HYDROMETEOROLOGICAL DISCUSSION
NATIONAL WEATHER SERVICE / CALIFORNIA NEVADA RFC / SACRAMENTO CA
930 AM PST MON DEC 20 2010

...PRECIP TO REMAIN WIDESPREAD ACROSS THE REGION THRU WED...
...FOCUS OF MOISTURE PLUME WILL BE FROM SOCAL TO SE NEVADA...

.24 HOUR PRECIPITATION TOTALS (ENDING DEC 20 AT 400 AM PST)...

WIDESPREAD PRECIP WAS RECORDED ACROSS THE AREA AS A STRONG COLD 
FRONT TRAVERSED THE REGION. GREATEST AMOUNTS WERE IN THE VICINITY OF 
A DEEP MOISTURE SOURCE THAT TRACKED BACK ACROSS THE PACIFIC TO NEAR 
HAWAII. FOR THE SOUTHERN SIERRA TOTALS WERE IN THE RANGE OF 3.00- TO 
6.00-INCHES WITH HIGHER TOTALS CLOSER TO 10.00-INCHES AT THE WETTEST 
LOCATIONS. THE NORTHERN SIERRA WAS LESS THAN THEIR COUNTERPARTS TO 
THE SOUTH WITH A RANGE OF 2.00- TO 4.00-INCHES.

SOUTHERLY FLOW AFFECTING THE TRANSVERSE RANGES FROM SANTA BARBARA TO 
SAN BERNARDINO COUNTIES ALLOWED FOR IMPRESSIVE PRECIP TOTALS AS WELL 
WITH 2.00- TO 5.00-INCHES (LOCAL 6.00- TO 8.00-INCHES) RECORDED. THE 
MAXIMUM BULLSEYES WERE IN THE EASTERN SAN GABRIEL AND WESTERN SAN 
BERNARDINO MOUNTAINS.

ACROSS THE REST OF THE HIGHER TERRAIN OF CA TOTALS GENERALLY RANGED 
FROM 1.00- TO 3.00-INCHES WITH A HEAVIER TOTAL RECORDED OVER THE 
HIGHER TERRAIN OF SAN LUIS OBISPO COUNTY WHERE PERSISTENT HEAVY 
PRECIP BROUGHT TOTALS CLOSER TO THE 4.00- TO 5.00-INCH MARK. 

THE CENTRAL VALLEY OF CA ONCE AGAIN SAW MODERATE TO HEAVY PRECIP 
MOVE ACROSS. LIGHTEST AMOUNTS WERE UP NEAR REDDING AND RED BLUFF 
WITH 0.25-INCH. SOUTH TOWARD SACRAMENTO AMOUNTS WERE CLOSER TO 
1.00-INCH. DROPPING EVEN FARTHER SOUTH INTO THE SAN JOAQUIN 
VALLEY...FRESNO WAST JUST OVER 0.50-INCH. HOWEVER...EVEN HIGHER 
AMOUNTS WERE RECORDED AT THE SOUTH END OF THE SAN JOAQUIN VALLEY 
WITH JUST OVER 1.25-INCHES AT BAKERSFIELD.

FOR THE STATE OF NEVADA...WIDESPREAD PRECIP AFFECTED THE STATE WITH 
THE HIGHER TERRAIN GENERALLY FROM 0.25- TO 0.75-INCH. THERE WERE A 
FEW LOCATIONS THAT JUMPED WELL ABOVE THESE NUMBERS IN THE SOUTHERN 
HALF OF THE STATE WITH 2.00-INCHES OR EVEN A BIT MORE. ALSO...CLOSE 
TO THE CA BORDER OVER THE EASTERN SIERRA FOOTHILLS TOTALS WERE ON 
THE ORDER OF 1.00- TO 2.00-INCHES.

.METEOROLOGICAL CONDITIONS...

