Flash Flood Warning 4, NWS San Francisco Bay Area, CA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
930 AM PDT TUE APR 11 2006

.DISCUSSION...DEEP UPPER LOW IS CENTERED NEAR 38N/132W THIS MORNING
AND SATELLITE INDICATES IT IS DRIFTING SLOWLY TO THE SE. WARM
ADVECTION PRECIP DEVELOPED OVER REGION OVERNIGHT...BUT THUS FAR
RAINFALL AMOUNTS HAVE MOSTLY BEEN LIGHT WITH GENERALLY A QUARTER
INCH OR LESS ACCUMULATING SINCE LAST EVENING. A PERIOD OF HEAVIER
RAINFALL IN THE SANTA CRUZ MOUNTAINS LAST NIGHT RESULTED IN NEARLY
THREE-QUARTERS OF AN INCH OF RAINFALL THERE. RAINFALL WILL INTENSIFY
OVER THE NEXT FEW HOURS...ESPECIALLY IN THE N BAY...AS A STRONG JET
ROUNDING THE BASE OF THE UPPER TROUGH OFFSHORE ARRIVES OVER CENTRAL
CA. THIS JET WILL ENHANCE LIFT ALONG THE FRONTAL BOUNDARY AND THIS
ENHANCED LIFT CAN ALREADY BE SEEN ON IR SATELLITE IMAGERY WITH A BAND
OF RAPIDLY COOLING CLOUD TOPS JUST NOW BEGINNING TO PUSH INTO THE N
BAY. MT VACA RADAR SHOWS HEAVIER CELLS EMBEDDED IN THIS RAIN BAND AND
EXPECT MODERATE TO LOCALLY HEAVY RAIN TO SPREAD ACROSS MOST OF THE
NORTH BAY BY LATE MORNING. WITH THE LOW CENTER FORECAST TO DRIFT
SLIGHTLY FARTHER TO THE SOUTHEAST TODAY...THE BAND OF HEAVIER PRECIP
WILL MOST LIKELY SHIFT SLOWLY S THROUGH THE DAY AND RAIN RATES ALONG
THE SAN MATEO PENINSULA S TO THE SANTA CRUZ MOUNTAINS WILL PICK UP BY
LATE AFTERNOON. THEN...AS THE LOW BEGINS TO DROP DUE S TONIGHT...THE
FLOW ALOFT IS FORECAST TO VEER FROM FROM SW TO SSW WHICH WOULD SHIFT
THE HEAVIER RAIN BAND BACK TO THE N OVERNIGHT. THE PRIMARY CONCERN
OVER THE NEXT 24 HOURS IS THE POSSIBILITY OF MODERATE TO HEAVY RAIN
RATES PERSISTING OVER AN AREA FOR AN EXTENDED PERIOD OF TIME. GIVEN
THE UNFOLDING SITUATION...THAT CERTAINLY APPEARS POSSIBLE. THE
AREAS OF GREATEST CONCERN ARE FROM THE N BAY S TO THE SANTA CRUZ
MOUNTAINS. GIVEN THE VERY SATURATED SOIL CONDITIONS...A PROLONGED
PERIOD OF MODERATE TO LOCALLY HEAVY RAIN COULD VERY WELL PUSH SMALL
STREAMS AND CREEKS TO BANKFULL AND ALSO PRODUCE URBAN FLOODING. A
FLOOD WATCH IS IN EFFECT FOR THE NORTH BAY COUNTIES...THE SF
PENINSULA...AND THE SANTA CRUZ MOUNTAINS UNTIL MIDDAY WEDNESDAY.
CURRENT RAINFALL PROJECTIONS THROUGH MIDDAY WEDNESDAY RANGE FROM
1.5 TO 3 INCHES IN THE N BAY (AND LOCALLY UP TO 4 INCHES)...1 TO 2
INCHES FOR THE REST OF THE BAY AREA (LOCALLY UP TO 3 INCHES IN THE
SANTA CRUZ MOUNTAINS) AND FROM A QUARTER INCH TO AN INCH AND A HALF
ACROSS MONTEREY AND SAN BENITO COUNTIES. THESE RAINFALL AMOUNTS WILL
PRODUCE SHARP RISES ON THE MAINSTEM RIVERS...PARTICULARLY THE N
BAY...BUT ARE NOT PRESENTLY CONSIDERED SUFFICIENT TO BRING THE MAIN
STEMS TO FLOOD STAGE.

