Hydrologic Outlook

HYDROLOGIC OUTLOOK
CAZ034>041-044>046-051>054-059-087-088-547-548-190200-

HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
520 AM PST MON JAN 18 2010

...EXTENDED PERIOD OF SIGNIFICANT RAIN AND MOUNTAIN SNOW NEXT WEEK
FOR SOUTHERN CALIFORNIA...

A VERY POWERFUL WEST TO EAST JET STREAM WILL ALLOW A SERIES OF
STRONG STORM SYSTEMS TO TRACK INTO SOUTHERN CALIFORNIA NEXT WEEK.

A SIGNIFICANT AND POSSIBLY EXCESSIVE RAINFALL EVENT WILL OCCUR OVER
SOUTHWESTERN CALIFORNIA DURING THE UPCOMING WEEK. RAIN COVERAGE AND
INTENSITY IS EXPECTED TO INCREASE ACROSS THE REGION TODAY AND THIS
EVENING. THIS FIRST STORM SYSTEM IS EXPECTED TO BRING 1 TO 3 INCHES
ACROSS MOST COASTAL AND VALLEY AREAS THROUGH THIS EVENING...WITH 3
TO 5 INCHES ACROSS FOOTHILL AND MOUNTAIN AREAS. LOCAL AMOUNTS UP TO
6 INCHES ARE POSSIBLE ACROSS FAVORED SOUTH FACING SLOPES. THERE WILL
BE SCATTERED THUNDERSTORMS THIS AFTERNOON AND EVENING. ESTIMATED
PEAK HOURLY RAINFALL RATES BETWEEN 0.75 INCHES AND 1.00 INCH PER
HOUR ARE POSSIBLE THIS AFTERNOON AND EVENING...EXCEPT LOCALLY UP
TO 1.25 INCHES PER HOUR ON FAVORED SOUTH FACING SLOPES AND NEAR
THUNDERSTORMS.

A SECOND AND WEAKER STORM SYSTEM IS EXPECTED TO AFFECT THE REGION
TUESDAY AFTERNOON INTO TUESDAY NIGHT. THE THIRD AND MOST LIKELY
STRONGEST STORM SYSTEM OF THE WEEK IS EXPECTED WEDNESDAY AFTERNOON
INTO THURSDAY NIGHT. A COLD AND UNSTABLE AIR MASS WILL CONTINUE TO
KEEP A THREAT OF SHOWERS ON FRIDAY. FOR THE ENTIRE WEEK...RAINFALL
TOTALS OF 4 TO 8 INCHES CAN BE EXPECTED IN COASTAL AND VALLEY
AREAS...AND 8 TO 16 INCHES IN THE FOOTHILLS AND MOUNTAINS. LOCAL
RAINFALL AMOUNTS OVER 20 INCHES WILL BE POSSIBLE ACROSS FAVORED
SOUTH FACING COASTAL SLOPES. ACROSS THE ANTELOPE VALLEY...RAINFALL
TOTALS OF 2 TO 4 INCHES CAN BE EXPECTED THROUGH FRIDAY...WITH
LOCALLY HIGHER AMOUNTS IN THE FOOTHILLS. THIS WILL LIKELY BE THE
WETTEST WEEK SINCE EARLY 2005.

SNOW LEVELS WILL GENERALLY RANGE BETWEEN 6500 AND 7000 FEET ON
TODAY...THEN LOWER TO BETWEEN 5500 AND 6000 FEET TONIGHT. SNOW
LEVELS ARE THEN EXPECTED TO RANGE BETWEEN 5000 AND 6000 FEET FOR THE
REMAINDER OF THE WEEK.

THE CUMULATIVE EFFECT OF THESE STORM SYSTEMS MAY BRING FLOODING
THREATS TO THE REGION ON A SCALE THAT HAS NOT BEEN SEEN SINCE 2005.
LARGE AMOUNTS OF EXPECTED PRECIPITATION...AS WELL AS THE POTENTIAL
FOR HIGH INTENSITY RAINFALL...WILL BRING THE THREAT OF SIGNIFICANT
FLASH FLOODING AND POTENTIALLY DEADLY DEBRIS FLOWS...ESPECIALLY TO
THE RECENT BURN AREAS. THERE WILL ALSO BE A THREAT OF URBAN AND
SMALL STREAM FLOODING AND NUMEROUS ROCKSLIDES...ESPECIALLY LATER IN
THE WEEK AS SOILS BECOME MORE SATURATED. AS THE WEEK
PROGRESSES...MOST STREAMS AND NORMALLY DRY WASHES WILL BE FLOWING.
IF THE STRONG STORM MATERIALIZES FOR THE WEDNESDAY AFTERNOON THROUGH
THURSDAY TIME FRAME...THERE COULD ALSO BE SOME MAIN STEM RIVER
FLOODING CONCERNS.

PERSONS LIVING IN AND CLOSE TO RECENTLY BURNED AREAS OR IN LOW-LYING
AREAS SUBJECT TO RIVER AND STREAM FLOODING SHOULD STAY TUNED FOR
LATER FORECASTS AND WARNINGS. LISTEN TO LOCAL NEWS MEDIA AND NOAA
WEATHER RADIO FOR UPDATES.

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