POLAR UPR LOW CONTINUES TO SPIN OFF THE PACNW COAST THIS 
MORNING...SITUATED NEAR 44N/130W. S/WV TROF ROTATING THROUGH THE 
BASE OF THIS CIRCULATION IS CURRENTLY CROSSING 130W AT 33N. MOISTURE 
PLUME CONTINUES TO BE FOCUSED AT SOUTHERN CA BEFORE ADVECTING INLAND 
NE TOWARD SOUTHERN NEV. 20/12Z KVBG RAOB INDICATES 0.95-INCH OF 
AVAILABLE MOISTURE WITH A FAIRLY SATURATED COLUMN. THIS IS DOWN FROM 
A PEAK NEAR 1.25-INCHES YESTERDAY. WINDS IN THE PROFILE ARE MUCH 
WEAKER IN THE LOW-LEVELS AS COMPARED TO 12 HOURS AGO AS WELL...BUT 
STILL ONSHORE FROM THE SW. THIS IS RESULTING IN PRECIP INTENSITIES 
MUCH LOWER THAN WHAT WAS BEING EXPERIENCED ON SUNDAY. FARTHER SOUTH 
AT KNKX...THE 20/12Z RAOB IS SHOWING A PW OF 1.05-INCHES AND A 
SATURATED LAYER BETWEEN THE SFC AND 750-MB. WINDS ARE INCREASING 
UNIFORMLY FROM THE SW...AS COMPARED TO YESTERDAY/S WEAKER WESTERLY 
FLOW. AS A RESULT...PRECIP IS BEGINNING TO PICK UP ACROSS THIS PART 
OF THE STATE. 

FARTHER NORTH...CYCLONIC ONSHORE FLOW WITH NUMEROUS MID-LEVEL VORT 
MAXES MOVING ACROSS THE REGION IS CONTINUING PRECIP. AVAILABLE 
MOISTURE IS MUCH LESS TODAY...GENERALLY NEAR OR SLIGHTLY BELOW 
NORMAL FOR THIS TIME OF YEAR. PW VALUES OVER NORTHERN NEV ARE ON THE 
ORDER OF 0.25-INCH OR LESS...WHILE NORTHERN CA IS CLOSER TO 
0.50-INCH. 88-D DATA SHOWS TWO CONCENTRATED AREAS OF ECHOES. THE 
FIRST IS MOVING FROM SW-TO-NE ALONG THE COAST FROM CAPE MENDOCINO 
NORTHWARD TOWARD THE UPPER KLAMATH RIVER BASIN. THE SECOND IS A 
NARROW BAND OF PRECIP SHIFTING IN THE SAME DIRECTION FROM THE SF 
NORTH BAY COUNTIES OVER THE SOUTHERN SACRAMENTO VALLEY BEFORE 
REACHING THE NORTHERN SIERRA. GIVEN THE CONVECTIVE NATURE OF THIS 
PRECIP IN THE COLDER AIRMASS...PRECIP AMOUNTS WILL VARY THROUGH THE 
DAY WITH EVEN A FEW T-STORMS POSSIBLE. NLDN IS SHOWING A FEW 
LIGHTNING STRIKES ACROSS COASTAL SECTIONS BETWEEN THE GOLDEN GATE 
AND THE CA/ORE BORDER OVER THE PAST SEVERAL HOURS. 

INTO THE AFTERNOON AND EVENING HOURS...AS AN UPR JET ON THE BACKSIDE 
OF THE OFFSHORE POLAR UPR LOW DIVES TOWARD THE SOUTH...EXPECT 
ANOTHER SURGE OF HIGHER MOISTURE CONTENT AIR TO BE AIMED AT THE 
SOUTHERN CA COAST BETWEEN THE LA BASIN AND THE US/MEXICO BORDER. PW 
VALUES WILL JUMP APPROX 0.25- TO 0.50-INCH...WHILE ONSHORE FLOW IN 
THE LOW- AND MID-LEVELS RAMP UP. THIS WILL PROVIDE FOR IDEAL UPSLOPE 
CONDITIONS FROM THE SAN GABRIEL MOUNTAINS EAST TO THE SAN BERNARDINO 
MOUNTAINS AND THE SOUTH ACROSS THE SANTA ANA...SAN JACINTO...AND 
LAGUNA MOUNTAINS. THIS SOLUTION HAS BEEN LOCKED ON BY THE GFS FOR 
SEVERAL DAYS NOW...AND THIS LOOKS LIKE A GOOD BET TO OCCUR. THE 
20/00Z GFS-BASED OROGRAPHIC AID CONTINUES TO HIT THIS AREA FAIRLY 
HARD WITH THE 18-HOUR PERIOD ENDING TOMORROW MORNING AT 21/12Z 
SHOWING TOTALS BETWEEN 2.00- AND 6.00-INCHES (LOCALLY HIGHER FOR THE 
SAN GABRIEL MOUNTAINS). THESE NUMBERS WERE TWEAKED SLIGHTLY...BUT 
LOOK REALISTIC. THIS MOISTURE WILL ADVECT TOWARD THE NORTHEAST AND 
MOVE ACROSS THE SE CA DESERTS FOR AN IMPRESSIVE SHOT OF PRECIP FOR 
THIS AREA AS WELL. EVENTUALLY THIS MOISTURE REACHES INTO SOUTHERN 
AND EXTREME EASTERN NEV WITH WIDESPREAD PRECIP DEVELOPING.