SE WINDS HAVE PICKED UP OVER THE COASTAL WATERS AND LOCALLY IN THE
HILLS WHERE SOME GUSTS AS HIGH AS 40 MPH HAVE BEEN OBSERVED. MODEL
DATA INDICATE THE SURFACE LOW HAS PROBABLY REACHED ITS MAXIMUM
DEPTH AND WILL BEGIN TO SLOWLY FILL AFTER THIS POINT. HOWEVER...THE
SURFACE LOW WILL DRIFT A BIT CLOSER TO THE COAST TODAY AND GRADIENTS
ARE EXPECTED TO REMAIN STEEP ENOUGH FOR LOCALLY STRONG AND GUSTY
WINDS THROUGH THE DAY...BUT PROBABLY NOT STRONG ENOUGH OR WIDESPREAD
ENOUGH FOR A WIND ADVISORY.

RAIN WILL TAPER OFF WEDNESDAY AFTERNOON AS THE LOW CONTINUES TO
DROP S ALONG 130W. ONLY SCATTERED SHOWERS ARE EXPECTED FROM LATE
WEDNESDAY INTO EARLY THURSDAY. AND MOSTLY DRY WEATHER IS EXPECTED FOR
MOST OF THURSDAY. BY THURSDAY NIGHT...THE LOW IS FORECAST TO MOVE
RAPIDLY TO THE ENE AND MOVE INLAND OVER SRN CA BY MIDDAY FRIDAY. AS
THE LOW MOVES TOWARD THE COAST THURSDAY NIGHT...RAINFALL WILL
REDEVELOP OVER OUR FORECAST AREA...BUT MAINLY OVER THE SOUTHERNMOST
COUNTIES. RAIN COULD BE HEAVY FOR A TIME OVER THE SANTA LUCIA
MOUNTAINS LATE THURSDAY NIGHT AND FRIDAY MORNING...BUT THE SYSTEM IS
PROJECTED TO MOVE QUICKLY BY THAT TIME AND A PROLONGED PERIOD OF
HEAVY RAIN IS NOT EXPECTED.

MODELS FORECAST THE NEXT SYSTEM TO SPREAD RAIN SLOWLY S THROUGH
NORTHERN CA LATE SATURDAY THROUGH SUNDAY...AND FINALLY INTO CENTRAL
CA BY SUNDAY NIGHT. RAINFALL AMOUNTS WITH THAT SYSTEM ARE FORECAST
TO BE HEAVIEST FROM ABOUT I-80 NORTHWARD.

&&

.AVIATION...A VERY MOIST LOW PRESSURE SYSTEM CENTERED 450 NM WEST OF
POINT REYES WILL DRENCH THE AREA TODAY BRINGING PERIODS OF HEAVY
RAIN...DECREASED VISIBILITIES AND LOWERED CEILINGS (WITHIN MVFR AND
IFR CATEGORIES). MODERATE AND GUSTY SOUTH TO SOUTHEAST WINDS WILL
CONTINUE THROUGH MOST OF THE DAY EASING LATER THIS AFTERNOON AND
TONIGHT AS THE SYSTEM MOVES SOUTHWARD.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...TDA
     .FLOOD WATCH THROUGH WEDNESDAY MORNING FOR THE
      NORTH BAY...SAN MATEO COUNTY...AND THE SANTA CRUZ MOUNTAINS.
     .SCA FROM PT ARENA TO PT PIEDRAS BLANCAS.

PUBLIC FORECAST: DYKEMA
MARINE/AVIATION: C WALBRUN

NWS ON THE WEB AT WEATHER.GOV/SANFRANCISCO

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
145 PM PDT TUE APR 11 2006

CAZ006-505>514-121300-
SAN FRANCISCO-
COASTAL NORTH BAY INCLUDING POINT REYES NATIONAL SEASHORE-
NORTH BAY INTERIOR VALLEYS-NORTH BAY MOUNTAINS-
SAN FRANCISCO BAY SHORELINE-EAST BAY INTERIOR VALLEYS-
SAN FRANCISCO PENINSULA COAST-EAST BAY HILLS AND THE DIABLO RANGE-
SANTA CRUZ MOUNTAINS-SANTA CLARA VALLEY INCLUDING SAN JOSE-
MONTEREY BAY/NORTHERN SALINAS VALLEY/HOLLISTER VALLEY AND CARMEL
VALLEY-
145 PM PDT TUE APR 11 2006

THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE SAN FRANCISCO BAY AREA AS
WELL AS THE COASTAL AREAS AROUND MONTEREY BAY AND THE NORTHERN
SALINAS VALLEY.

.DAY ONE...TUESDAY AND TUESDAY NIGHT

A STRONG STORM IS FORECAST TO MOVE SOUTH OFF THE CALIFORNIA COAST
TUESDAY AND TUESDAY NIGHT. WIDESPREAD MODERATE TO HEAVY RAIN IS
FORECAST TO SPREAD ACROSS THE REGION TUESDAY AND CONTINUE TUESDAY
NIGHT INTO WEDNESDAY MORNING. THE GREATEST RAINFALL AMOUNTS ARE
PROJECTED TO FALL OVER THE NORTH BAY MOUNTAINS...SAN MATEO COASTAL
HILLS...AND THE SANTA CRUZ MOUNTAINS. WITH THE GROUND ALREADY
SATURATED...EVEN A SHORT PERIOD OF HEAVY RAINFALL WILL RESULT IN
RAPID RISES ON SMALLER STREAMS AND CREEKS...POSSIBLY PUSHING THEM TO
BANKFULL. IN ADDITION...MORE RAINFALL ON SATURATED SOILS COULD RESULT
IN MUDSLIDE AND DEBRIS FLOWS IN AREAS OF STEEP TERRAIN.

