HYDROMETEOROLOGICAL DISCUSSION
NATIONAL WEATHER SERVICE / CALIFORNIA NEVADA RFC / SACRAMENTO CA
930 AM PST WED DEC 22 2010

...MORE HEAVY PRECIP FOR SRN CA TOWARD SRN AND ERN NEV...
...HEAVY TO EXCESSIVE PRECIP INCLUDES THE DESERTS OF SE CA...
...DRYING CONDITIONS EXPECTED IN THE THU AND FRI TIME PERIODS...

.24 HOUR PRECIPITATION TOTALS (ENDING DEC 22 AT 400 AM PST)...

A LARGE MOISTURE FETCH FROM THE SOUTHERN CA COAST INLAND ACROSS THE 
SE CA DESERTS ALONG WITH EXTREME SOUTHERN AND EASTERN NEV BROUGHT 
HEAVY PRECIP TO SIMILAR AREAS AGAIN. THE NEXT COLD FRONT BEGAN TO 
MOVE ONTO COASTAL SECTIONS FROM PT CONCEPTION NORTHWARD...AND SPREAD 
PRECIP OVER THE SHASTA DRAINAGE ALONG WITH PORTIONS OF THE NORTHERN 
SIERRA.

BETWEEN THE EASTERN SAN GABRIEL MOUNTAINS AND THE LAGUNA MOUNTAINS 
TOTALS WERE IN THE RANGE OF 2.00- TO 5.00-INCHES WITH LOCAL TOTALS 
TO 6.00-INCHES. LOWER ELEVATIONS IN THE SAME AREA SAW AMOUNTS FROM 
1.50- TO 3.00-INCHES. THE DESERT LOCATIONS UP INTO EXTREME SOUTHERN 
AND EASTERN NEVADA SAW AMOUNTS IN THE 0.50- TO 1.50-INCH RANGE. 
HOWEVER...SOME OF THE HIGHER TERRAIN OF SOUTHERN NEV LIKE THE SPRING 
MOUNTAINS SAW IN UPWARDS OF 2.25-INCHES. 

THE SHASTA DRAINAGE SAW SOUTHERLY FLOW DEVELOP AHEAD OF THE COLD 
FRONT WHICH BROUGHT AMOUNTS OF 1.00- TO 2.00-INCHES (LOCAL 
2.50-INCHES). SIMILAR TOTALS WERE RECORDED RIGHT ON CAPE MENDOCINO 
NEAR HONEYDEW. OTHER NORTH COAST LOCATIONS WERE GENERALLY IN THE 
RANGE OF 0.75- TO 1.25-INCHES (LOCAL TO 1.75-INCHES OVER THE LOWER 
RUSSIAN RIVER BASIN). FINALLY FOR THE NORTH PART OF THE STATE...THE 
FAR NORTHERN SIERRA SAW 0.50- TO 1.25-INCHES WITH 0.10- TO 0.25-INCH 
FOR THE SACRAMENTO VALLEY. 

FOR THE CENTRAL PORTION OF CA...GREATEST AMOUNTS WERE OVER THE SANTA 
CRUZ AND SANTA LUCIA MOUNTAINS. TOTALS WERE BETWEEN 0.75- AND 
1.25-INCHES. INLAND LOCATIONS OVER THE SAN JOAQUIN VALLEY WERE NEAR 
OR LESS THAN 0.25-INCH...WHILE THE SOUTHERN SIERRA SAW 0.25-INCH OR 
LESS WITH A FEW POCKETS APPROACHING 0.50-INCH.

FINALLY...AROUND PT CONCEPTION EAST TOWARD VENTURA COUNTY...THE 
HIGHER TERRAIN SAW 1.00- TO 2.00-INCHES WHILE THE LOWER ELEVATIONS 
WERE ON THE ORDER OF 0.50- TO 1.00-INCH.

OVER THE PAST 7 DAYS...FROM THE I-80 CORRIDOR SOUTHWARD THE REGION 
HAS BEEN APPROX 400- TO 600-PERCENT OF NORMAL IN TERMS OF PRECIP 
TOTALS. THERE ARE MOST LIKELY SOME POCKETS EVEN HIGHER THAN 
600-PERCENT OF NORMAL OVER THE SE CA DESERTS UP TOWARDS EXTREME 
SOUTHERN AND EASTERN NEVADA.

.METEOROLOGICAL CONDITIONS...

AN AMAZING MOISTURE FEED CONTINUES FROM THE SOUTHERN CA COAST INLAND 
ACROSS THE COASTAL MOUNTAINS BEFORE SPILLING OVER THE SE CA DESERTS 
AND EXTREME SOUTHERN AND EASTERN NEV. GPS-MET STATIONS ALONG THE 
COAST AT POINT LOMA AND LA JOLLA PEAKED OVERNIGHT WITH AN IPW IN THE 
RANGE OF 1.25- TO 1.50-INCHES. INLAND AT THE ESSEX LOCATION (ALONG 
I-40 IN THE DESERTS)...THE IPW IS SHOWING A SLIGHT RISE TO NEARLY 
1.00-INCH AS THE AXIS OF THE HIGHEST MOISTURE CONTENT AIR MOVES 
OVERHEAD. 

