Stormy Weather Ahead

HYDROLOGIC OUTLOOK
latest NATIONAL WEATHER SERVICE SAN DIEGO CA
1220 PM PST FRI JAN 15 2010


THE INLAND EMPIRE- RIVERSIDE COUNTY MOUNTAINS-
1220 PM PST FRI JAN 15 2010


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

A STORMY PATTERN IS SETTING UP ACROSS THE EASTERN PACIFIC OCEAN THAT
WILL BRING PERIODS OF MODERATE TO HEAVY RAIN AND MOUNTAIN SNOW TO
SOUTHERN CALIFORNIA MOST OF NEXT WEEK AND POSSIBLY INTO THE
FOLLOWING WEEK.

A STRONG PACIFIC JET STREAM HAS DEVELOPED OVER THE PACIFIC OCEAN
THAT WILL DRIVE A SERIES OF MOISTURE LADEN STORMS ACROSS SOUTHERN
CALIFORNIA. ONCE THE HEAVIER PRECIPITATION BEGINS MONDAY...IT WILL
LIKELY CONTINUE ON THE COASTAL SLOPES UNABATED FOR MUCH OF THE WEEK
DUE TO UPSLOPE FLOW. AT LOWER ELEVATIONS...BREAKS IN THE RAINFALL
ARE MORE LIKELY WITH THE HEAVIER RAIN ACCOMPANYING FRONTS. TIMING OF
THESE FEATURES WILL BE DIFFICULT DUE TO THE SPEED OF THE JET STREAM
ALOFT.

SNOW LEVELS WILL MOSTLY FLUCTUATE BETWEEN 5500 AND 6500 FEET WHICH
WOULD CONFINE HEAVY SNOW ACCUMULATIONS TO THE HIGHER ELEVATIONS IN
THE SAN BERNARDINO AND SAN JACINTO MOUNTAINS. SNOW LEVELS COULD BE
LOCALLY LOWER OR HIGHER AT TIMES NEXT WEEK WITH SOME OF THE STORMS.

BASED ON HISTORIC PATTERNS...THIS WEEK-LONG EVENT HAS THE POTENTIAL
TO GENERATE RAINFALL OF 5 TO 8 INCHES NEAR THE COAST...TO 20 OR
MORE INCHES ON THE COASTAL MOUNTAIN SLOPES. TYPICALLY WETTER
LOCATIONS ON THE COASTAL MOUNTAINS SLOPES COULD RECEIVE 30 OR MORE
INCHES OF RAINFALL. AT HIGHER ELEVATIONS IN THE SAN BERNARDINO
MOUNTAINS... MOSTLY ABOVE 6000 FEET...4 OR MORE FEET OF SNOWFALL IS
POSSIBLE.

SHOULD EXCESSIVE RAINFALL DEVELOP AS FORECAST...UNREGULATED REACHES
OF MAINSTREAM RIVERS INCLUDING THE SANTA MARGARITA...SAN LUIS
REY...AND SAN DIEGO...ARE LIKELY TO HAVE SIGNIFICANT FLOW BY THE END
OF THE WEEK. DEPENDING ON THE CONDITION OF THE CHANNELS...HEAVY
FLOWS COULD RESULT IN FLOODING OF LOW-LYING AREAS ADJACENT TO THE
RIVERS ONCE UNDERGROUND AQUIFERS FILL. IT HAS BEEN SEVERAL YEARS
SINCE HEAVY FLOWS HAVE DEVELOPED IN THESE RIVERS...SO LOCAL
INTERESTS SHOULD PREPARE FOR POSSIBLE FLOODING...INCLUDING
IMPASSIBLE LOW-WATER CROSSINGS.

IN THE UPPER DESERTS...RAINFALL OF 5 TO 10 INCHES ON THE NORTH
SLOPES OF THE SAN BERNARDINO MOUNTAINS AND 2 TO 4 INCHES IN DESERT
AREAS SHOULD PRODUCE FLOW IN THE MOJAVE RIVER...WITH FLOODING
POSSIBLE THE LATTER HALF OF THE WEEK DEPENDING ON THE RELEASES FROM
SILVERWOOD RESERVOIR AND THE MOJAVE DAM.

IN THE LOWER DESERTS...RAINFALL OF 1.5 TO 3.5 INCHES FOR THE WEEK
ARE EXPECTED. THIS ALONE WOULD CAUSE PERIODS OF URBAN AND SMALL
STREAM FLOODING. HOWEVER THE NORMALLY DRY WHITE WATER RIVER IN THE
COACHELLA VALLEY WILL LIKELY BE FLOWING FROM THE EXCESSIVE RUNOFF
COMING FROM THE MOUNTAINS. THIS WOULD MAKE ROADS CROSSING THROUGH
THE WHITE WATER RIVER CHANNEL IMPASSABLE.

AS THE WEEK PROGRESSES...MOST STREAMS AND NORMALLY DRY WASHES WILL
BE FLOWING. AS THE SOIL BECOMES SATURATED...RECENTLY BURNED AREAS
WILL BECOME SUSCEPTIBLE TO DANGEROUS...LIFE-THREATENING DEBRIS
FLOWS.

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.