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Hydrologic Outlook

HYDROLOGIC OUTLOOK
CAZ006-505>513-516>518-528>530-270845-

HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
1243 PM PST WED NOV 26 2014

...STRONG PACIFIC STORMS WILL BRING HEAVY RAIN TO SF/MONTEREY BAY AREA...

BEGINNING LATE FRIDAY AND EXTENDING THROUGH MID-WEEK NEXT WEEK, A
SERIES OF STRONG PACIFIC STORMS ARE EXPECTED TO BRING PERIODS OF
HEAVY AND EXTENDED PRECIPITATION TO THE SAN FRANCISCO AND MONTEREY
BAY AREA. RAIN IS EXPECTED TO MOVE INTO THE BAY AREA FROM THE
NORTH BEGINNING FRIDAY AFTERNOON OR EVENING AND WORK ITS WAY SOUTH
THROUGH THE SF AND MONTEREY BAY REGION. ACCUMULATIONS ARE EXPECTED
TO BE GREATEST IN THE NORTH BAY (PRIMARILY SONOMA COUNTY), THE
SANTA CRUZ MOUNTAINS, AND ISOLATED NORTHERN PORTIONS OF THE SANTA
LUCIA RANGE IN MONTEREY COUNTY. RAIN TOTALS THROUGH WEDNESDAY DECEMBER
3 ARE EXPECTED TO REACH 5 TO 7 INCHES IN THESE AREAS, WITH LOWER
LYING AREAS RECEIVING LESS, GENERALLY IN THE 3-5 INCH RANGE IN THE
SF BAY AREA AND 2-4 INCHES IN THE MONTEREY BAY REGION. WE EXPECT
THE PRECIPITATION TO OCCUR IN TWO MAIN PULSES: THE FIRST STORM
IS SLATED FOR FRIDAY THROUGH THE WEEKEND, WHILE THE SECOND STORM
SYSTEM SHOULD BEGIN EARLY IN THE NEXT WORK WEEK (MONDAY OR
TUESDAY) AND EXTEND THROUGH WEDNESDAY OR THURSDAY. IT IS UNCLEAR
AT THIS POINT IN TIME IF WET WEATHER WILL CONTINUE TO PERSIST
THROUGH THE REST OF THE WORK WEEK.

IMPACTS:
SEASONAL RAINFALL ACCUMULATIONS AND LOCAL STREAMFLOW RECORDS
SUGGEST BAY AREA WATERSHEDS ARE NOT QUITE PRIMED FOR A QUICK
RESPONSE TO THE FIRST STORM SYSTEM, THUS REDUCING, OR POTENTIALLY
ELIMINATING, THE THREAT OF SMALL STREAM FLOODING FOR THE FIRST
WAVE OF RAINFALL. HOWEVER, INTENSE BURSTS OF RAINFALL ARE
POSSIBLE, AND IF THEY OCCUR, LOCAL PROBLEM SPOTS IN URBAN AND LOW-
LYING AGRICULTURAL AREAS MAY EXPERIENCE MINOR PONDING.
ADDITIONALLY, HEAVY BURSTS OVER THE BIG SUR AREA MAY BE SUFFICIENT
TO CAUSE CONCERN OVER DEBRIS FLOWS IN THE SYCAMORE CANYON AREA DUE
TO THE PRESENCE OF THE PFEIFFER FIRE BURN SCAR.

THE BREAK BETWEEN STORM SYSTEMS WILL GIVE A HELPFUL REPRIEVE IN RAINFALL.
REGARDLESS, THE THREAT OF SMALL STREAM AND URBAN FLOODING WILL BE
SLIGHTLY ELEVATED EARLY IN THE NEXT WORK WEEK COMPARED TO THE
FRIDAY-SATURDAY STORM SYSTEM, SIMPLY BECAUSE THE WATERSHEDS AND
STORM DRAINS MAY STILL BE SHEDDING RUNOFF FROM THE FIRST RAINFALL
EVENT. FLOODING AND PONDING CONCERNS IN URBAN AREAS WILL BE MORE
LIKELY WITH THIS SECOND WAVE OF PRECIPITATION. WE EXPECT TO SEE THESE
EFFECTS WITHIN THE GREATER URBAN CORRIDOR OF THE SOUTH BAY AND
PENINSULA, AND POTENTIALLY EXTENDING INTO THE EAST BAY URBAN AREAS
RINGING THE BAY. IN THE NORTH BAY, URBAN AND LOW LYING AREAS MAY
ALSO EXPERIENCE DRAINAGE ISSUES (FOR EXAMPLE, THE LOWER LAGUNA DE
SANTA ROSA AND SURROUNDING AREAS, LOWER SONOMA VALLEY NEAR
SCHELLVILLE, VALLEY FORD AND BLOOMFIELD ALONG THE ESTERO
AMERICANO, FALLON AND TWO ROCK IN THE VICINITY OF STEMPLE CREEK,
AND PETALUMA). RAINFALL DURATION AND INTENSITY MAY BE HIGH ENOUGH
TO CAUSE SOME SMALL CREEKS TO REACH OR SLIGHTLY EXCEED FLOOD
STAGE. SHOULD HEAVY RAIN OCCUR DURING HIGH TIDE, BAY-SIDE LOCALES
MAY BE MORE LIKELY TO EXPERIENCE DRAINAGE PROBLEMS. IN MORE
MOUNTAINOUS TERRAIN IN THE GREATER BAY AREA, THE MAIN THREAT WILL
LIKELY BE DOWNED TREES AND THE POTENTIAL FOR DEBRIS FLOWS ON
SATURATED STEEP HILLSIDES.

FOR BOTH STORM SYSTEMS, LARGER RIVERS IN THE AREA ARE NOT EXPECTED
TO FLOOD.

BE SAFE, AND EXERCISE CAUTION, PARTICULARLY IN URBAN AREAS WHERE
PONDING AND DRAINAGE PROBLEMS DEVELOP. STAY TUNED TO LOCAL MEDIA
OUTLETS, WEATHER RADIO, NATIONAL WEATHER SERVICE WEB RESOURCES,
AND SOCIAL MEDIA. HEED INSTRUCTIONS AND WARNINGS DELIVERED BY
LOCAL EMERGENCY MANAGEMENT OFFICIALS.

WWW.WEATHER.GOV/SANFRANCISCO

WWW.FACEBOOK.COM/NWSBAYAREA

TWITTER.COM/NWSBAYAREA
@NWSBAYAREA

WWW.YOUTUBE.COM/NWSBAYAREA

$$

STRUDLEY






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