22/12Z KNKX RAOB MEASURED A PW OF 1.14-INCHES (APPROX 250-PERCENT OF 
NORMAL) WITH A SATURATED PROFILE. ONSHORE FLOW HAS ALSO RAMPED UP 
OVER THE PAST 12 HOURS...ESPECIALLY IN THE LOW- TO MID-LEVELS. 
850-MB WINDS ARE UP TO 45-KT...SIMILAR TO JUST A TAD BIT HIGHER IN 
THE ATMOSPHERE AT 700-MB. THIS STRONG PUSH FROM THE SW IS RESULTING 
IN IDEAL OROGRAPHIC CONDITIONS.

AS STATED...PLENTY OF MOISTURE IS MAKING ITS WAY INLAND OVER THE 
DESERT LOCATIONS AND ACROSS MUCH OF THE GREAT BASIN...EVEN TOWARD 
THE CENTRAL ROCKIES. LOOKING AT NUMEROUS RAOBS ACROSS THIS 
AREA...ITS FAIR TO SAY THAT PW VALUES ARE EASILY TWICE NORMAL VALUES 
FOR THIS TIME OF YEAR.

88-D INDICATES WIDESPREAD PRECIP AFFECTING THESE AREAS WITH SEVERAL 
MOUNTAIN STATIONS BETWEEN PT CONCEPTION AND THE US/MEXICO BORDER 
REPORTING OVER 1.00-INCH SINCE 22/12Z. WHAT IS EVEN MORE IMPRESSIVE 
IS THE 1.01-INCHES BEING RECORDED AT APPLE VALLEY...WHICH IS OVER 
THE CREST OF THE SAN BERNARDINO MOUNTAINS NEAR THE CITY OF 
VICTORVILLE ALONG I-15. EVEN BARSTOW-DAGGETT HAS RECEIVED 0.42-INCH 
IN THE PAST 3 HOUR WITH STEADY PRECIP CONTINUING TO AFFECT THE AREA. 
FARTHER INLAND...LOWER ELEVATION LOCATIONS AT DESERT ROCK AND LAS 
VEGAS HAVE SEEN 0.56- AND 0.54-INCH RESPECTIVELY SINCE 
22/12Z...WHICH INDICATES MOST LIKELY THAT INTENSE PRECIP RATES ARE 
BEING OBSERVED OVER THE SPRING MOUNTAINS AND OTHER HIGHER ELEVATIONS 
ACROSS EXTREME SOUTHERN AND EASTERN NEV. THESE CONDITIONS LOOK TO 
PERSIST FOR THE NEXT 3 TO 9 HOURS UNTIL THE MOISTURE FEED IS FINALLY 
SHUNTED TOWARD THE SOUTH AND EAST OF THE REGION AS THE S/WV TROF 
MOVES ACROSS THE AREA.

LATEST WV IMAGERY SHOWS THE CORE OF THE S/WV TROF NOW SPINNING TO 
THE WSW OF PT CONCEPTION NEAR 32N/123W. ANOTHER CONCERN AS THE 
SYSTEM APPROACHES THE COASTAL SECTIONS OF SOUTHERN CA WILL BE THE 
THREAT OF CONVECTIVE ACTIVITY...WHICH WILL ONLY ADD TO MESS WITH 
HIGHER PRECIP RATES UNDER STRONGER CELLS. CURRENTLY...LOWEST 
STABILITY IS OFFSHORE. HOWEVER...THE 22/06Z GFS IS INDICATING THAT 
BY 22/18Z THE LEADING EDGE OF THIS COOLER AIR ALOFT AND LESS STABLE 
AIRMASS WILL REACH COASTAL SECTIONS FROM PT CONCEPTION TO NORTHERN 
BAJA. LIFTED INDICES WILL BE IN THE 0- TO MINUS 1-DEG C 
RANGE...WHILE SFC-BASED CAPES REACH JUST OVER 100-J/KG. DURING THE 
AFTERNOON HOURS IS WHEN THE CONVECTIVE THREAT WILL BE AT ITS PEAK. 
LIFTED INDICES DROP CLOSE TO MINUS 2-DEG C WITH SFC-BASED CAPE 
VALUES REACHING A PEAK OF 300-J/KG. THIS AREA IS FAIRLY WIDESPREAD 
FROM A SAN LUIS OBISPO TO LAS VEGAS LINE...INCLUDING ALL POINTS 
SOUTH TO THE US/MEXICO BORDER. WILL NEED TO KEEP AN EYE ON ANY 
STRONG CELLS THAT TRACK OVER ALREADY SATURATED BASINS FOR INTENSE 
PRECIP RATES AND ADDED RUNOFF.

