Flood Potential Outlook
Issued by NWS San Francisco Bay Area, CA

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HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
404 PM PST WED JAN 20 2016

MORE RAIN EXPECTED WITH FLOODING AND DEBRIS FLOWS POSSIBLE

ALTHOUGH OUR WINTER SO FAR THIS WATER YEAR HAS NOT BEEN
PROLIFICALLY WET, IT HAS BEEN CONSISTENTLY WET, WITH MANY RAIN
GAGES AROUND THE GREATER BAY AREA REPORTING AROUND OR ABOVE
AVERAGE FOR THIS TIME OF YEAR. THE LATEST FEW STORMS, PARTICULARLY
THE MOST RECENT SYSTEM, HAVE DELIVERED MUCH OF THIS RAIN, WITH
MANY LOCATIONS OVER THE PAST WEEK RECEIVING IN EXCESS OF 5 INCHES.
AS A RESULT, THE MOST RECENT STORM SYSTEM HAS CAUSED A FEW ROCK
SLIDES, URBAN FLOODING, AND SOME SMALL CREEKS TO RISE ABOVE
BANKFULL CONDITIONS.

WITH PERHAPS A 36 TO 48 DRY DOWN PERIOD, MANY LOCAL STREAMS WILL
RECEDE AND SOILS WILL DRAIN BUT NOT DRY COMPLETELY. HOWEVER,
CONDITIONS ARE AGAIN EXPECTED TO BE STORMY THURSDAY NIGHT AND
FRIDAY NIGHT INTO SATURDAY. EXPECTATIONS ARE FOR AT LEAST SEVERAL
INCHES TOTAL RAINFALL IN COASTAL MOUNTAINS, AND PERHAPS 0.75" TO
1.0" IN URBAN AREAS. BECAUSE OF WATERSHED SATURATION, SLOW
DRAINAGE FROM PRIOR STORMS IN SOME LOCATIONS, SO-CALLED KING TIDES
DURING THE NEXT FEW DAYS, AND LARGE SWELL AND WAVES AT THE COAST,
FLOODING AND SLOPE STABILITY ISSUES ARE EXPECTED.

THE MAIN CONCERN IN THE COASTAL MOUNTAINS OF THE NORTH BAY, THE
SANTA CRUZ MOUNTAINS, AND THE SANTA LUCIAS ARE DEBRIS FLOWS AND
LANDSLIDES. SOILS ARE FULLY SATURATED AND ARE EXPECTED TO BE
UNSTABLE ON STEEP SLOPES WHERE RAINFALL RATES GENERALLY EXCEED
0.75" IN 1 HOUR. THIS CRITERIA MAY BE LOWER AS WE MOVE FURTHER
INTO THE LATTER STORM SYSTEM ON FRIDAY NIGHT AND SATURDAY, WHEN
CONDITIONS WILL BE OVERSATURATED IN MANY SPOTS. EXPECT FLASH FLOOD
WATCHES AND WARNINGS ISSUED IN ANTICIPATION OF SLOPE STABILITY
CONCERNS IN THESE AREAS.

IN THE NORTH BAY WE CONTINUE TO WATCH CREEKS IN THE LAGUNA DE
SANTA ROSA RECEDE FROM THE PRIOR STORM SYSTEM YESTERDAY. THESE
LOCATIONS, ALONG WITH OTHER LOW LYING DRAINAGES IN THE AREA, WILL
BE QUICK TO RESPOND TO ADDITIONAL RAIN AND WE EXPECT MANY OF
THESE LOCATIONS TO CAUSE AT LEAST MINOR FLOODING ISSUES. LOCATIONS
OF CONCERN INCLUDE CREEKS WITHIN THE LAGUNA DE SANTA ROSA AREA,
PETALUMA AREA STREAMS, AND THE VALLEY FORD, BODEGA, AND BLOOMFIELD
AREAS FED BY STEMPLE CREEK, SALMON CREEK, AND ESTERO AMERICANO.
SOME LOCATIONS ON THE MAINSTEM RUSSIAN RIVER MAY RISE CLOSE TO
MONITOR STAGE, BUT WE DO NOT EXPECT FLOODING TO OCCUR ON THE
MAINSTEM RUSSIAN RIVER FROM THESE STORM SYSTEMS. IF SUFFICIENT
STORM ENERGY MOVES EAST INTO NAPA COUNTY, SOME CREEKS IN THE NAPA
BASIN MAY RISE QUICKLY, POSSIBLY TO FLOOD STAGE. WE WILL SEND OUT
FLASH FLOOD WATCHES IN THESE AREAS WHEN AND WHERE APPROPRIATE AS
WE MONITOR THE COMING STORM SYSTEMS.

ALONG THE PENINSULA HEAVY RAIN RATES MAY CAUSE URBAN FLOODING,
ESPECIALLY DURING HIGH TIDE AND WHEN SWELL HEIGHT AND PERIOD
INCREASE THROUGH THE STORM SYSTEM. IN FACT, DRAINAGES INTERIOR TO
THE SF BAY MAY EXPERIENCE COASTAL FLOODING AND DELAYED RUNOFF
EVACUATION DUE TO THE HIGHER THAN NORMAL WATER LEVELS EXPECTED AT
THE COAST. RUNOFF DISCHARGING INTO COASTAL LOCATIONS WITH HIGH
WATER LEVELS WILL BE PROBLEMATIC IN THE INTERIOR SF BAY, BUT ALSO
ALONG THE OPEN COAST WHERE INFRASTRUCTURE AND PUBLIC ACCESS EXISTS
BELOW OUR COASTAL CLIFF LINES. THIS WOULD INCLUDE MOST RIVER
MOUTHS, AND THE ENTIRE COASTLINE BETWEEN THE WATSONVILLE AREA AND
THE SALINAS RIVER MOUTH. COMMUNITIES IN THE RIO DEL MAR AREA OF
APTOS AND PAJARO DUNES WILL BE PARTICULARLY SUSCEPTIBLE TO THE
EFFECTS OF RAIN COUPLED WITH HIGH TIDES AND WAVES.

SOUTH BAY URBAN AREAS WILL ALSO BE OF CONCERN, ESPECIALLY
DRAINAGES FLOWING EAST OUT OF THE SANTA CRUZ MOUNTAINS. WE WILL
ALSO BE WATCHING CORRALITOS/SALSIPUEDES CREEK AND WEST LITTLE
LLAGAS CREEK IN MORGAN HILL FOR SIGNS OF RAPID RISE AND POTENTIAL
FLOODING. WITH HEAVY LOCALIZED RAINFALL IN MONTEREY COUNTY
POSSIBLE, SOME AGRICULTURAL FIELDS AND ADJACENT ROADWAYS IN THE
GREATER SALINAS RIVER FLOODPLAIN MAY BECOME INUNDATED, SO CAUTION
IS ALSO ADVISED IN THESE AREAS AS ROADWAYS MAY BECOME FLOODED.

PLEASE STAY TUNED TO LOCAL MEDIA OUTLETS AND OUR OWN NWS SOCIAL
MEDIA ACCOUNTS AND WEB PAGE FOR ADDITIONAL AND UPDATED INFORMATION
PRECEDING AND DURING THE STORM.  AND PLEASE STAY SAFE!

$$

STRUDLEY



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