Flood Potential Outlook
Issued by NWS Los Angeles, CA

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Hydrologic Outlook
National Weather Service Los Angeles/Oxnard CA
547 AM PST Tue Jan 17 2017

...SERIES OF STORMS WILL AFFECT SOUTHWEST CALIFORNIA WEDNESDAY
NIGHT THROUGH MONDAY RESULTING IN MULTIPLE FLOODING CONCERNS...

CONFIDENCE IS BUILDING FOR A PERIOD OF SIGNIFICANT RAINFALL AND
MOUNTAIN SNOW FOR SOUTHWEST CALIFORNIA WEDNESDAY NIGHT THROUGH
MONDAY...BRINGING THE POTENTIAL FOR NUMEROUS HYDROLOGICAL IMPACTS.

THE FIRST STORM IS EXPECTED TO BRING MODERATE RAINFALL TO
SOUTHWEST CALIFORNIA...WITH A SLIGHT CHANCE OF THUNDERSTORMS
BRINGING LOCALLY HEAVY DOWNPOURS. THIS SYSTEM WILL LIKELY BRING
BETWEEN 0.50 AND 1.00 INCH WITH LOCALLY HIGHER AMOUNTS ACROSS THE
COASTAL FOOTHILLS AND MOUNTAINS.

A SECOND STORM IS EXPECTED TO BRING A PERIOD OF MODERATE TO HEAVY
RAINFALL AND MOUNTAIN SNOW LATE THURSDAY NIGHT THROUGH EARLY
SATURDAY...WITH THE HEAVIEST RAINFALL EXPECTED ON FRIDAY.
PRELIMINARY RAINFALL ESTIMATES ARE FOR 1 TO 2 INCHES OF RAIN FROM
THIS STORM...WITH LOCAL TOTALS UP TO 3 INCHES ACROSS COASTAL
FOOTHILLS AND MOUNTAINS.

THE THIRD AND STRONGEST STORM WILL LIKELY AFFECT THE REGION
SUNDAY INTO MONDAY BRINGING THE POTENTIAL FOR HEAVY RAIN AND
MOUNTAIN SNOW. THERE IS SOME UNCERTAINTY WITH THE EXACT TIMING OF
THE HEAVIEST RAIN...BUT IT IS MOST LIKELY TO OCCUR SUNDAY NIGHT
OR MONDAY. WHILE IT IS STILL VERY EARLY...THERE IS THE POTENTIAL
FOR THIS STORM TO BRING WIDESPREAD RAINFALL AMOUNTS BETWEEN 1.50
AND 3.00 INCHES...WITH LOCAL AMOUNTS UP TO 5.00 INCHES ACROSS THE
COASTAL FOOTHILLS AND MOUNTAINS.

THE COMBINATION OF THESE THREE STORMS COULD BRING SIGNIFICANT
RAINFALL TO SOUTHWEST CALIFORNIA FROM LATE WEDNESDAY THROUGH
MONDAY...WITH MANY AREAS LIKELY TO RECEIVE BETWEEN 3 AND 6 INCHES
OF RAIN. FAVORED COASTAL FOOTHILL AND MOUNTAIN AREAS COULD HAVE
TOTALS AS HIGH AS 6 TO 9 INCHES. SEVERAL FEET OF NEW SNOW ARE
POSSIBLE FOR THE HIGHER MOUNTAIN COMMUNITIES AND SKI RESORTS
BY NEXT MONDAY.

THE EXPECTED HIGH RAINFALL AMOUNTS AND INTENSITIES COULD BRING
NUMEROUS HYDROLOGICAL IMPACTS. MANY RIVERS AND STREAMS COULD SEE
SIGNIFICANT FLOWS LATER THIS WEEK INTO EARLY NEXT WEEK. THERE IS A
POTENTIAL FOR SWIFT WATER RESCUE ISSUES DUE TO THE HEAVY RAIN AND
RESULTING INCREASED FLOW RATES. THERE WILL BE THE THREAT OF FLASH
FLOODING WITH MUD AND DEBRIS FLOWS IN AND AROUND THE RECENT BURN
AREAS...ESPECIALLY WITH THE FRIDAY AND LATE SUNDAY INTO MONDAY
STORMS. ALSO...WIDESPREAD AND SIGNIFICANT URBAN AND SMALL STREAM
FLOODING CAN BE EXPECTED AT TIMES FRIDAY THROUGH MONDAY.
LASTLY...ROCK AND MUDSLIDES WILL BE A SIGNIFICANT THREAT DURING
THIS PERIOD...ESPECIALLY NEAR CANYON ROADWAYS.

WATCH FOR UPDATES AND POSSIBLE WATCHES AND WARNINGS AT
WEATHER.GOV/LOSANGELES AS WE GET CLOSER TO THE EVENT.

$$

GOMBERG/BRUNO/KAPLAN



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