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

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HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
1242 PM PST WED MAR 2 2016

SERIES OF STORM SYSTEMS TO ARRIVE IN CALIFORNIA

BEGINNING AS EARLY AS THURSDAY, MARCH 3, THE BAY AREA`S PREVIOUS
MID-WINTER DRY SPELL WILL MAKE AN ABOUT-FACE INTO A PREDOMINANTLY
WET PATTERN. RAINFALL ON THURSDAY WILL BE LIGHT, WITH ACCUMULATION
GENERALLY WELL LESS THAN AN INCH AND MOSTLY CONCENTRATED FROM THE
SANTA CRUZ MOUNTAINS NORTHWARD. BY FRIDAY MORNING ONLY THE SANTA
CRUZ MOUNTAIN AND THE COASTAL MOUNTAINS OF SONOMA COUNTY MAY
RECEIVE RAINFALL IN EXCESS OF AN INCH. AGAIN, LIGHT RAIN IS
EXPECTED THROUGH FRIDAY, BUT RAINFALL INTENSITY IS EXPECTED TO
INCREASE IN THE OVERNIGHT HOURS.  TOTALS FOR THE 24-HOUR PERIOD
BEGINNING FRIDAY AT 4AM LOCAL EXTENDING TO SATURDAY 4AM ARE LIKELY
TO REACH 1-2 INCHES IN COASTAL MOUNTAINS THROUGHOUT THE SERVICE
AREA, INCLUDING THE SANTA LUCIAS IN MONTEREY COUNTY. A
CONTINUATION OF INTENSE RAIN WILL FOLLOW, WITH SEVERAL MORE INCHES
FALLING OVER SATURDAY AND SUNDAY, AGAIN CONCENTRATED IN COASTAL
RANGES. SIX-DAY TOTALS, EXTENDING FROM WEDNESDAY MARCH 2 THROUGH
EARLY TUESDAY MORNING, SHOULD YIELD 4-7 INCHES IN COASTAL
MOUNTAINS AND 1-3 INCHES IN VALLEY FLOORS AND INLAND AREAS.

UNCERTAINTY REMAINS ON THE SPECIFICS OF WEATHER PATTERNS FOR NEXT
WEEK. ALTHOUGH MOST MODELS AND FORECASTER INPUT SUGGEST CONTINUED
WET WEATHER THROUGH NEXT WEEK, THE EXACT TIMING, LOCATION, AND
AMOUNT REMAIN UNCERTAIN. WITH WET WEATHER EXPECTED FOR NEXT WEEK,
FOLLOWING SEVERAL INCHES OF RAIN OVER THE WEEKEND, RAIN WILL
LIKELY BE FALLING ON NEAR-SATURATED TO SATURATED SOILS. THUS
WATERSHEDS WILL BE PRIMED TO QUICKLY CONVERT RAIN INTO RUNOFF AND
WILL ALSO HAVE THE POTENTIAL TO GENERATE DEBRIS FLOWS AND
LANDSLIDES IN SATURATED AREAS WHERE RAINFALL RATES EXCEED 1-INCH
PER HOUR.

IMPACTS ASSOCIATED WITH THE RAINFALL EXTENDING THROUGH THE WEEKEND
WILL LIKELY BE LIMITED TO URBAN FLOODING IN AREAS WHERE STORM
DRAINS BECOME CLOGGED OR OVERWHELMED BY RUNOFF DURING INTENSE
BURSTS OF RAIN. LOW LYING AGRICULTURAL AREAS MAY ALSO EXPERIENCE
PONDING AND RUNOFF MAY ENTER ROADWAYS ADJACENT TO POORLY DRAINED
FIELDS. THE EXTENT TO WHICH CREEKS MAY JUMP THEIR BANKS WILL
LARGELY DEPEND ON THE INTENSITY OF RAINFALL: INTENSE BURSTS
SEPARATED BY LIGHT RAIN OR REPRIEVES MAY PROVIDE INITIALLY DRY
WATERSHEDS TO INFILTRATE RAINFALL AND CONTAIN RUNOFF WITHIN
CHANNELS. PROTRACTED INTENSE RAIN, WHICH IS POSSIBLE (AND APPEARS
LIKELY OVER THE WEEKEND), MAY CAUSE SOME FAST RESPONDING BASINS TO
FLOOD. EXAMPLES OF THIS TYPE OF BEHAVIOR ARE LIKELY TO OCCUR IN
VALLEY SETTINGS OF THE NORTH BAY, PARTICULARLY IN THE PETALUMA
BASIN, AND THE VALLEY FORD, BODEGA, AND BLOOMFIELD AREAS FED BY
STEMPLE CREEK, SALMON CREEK, AND THE ESTERO AMERICANO. THE LOWER
LAGUNA DE SANTA ROSA MAY ALSO EXPERIENCE ROUTINE FLOODING AND
DRAINAGE IMPACTS. QUICK URBAN DRAINAGE IN THE SANTA CLARA VALLEY
CREEKS THAT ORIGINATE IN THE SANTA CRUZ MOUNTAINS MAY ALSO
EXPERIENCE PROBLEMS. NOTABLY, WE WILL BE WATCHING THE LOS GATOS-
GUADALUPE BASIN CLOSELY, AS WELL AS UPPER LLAGAS, SARATOGA,
STEVENS, PERMANENTE, AND OTHER INTERVENING LOCAL DRAINAGES.
HOWEVER, MOST CREEKS AND RIVERS IN THE SERVICE AREA WILL REMAIN
BELOW FLOOD LEVELS, BASED ON THE EXPECTED RAINFALL RATES DESCRIBED
HERE. SHOULD RAINFALL FORECASTS INCREASE, THIS STORY MAY CHANGE,
SO PLEASE STAY TUNED TO UPDATES FROM THE SAN FRANCISCO BAY AREA
NWS OFFICE.

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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