A FLOOD WATCH IS IN EFFECT THROUGH WEDNESDAY MORNING FOR ALL NORTH
BAY COUNTIES...SAN MATEO COUNTY...AND THE SANTA CRUZ MOUNTAINS.

* FLOOD WATCH..........SEE WGUS66 KMTR - SFOFFAMTR FOR DETAILS *

AN URBAN AND SMALL STREAM FLOOD ADVISORY IS IN EFFECT FOR ALL COASTAL
COUNTIES FROM SONOMA COUNTY SOUTH THROUGH SANTA CRUZ COUNTY FOR
TUESDAY AFTERNOON AND EVENING.

* URBAN AND SMALL STREAM FLOOD ADVISORY...SEE WGUS86 KMTR -
SFOFLSMTR FOR DETAILS *

STRONG SOUTHEAST WINDS HAD DEVELOPED ACROSS THE SAN FRANCISCO BAY
AREA BY MIDDAY TUESDAY...AS WELL AS THE NORTHERN SALINAS VALLEY. A
WIND ADVISORY IS IN EFFECT FOR COASTAL AREAS AND HIGHER ELEVATIONS OF
THE SAN FRANCISCO BAY AREA AND THE SALINAS VALLEY UNTIL 11 PM TUESDAY
EVENING.

* WIND ADVISORY........SEE WWUS76 KMTR - SFONPWMTR FOR DETAILS *

WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER
CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

RAIN COULD BE HEAVY WEDNESDAY MORNING BUT WILL TAPER OFF IN THE
AFTERNOON. RAIN CHANCES WILL DIMINISH FURTHER WEDNESDAY NIGHT AND
THURSDAY. RAIN IS FORECAST TO SPREAD OVER THE REGION ONCE AGAIN
THURSDAY NIGHT AND FRIDAY BUT IS NOT EXPECTED TO BE PARTICULARLY
HEAVY. ANOTHER STORM WILL SPREAD RAIN FROM NORTH TO SOUTH ACROSS THE
REGION SATURDAY NIGHT THROUGH SUNDAY NIGHT.

.SPOTTER INFORMATION STATEMENT...

WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER
CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES.

CAZ515>518-121300-
BIG SUR COAST-
SOUTHERN SALINAS VALLEY/ARROYO SECO AND LAKE SAN ANTONIO-
SANTA LUCIA MOUNTAINS AND LOS PADRES NATIONAL FOREST-
MOUNTAINS OF SAN BENITO COUNTY AND INTERIOR MONTEREY COUNTY
INCLUDING PINNACLES NATIONAL MONUMENT-
145 PM PDT TUE APR 11 2006

THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE MONTEREY BAY AREA.

.DAY ONE...TUESDAY AND TUESDAY NIGHT

A STRONG STORM IS FORECAST TO MOVE SOUTH OFF THE CALIFORNIA COAST
TUESDAY AND TUESDAY NIGHT. LIGHT TO MODERATE RAIN IS FORECAST TO
SPREAD ACROSS THE REGION TUESDAY AND CONTINUE TUESDAY NIGHT INTO
WEDNESDAY MORNING. THE GREATEST RAINFALL AMOUNTS ARE PROJECTED TO
BE NORTH OF MONTEREY BAY...FROM THE SANTA CRUZ MOUNTAINS NORTHWARD.
LOCALLY HEAVY RAIN IS POSSIBLE NEAR MONTEREY BAY LATE TUESDAY AND
TUESDAY NIGHT WHICH MAY RESULT IN LOCAL URBAN FLOODING.

WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER
CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

RAIN WILL TAPER OFF WEDNESDAY AFTERNOON. RAIN CHANCES WILL DIMINISH
FURTHER WEDNESDAY NIGHT AND THURSDAY. RAIN IS FORECAST TO SPREAD OVER
THE REGION ONCE AGAIN THURSDAY NIGHT AND FRIDAY AND RAIN COULD BE
HEAVY AT TIMES THURSDAY NIGHT AND FRIDAY MORNING...MAINLY FROM
MONTEREY BAY SOUTHWARD. ANOTHER STORM WILL SPREAD RAIN FROM NORTH TO
SOUTH ACROSS THE REGION LATE SUNDAY THROUGH SUNDAY NIGHT.

DYKEMA