Debris Flow and Flooding in California, January 19, 2010

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA CA
957 PM PST MON JAN 18 2010

.DISCUSSION...AS OF 8:32 PM PST MONDAY...SCATTERED SHOWERS TONIGHT.
MORE STORMS FOR THE NEXT SEVERAL DAYS.

IT WAS A BUSY DAY TODAY WITH SHOWERS AND THUNDERSTORMS OCCURRING
ACROSS THE CWA AT ONE TIME OR ANOTHER. THESE THUNDERSTORMS PACKED A
PUNCH WITH AROUND 85 LIGHTNING STRIKES(OVER THE PAST 24 HOURS)ACROSS
THE CWA AND COASTAL WATERS. A STORM RELATED WIND GUST OF 51 KNOTS AT
KSFO AND 60 KNOTS AT PILLAR POINT. THE AREA ALSO EXPERIENCED A PERIOD
OF HEAVY RAIN WHICH RESULTED IN LOCALIZED MUD AND ROCK SLIDES.

CURRENTLY THE IR SATELLITE IMAGE IS SHOWING A BREAK IN THE HEAVY
SHOWER ACTIVITY FOR THE CWA AND COASTAL WATERS. HOWEVER...ALSO
APPARENT ON THE IR SATELLITE IMAGE IS A BAND OF COLD CLOUD TOPS...
-45 TO -50 DEGREES C...LOCATED ABOUT 130 W AND HEADING TOWARDS THE
CALIFORNIA COAST. THESE COLD CLOUD TOPS ARE THE PRECURSOR TO THE
NEXT ROUND OF SHOWERS AND THUNDERSTORMS FOR THE AREA. THE LEADING
EDGE OF THIS STORM SYSTEM SHOULD BE WITHIN MONTEREY'S COASTAL WATERS
BY APPROXIMATELY 1200 UTC.

IN THE MEAN TIME CONCERNS WILL BE CONTINUED SHOWER ACTIVITY AND THE
POSSIBILITY OF AN ISOLATED THUNDERSTORM. THE CURRENT GOES SATELLITE
SOUNDER IS ESTIMATING LIFTED INDEX VALUES...IN AREAS NOT CONTAMINATED
BY CLOUDS ALONG THE COAST...TO BE 0 TO -4 DEGREES CELSIUS WHICH IS
VERY SIMILAR TO THE LATEST VALUES DERIVED BY THE 0000 UTC NAM12
MODEL. THE NAM 12 IS ALSO INDICATING SURFACE BASED CAPE VALUES
BETWEEN 620 J/KG ALONG THE SONOMA COAST TO 1000 J/KG ALONG THE
MONTEREY COASTLINE. SHEAR VALUES ARE EQUALLY AS IMPRESSIVE AND IN
SUPPORT OF THUNDERSTORM DEVELOPMENT. THEREFORE HAVE UPDATED THE
FORECAST TO INCLUDE A SLIGHT CHANCE OF THUNDER IN THE OVERNIGHT
FORECAST PERIOD.

ALSO AHEAD OF THE APPROACHING STORM SYSTEM WILL BE STRONG SOUTHERLY
WINDS REACHING 20 TO 30 MPH WITH GUSTS UP TO 50 MPH. CURRENTLY THERE
IS A WIND ADVISORY OUT FOR THE COASTAL AND MOUNTAIN ZONES THAT BEGINS
AT 900 AM TUESDAY. AFTER FURTHER ANALYSIS IT APPEARS THAT THESE
WINDS MAYBE BEGIN EARLIER SO HAVE ADJUSTED THE ADVISORY TO BEGIN BY
600 AM TUESDAY MORNING (1400 UTC).

ADDITIONALLY...HAVE ADDED A COASTAL FLOOD WATCH FOR THE ENTIRE
COAST BEGINNING 0600 UTC WEDNESDAY THROUGH 0000 UTC THURSDAY. THE
RATIONAL BEHIND THIS COASTAL FLOOD WATCH IS A COMBINATION OF
FACTORS. FIRST THE AREA HAS RECEIVED COPIOUS AMOUNTS OF RAIN TODAY
AND MORE IS EXPECTED TOMORROW. THIS WILL RESULT IN RIVERS SUCH
AS THE CARMEL...SALINAS AND RUSSIAN RIVER TO TRANSPORT THIS WATER
ALONG WITH DEBRIS INTO THE OCEAN. MEAN WHILE LARGE WIND DRIVEN
SWELL IN EXCESS OF 24 FEET IS MOVING TOWARD THE COAST WITH THE
LARGEST WAVES AND STRONGEST WINDS EXPECTED TUESDAY NIGHT INTO
WEDNESDAY. THESE FACTORS WILL RESULT IN ADDITIONAL BEACH EROSION AND
INUNDATION OF LAND AREAS ALONG THE COAST.

