Hydrologic Outlook

HYDROLOGIC OUTLOOK
CAZ043-048-050-055>058-060>062-065-552-554-180730-

HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE SAN DIEGO CA
1125 AM PST Mon Jan 16 2017

...SERIES OF PACIFIC STORMS TO IMPACT CALIFORNIA THURSDAY THROUGH
NEXT TUESDAY...

CONFIDENCE IS BUILDING FOR A SIGNIFICANT WET PERIOD ACROSS FAR
SOUTHWEST CALIFORNIA BEGINNING THURSDAY JANUARY 19TH...AND
CONTINUING THROUGH TUESDAY JANUARY 24TH. UNLIKE THE LAST Series
OF STORMS...THE STORM TRACK LATER THIS WEEK WILL BE SUPPRESSED
FAR ENOUGH SOUTH ACROSS THE PACIFIC TO INCLUDE FAR SOUTHWESTERN
CALIFORNIA IN PERIODS OF MODERATE TO BRIEFLY HEAVY PRECIPITATION.
LITTLE RECOVERY TIME IS EXPECTED BETWEEN SYSTEMS.

THIS WILL BE THE FIRST TIME SINCE 2010 THE DEVELOPING WEATHER
PATTERN WILL HAVE THE POTENTIAL TO CREATE AN EXTENDED PERIOD OF
ENHANCED RUNOFF INTO AREA STREAMS AND MAIN-STEM RIVERS. IN
ADDITION...AFTER THE FIRST AND SECOND STORMS...THE SOILS WILL
LIKELY HAVE LITTLE CAPACITY TO ABSORB MUCH MORE RAIN...WITH MOST
OF IT BECOMING RUNOFF.

THERE WILL BE THE POSSIBILITY OF FLASH FLOODING...ESPECIALLY WITH
THE STRONGER SYSTEMS THIS WEEKENDAND EARLY NEXT WEEK...DUE TO THE
POTENTIAL FOR HEAVIER RAINFALL RATES. THE GREATEST THREAT WILL
EXIST IN AND BELOW RECENT BURN SCARS AND IN POORLY DRAINED URBAN
AREAS.

Some very preliminary 6-DAY forecast rainfall totals for Thursday
through Tuesday of next week...

Coast...........2 to 4 inches.
Valleys.........3 to 5 inches.
Mountains.......5 to 10 inches.
Upper deserts...1 to 3 inches.
Lower deserts...1 to 2 inchES.

SOME FAVORED COASTAL SLOPES COULD RECEIVE A FOOT OR MORE OF RAIN.
SNOW LEVELS WILL FLUCTUATE MOSTLY BETWEEN 4500 AND 5500 FEET...
WHICH WILL HELP TO MITIGATE RUNOFF FROM THE UPPER MOUNTAIN SLOPES
INITIALLY. HOWEVER...THERE ARE INDICATIONS THE FREEZING LEVELS MAY
RISE FOR A TIME DURING THE FINAL STORM IN THIS SERIES. THIS COULD
AUGMENT RUNOFF. SEVERAL FEET OF SNOWFALL IS POSSIBLE IN THE HIGHER
MOUNTAIN COMMUNITIES BY NEXT TUESDAY.

SEVERAL OF OUR RIVER SYSTEMS HAVE NOT RECORDED SIGNIFICANT FLOW
SINCE 2010 INCLUDING THE SAN LUIS REY...SANTA MARGARITA...AND THE
MOJAVE. THE SAN DIEGO RIVER RESPONDS MORE QUICKLY TO RAINFALL AND
RUNOFF AND WILL LIKELY EXCEED MONITOR LEVEL...FLOWING OVER SOME OF
THE LOWER WATER CROSSINGS IN MISSION VALLEY AT TIMES.

PRESENT INDICATIONS ARE THAT SOMETIME THIS WEEKEND OR EARLY NEXT
WEEK...THE SANTA MARGARITA...SAN DIEGO...WHITEWATER...MOJAVE...AND
TIJUANA RIVERS MAY RECORD SIGNIFICANT FLOWS.

* THE SAN DIEGO AND SANTA MARGARITA RIVERS MAY REACH FLOOD LEVELS.
THIS WILL IMPACT TRAVEL THROUGH MISSION VALLEY... AND ON
VANDERGRIFT AND STUART MESA ROADS ON CAMP PENDLETON. ROAD
CLOSURES ARE POSSIBLE.

* FOR THE MOJAVE RIVER...PRESENT RAINFALL EXPECTATIONS WOULD NOT
RESULT IN THE RIVER REACHING FLOOD LEVEL. HOWEVER...SIGNIFICANT
FLOWS IN THE HIGH DESERT ARE RARE AND MAY IMPACT LOW WATER
CROSSINGS AND AGRICULTURAL INTERESTS IN AND NEAR THE RIVER
CHANNEL.

* THE WHITEWATER RIVER DRAINS INTO THE COACHELLA CANAL WHICH FLOWS
THROUGH HEAVILY POPULATED AREAS IN THE COACHELLA VALLEY. LOW-
WATER CROSSINGS MAY BE INUNDATED AND BARRICADED AT TIMES IF THE
FLOW BECOMES MODERATE TO HEAVY.

* THE TIJUANA RIVER TENDS TO RESPOND QUICKLY TO HEAVY RAINFALL
RATES...ESPECIALLY WHEN THE SOIL HAS BECOME SATURATED. RESIDENTS
AND INTERESTS IN THE TIJUANA RIVER VALLEY SHOULD BE PREPARED FOR
FLOODING AT TIMES THIS COMING WEEKEND AND MAKE PREPARATIONS TO
MOVE EQUIPMENT AND ANIMALS TO HIGHER GROUND IF NECESSARY.

* FLOWS ARE POSSIBLE IN THE SAN LUIS REY RIVER EARLY NEXT WEEK.
AFTER YEARS OF VERY LITTLE FLOW...DENSE OVERGROWTH HAS DEVELOPED
IN THE CHANNEL. ANY SIGNIFICANT FLOW CAN RESULT IN FLOODING DUE
TO TEMPORARY CHANNEL BLOCKAGES THAT MAY DEVELOP. LOCAL FLOODING
IS POSSIBLE IN UPSTREAM AREAS FROM BONSALL TO PAUMA VALLEY. SOME
ROAD IMPACTS OR CLOSURES ARE POSSIBLE... INCLUDING SHEARER
CROSSING...COUSER CANYON AND LILAC ROAD.

A PRELIMINARY FORECAST FROM THE CALIFORNIA-NEVADA RIVER FORECAST
CENTER HAS THE SAN DIEGO RIVER REACHING 7.5 FT BY 6 PM PST FRIDAY.
THIS MAY CAUSE SOME CLOSURES OF LOW-WATER CROSSINGS IN MISSION
VALLEY THEN. WATCH FOR LAXRVSSGX ISSUANCES FOR RIVER FORECAST
LEVELS IN THE COMING DAYS...OR CHECK THE WEB AT:
WATER.WEATHER.GOV/AHPS2/INDEX.PHP?WFO=SGX

SOME FLOODING IS LIKELY LATER THIS WEEK. EXPECT ROAD CLOSURES OR
DELAYS AT LOW-WATER CROSSINGS AND URBAN FLOODING AT TIMES OF
HEAVY RAINFALL RATES. WATCH FOR UPDATES AND POSSIBLE WATCHES AND
WARNINGS AT WEATHER.GOV/SANDIEGO AS WE GET CLOSER TO THE EVENT.


$$

JAD