AS THE CORE OF THE SYSTEM EXITS THE REGION TONIGHT...THE BEST 
INSTABILITY SHIFTS ACROSS ARIZONA. AT THIS TIME IS WHEN PRECIP WILL 
SEE A NOTICEABLE DECREASE IN COVERAGE AND INTENSITY. THERE WILL 
STILL BE SOME UPSLOPE SHOWERS FROM THE EASTERN SAN GABRIEL MOUNTAINS 
SOUTH TOWARD THE LAGUNA MOUNTAINS. LOWER ELEVATIONS WILL BEGIN TO 
DRY OUT. DESERT LOCATIONS...EXCEPT IN CLOSE PROXIMITY TO THE CORE OF 
THE SYSTEM (LOWER COLORADO RIVER BASIN) WILL ALSO BEGIN TO SEE 
PRECIP COME TO AN END.

A POSITIVELY TILTED UPR RIDGE WILL BUILD ACROSS THE AREA THU INTO 
FRI BRINGING COMPLETELY DRY CONDITIONS TO THE REGION...FINALLY! NEXT 
COLD FRONT SLOWLY APPROACHES THE NORTH COAST AS AN UPR TROF DIGS 
SOUTH OUT OF THE GULF OF ALASKA LATER ON FRI. FIRST SIGNS OF PRECIP 
ALONG THE NORTH COAST APPEAR ON THE OVERNIGHT INTO CHRISTMAS DAY 
WITH THE BULK OF THE PRECIP MOVING ACROSS THE REGION DURING THE 
DAYTIME AND EVENING HOURS. 22/00Z EC IS ABOUT 6 HOURS SLOWER THAN 
THE 22/06Z GFS...BUT TRACK THE SYSTEM IN A FAIRLY SIMILAR 
TRAJECTORY. THIS IS A BIT DEEPER THAN PREVIOUS THINKING WITH PRECIP 
MAKING ITS WAY SOUTH TO NEAR PT CONCEPTION AND EVENTUALLY THE REST 
OF SOUTHERN CA. ANOTHER SYSTEM THEN LOOKS TO MOVE INTO THE AREA FOR 
THE MIDDLE OF NEXT WEEK.


DAY 1 QPF (WED 22/12Z TO THU 23/12Z): HEAVIEST PRECIP WILL FALL IN A 
SWATH FROM THE SOUTHERN CA COAST NNE ACROSS THE SE CA DESERTS BEFORE 
SPREADING OVER EXTREME SOUTHERN AND EASTERN NEV. GREATEST TOTALS 
WILL FALL OVER THE EASTERN SAN GABRIEL AND WESTERN SAN BERNARDINO 
MOUNTAINS...AS WELL AS THE SAN JACINTO AND LAGUNA MOUNTAINS WITH 
2.00- TO 4.00-INCHES (LOCAL 5.00-INCHES). THE SANTA YNEZ AND SAN 
RAFAEL MOUNTAINS WILL SEE SLIGHTLY LESS TOTALS WITH 1.00- TO 
2.50-INCHES. FOR LOWER ELEVATION COASTAL STATIONS...EXPECT AMOUNTS 
FROM 1.00- TO 2.00-INCHES. INLAND OVER THE SE CA DESERTS TOTALS WILL 
GENERALLY RANGE FROM 0.75- TO 1.50-INCHES WITH SOME LOCAL AMOUNTS 
EXCEEDING 2.00-INCHES. FOR EXTREME SOUTHERN AND EASTERN NEVADA THE 
GREATEST AMOUNTS WILL FALL OVER THE SPRING MOUNTAINS AND THE GRANT 
RANGE WITH 1.50- TO 3.00-INCHES (LOCAL 4.00-INCHES FOR THE SPRING 
MOUNTAINS). ELSEWHERE...HIGHER TERRAIN LOCATIONS FOR THIS AREA WILL 
BE IN THE RANGE OF 1.00- TO 2.00-INCHES WITH 0.50- TO 1.00-INCH 
LOWER ELEVATIONS. FOR THE LENGTH OF THE SIERRA TOTALS WILL RANGE 
FROM 0.75-INCH NORTH TO 1.50-INCHES SOUTH. THE SHASTA DRAINAGE WILL 
SEE ANOTHER 0.25- TO 0.50-INCH. ELSEWHERE...EXPECT AMOUNTS NEAR OR 
LESS THAN 0.25-INCH.

DAY 2 QPF (THU 23/12Z TO FRI 24/12Z): DRY.

DAY 3 QPF (FRI 24/12Z TO SAT 25/12Z): A FEW LIGHT SHOWERS ALONG THE 
FAR NORTH COAST WILL RESULT IN AMOUNTS CLOSE TO 0.10-INCH.


.HYDROLOGICAL CONDITIONS...

SOUTHERN CALIFORNIA RIVERS AND STREAMS ARE EXPERIENCING MAJOR 
RENEWED RISES THIS MORNING.  FORECAST POINTS ON THE SAN DIEGO, SANTA 
MARGARITA AND MOJAVE RIVERS ARE ABOVE FLOOD STAGES.  THE WAVES OF 
HEAVY RAIN SHOULD FINALLY DECREASE LATER TODAY ALLOWING FOR MOSTLY 
RECEDING RIVERS ON THURSDAY.

IN NORTHERN AND CENTRAL CALIFORNIA MOST RIVERS AND STREAMS REMAIN 
WELL ABOVE SEASONAL NORMALS BUT AT MANAGEABLE FLOW VOLUMES.


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