&&

.AVIATION...AS OF 9:55 PM...FINAL ROUND OF SHOWERS AND ISOLATED
THUNDERSTORMS WILL EXIT THE AREA AROUND 06Z. THE BREAK FROM PRECIP
AND STRONG GUSTY WINDS WILL NOT LAST LONG AS THE NEXT STRONG STORM
SYSTEM APPROACHES THE COAST LATE TONIGHT. LIGHT RAIN WILL SPREAD
ACROSS MOST OF THE REGION BY 12Z. RAINFALL WILL INTENSIFY AROUND
SUNRISE AND PERIODS OF HEAVY RAIN WILL CONTINUE THROUGH MIDDAY
TUESDAY. SOUTHERLY WINDS WILL INCREASE OVERNIGHT AND BE STRONG AND
GUSTY BY 14Z. STRONG SOUTHEAST TO SOUTH WINDS WILL CONTINUE THROUGH
MIDDAY WHEN FRONTAL PASSAGE IS EXPECTED. WINDS WILL THEN TURN TO
THE SOUTH-SOUTHWEST AND DECREASE SOMEWHAT AFTER FRONTAL PASSAGE.
SHOWERS AND POSSIBLE THUNDERSTORMS WILL CONTINUE THROUGH TUESDAY
AFTERNOON AND POSSIBLY INTO EARLY EVENING.

VICINITY OF KSFO...RAINFALL AND MFVR CIGS WILL DEVELOP BY AROUND
12Z. RAINFALL WILL BE HEAVY AT TIMES BETWEEN 15Z AND 19Z...WITH
SHOWERS TO FOLLOW DURING THE AFTERNOON HOURS OF TUESDAY. ISOLATED
THUNDERSTORMS ARE POSSIBLE IN THE AFTERNOON. SOUTHEAST WINDS WILL
INCREASE TO 25G35 KT LATE TONIGHT AND CONTINUE THROUGH TUESDAY
MORNING BEFORE TURNING TO THE SSW AND DECREASING SOMEWHAT IN THE
AFTERNOON.

KSFO BRIDGE APPROACH...SIMILAR AS KSFO.

MRY BAY AREA TERMINALS...RAINFALL AND MVFR CIGS WILL DEVELOP BY 14Z.
RAINFALL INTENSITY WILL INCREASE THROUGH TUESDAY MORNING. FRONTAL
PASSAGE WILL OCCUR AROUND MIDDAY WITH SHOWERS TO FOLLOW IN THE
AFTERNOON. SOUTHEAST WINDS WILL INCREASE THROUGH MID MORNING
TUESDAY...PARTICULARLY IN THE SALINAS VALLEY...AND THEN VEER AND
DECREASE SOME IN THE AFTERNOON.

&&

.MARINE...AS OF 9:55 PM MONDAY...GALE FORCE SE WINDS WILL DEVELOP BY
TUESDAY MORNING OVER THE COASTAL WATERS AS THE NEXT POWERFUL PACIFIC
WEATHER SYSTEM APPROACHES THE COAST. GALES WILL THEN CONTINUE UNTIL
ABOUT MIDDAY TUESDAY AND THEN WINDS WILL GRADUALLY DIMINISH IN THE
AFTERNOON AND EVENING. STRONG WINDS WILL OCCUR ONCE AGAIN ON
WEDNESDAY AND THURSDAY AS TWO MORE STRONG STORMS MOVE THROUGH THE
AREA. IN ADDITION TO THE STRONG WINDS...SEAS WILL CONTINUE TO
INCREASE TO AS HIGH AS 20 FEET BY TUESDAY MORNING...AND POSSIBLY AS
HIGH AS 25 FEET WEDNESDAY INTO THURSDAY. LOCAL BEACHES COULD SEE
SIGNIFICANT BEACH EROSION...RIP CURRENTS...AND COASTAL FLOODING.
A HIGH SURF ADVISORY AND HIGH SURF WARNING REMAIN IN EFFECT FOR
COASTAL AREAS FROM SONOMA COUNTY SOUTH THROUGH MONTEREY COUNTY. IN
ADDITION...A COASTAL FLOOD WATCH HAS BEEN POSTED FOR THESE SAME
AREAS AND IS VALID FROM LATE TUESDAY EVENING THROUGH WEDNESDAY
AFTERNOON. PLEASE SEE SFOCFWMTR WHUS46 KMTR FOR MORE INFORMATION.

TIDE INFORMATION FOR THE GOLDEN GATE...
TUESDAY MORNING 2:14 AM 5.2 FT
TUESDAY AFTERNOON 1:29 PM 4.9 FT

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .TNGT...GALE WARNING...SF BAY AND COASTAL WATERS N OF PIGEON
                            POINT.
             SCA...MONTEREY BAY AND COASTAL WATERS SOUTH OF PIGEON
                   POINT.
             SCA...SAN FRANCISCO BAR FOR ROUGH BAR
             HIGH SURF ADVISORY...ENTIRE COAST.
     .5 AM TUESDAY THROUGH 4 PM TUESDAY...WIND ADVISORY...ENTIRE
             COAST AS WELL AS THE NORTH AND EAST BAY HILLS.
     .TUE EVENING THROUGH WEDNESDAY AFTERNOON...COASTAL FLOOD WATCH
             FOR THE ENTIRE COAST

PUBLIC FORECAST: LARRY
AVIATION/MARINE: DYKEMA

NWS ON THE WEB AT WEATHER.GOV/SANFRANCISCO

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