa Cruz mtns and Santa Lucia range.

As the low drops south and east by Friday high pressure will nose
over the region. Circulation around the low will generate some
drying northeast winds across the Bay Area. This will bring a
noted warming trend Friday afternoon, especially for the North Bay
as temps warm into the upper 60s (it'll feel warm after low to mid
50s today). Dry and mild weather Saturday.

Models coming into better agreement for some more light rain
chances Sunday into early Monday with NBM PoPs in the 40-50% range
and nearly all mid range models converging on the idea of a light
to moderate strength wx system.

No clear signals for next week with pattern remaining active
enough to keep some rain chances in the forecast later next week.
No signal for any strong systems but no strong ridge forecast
either.

&&

.AVIATION...as of 10:37 AM PST Wednesday...For the 18Z TAFs. A
cold pool of air aloft with an upper level low continuing to
result in showers and isolated thunderstorms. Convection easing
from mid afternoon through evening. Expect VFR except temporarily
MVFR in showers and isolated thunderstorms.

Vicinity of KSFO...VFR to MVFR in showers and isolated thunderstorms
into mid to late afternoon. A wind shift to west to southwest occurred
according to recent 5 minute observations. Southwest wind gusts to
20 knots through late morning and afternoon.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR to MVFR in showers and isolated
thunderstorms into mid to late afternoon. Wind gusts to 20 knots
possible near thunderstorms.

&&

.MARINE...as of 10:43 AM PST Wednesday...Scattered showers
persisting with isolated thunderstorms and small hail today. Gusty
winds possible with isolated thunderstorms.  Otherwise expect
steep fresh seas with hazardous conditions for smaller craft
vessels. Winds remain out of the west-southwest and breezy,
expecting to shift to the northwest by this afternoon.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Reyes to Pigeon Pt 0-10 nm
             SCA...Pigeon Pt to Pt Pinos 0-10 nm
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm

&&

PUBLIC FORECAST: Bingaman/RW
AVIATION: Canepa
MARINE: Canepa

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
1033 AM PST WED MAR 10 2021

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

0400 AM     FLOOD            8 WNW GONZALES          36.56N 121.56W
03/10/2021                   MONTEREY           CA   PUBLIC

            REPORTS OF 1.5 FEET OF MUD INTO HOMES IN THE
            EXACT SAME PLACE AS THE LAST AR EVENT.
            RESIDENCES WERE NOT OCCUPIED AS THEY HAVE
            BEEN EVACUATED SINCE THE JAN 26-28TH AR
            EVENT.

&&

CW

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
1034 AM PST WED MAR 10 2021

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

0632 AM     FLOOD            2 W PIEDMONT            37.82N 122.27W
03/10/2021                   ALAMEDA            CA   LAW ENFORCEMENT

            ROADWAY FLOODING AT 3601 TELEGRAPH AVE.

&&

CW

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
1039 AM PST WED MAR 10 2021

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

0808 AM     FLOOD            3 WNW SAN JOSE          37.32N 121.89W
03/10/2021                   SANTA CLARA        CA   LAW ENFORCEMENT

            NB 280 JSO 87 #1 LANE.

&&

CW

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
1045 AM PST WED MAR 10 2021

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

0808 AM     FLOOD            2 SW EAST FOOTHILLS     37.36N 121.84W
03/10/2021                   SANTA CLARA        CA   LAW ENFORCEMENT

            SB 680 ON ALUM ROCK OFR.

&&

CW

Special Weather Statement
National Weather Service San Francisco CA
1136 AM PST Wed Mar 10 2021

CAZ508-513-102015-
Santa Clara Valley Including San Jose CA-
San Francisco Bay Shoreline CA-
1136 AM PST Wed Mar 10 2021

...SIGNIFICANT WEATHER ADVISORY FOR NORTH CENTRAL SANTA CLARA COUNTY
UNTIL 1215 PM PST...

At 1135 AM PST, Doppler radar was tracking a strong thunderstorm near
Milpitas, moving northeast at 10 mph.

Pea to dime size hail will be possible with this storm.

Locations impacted include...
San Jose, Fremont, Sunnyvale, Santa Clara, Milpitas, Alum Rock and
East Foothills.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

&&

LAT...LON 3752 12190 3751 12189 3748 12189 3745 12185
      3743 12186 3737 12179 3733 12195 3744 12201
TIME...MOT...LOC 1935Z 244DEG 8KT 3742 12195

BB