UP TO THE NORTH...THE S/WV TROF NEAR 33N/130W WILL MOVE ACROSS THE 
I-80 CORRIDOR AND CONTINUE PRECIP THROUGH THE AFTERNOON HOURS. AS 
THIS SYSTEM MOVES INLAND THIS EVENING...PRECIP WILL ACTUALLY BE ON 
THE DECREASE. THIS PART OF THE REGION WILL BE WAITING FOR THE MAIN 
UPR TROF DIGGING OFFSHORE NEAR 130W TO BEGIN ITS TREK TOWARD THE 
WEST COAST...WHICH SHOULD BE THE LATTER HALF OF TUESDAY.

THERE ARE SLIGHT TIMING DIFFERENCES IN THE ARRIVAL OF THE OFFSHORE 
UPR TROF TOWARD THE COAST...BUT OVERALL PRECIP AMOUNTS WITH THE 
SYSTEM ARE LOOKING GOOD. FOR NOW...FOLLOWED TIMING BEING INDICATED 
BY A BLEND OF THE OPERATIONAL 20/06Z GFS AND THE 20/09Z SREF. PRECIP 
WILL BEGIN TO INCREASE ALONG COASTAL SECTIONS FROM PT CONCEPTION 
NORTHWARD DURING THE EVENING HOURS. LOW-LEVEL SOUTHERLY FLOW LOOKS 
TO REDEVELOP ACROSS SANTA BARBARA AND VENTURA COUNTIES DURING THIS 
TIME FRAME AS 850-MB WINDS JUMP UP TO THE 25- TO 35-KT RANGE. 
ALSO...THE GFS SHOWS A SECONDARY MOISTURE PLUME BEHIND THE MAIN 
MOISTURE SOURCE FARTHER TO THE SOUTH. PW VALUES WITHIN THIS 
SECONDARY PLUME ARE ON THE ORDER OF 0.75- TO 1.00-INCH. AS A 
RESULT...BROUGHT AN UPTICK TO THE PRECIP FOR THE SANTA YNEZ AND SAN 
RAFAEL MOUNTAIN RANGES.

AS THE UPR TROF AXIS REACHES THE COAST WED MORNING...PRECIP WILL 
SPREAD ACROSS MUCH OF THE REGION. WITH AN APPROACHING STRONG 
MID-LEVEL VORT MAX AT THE BASE OF THE UPR TROF...PRECIP WILL BLOSSOM 
WITH THE MAIN PW PLUME AIMED AT THE COAST OF EXTREME SOUTHERN CA AND 
SPREAD INLAND OVER THE DESERTS TOWARD EXTREME SOUTHERN NEV. 

FINALLY BY THE LATER AFTERNOON HOURS ON WED...THE UPR TROF AXIS WILL 
MOVE INLAND. THIS WILL PUSH THE BEST MOISTURE SOURCE TO THE SOUTH 
AND EAST...LEAVING DRIER CONDITIONS OVER THE REGION. LOOK FOR PRECIP 
TO DECREASE IN INTENSITY DURING THE EVENING HOURS BEFORE WRAPPING UP 
OVERNIGHT INTO THU. NEXT OPPORTUNITY FOR PRECIP LOOKS TO BE ACROSS 
NORTHERN AREAS CHRISTMAS DAY THROUGH THE WEEKEND INTO EARLY NEXT 
WEEK. 


DAY 1 QPF (MON 20/12Z TO TUE 21/12Z): WIDESPREAD PRECIP CONTINUES 
ACROSS THE REGION. GREATEST TOTALS ARE EXPECTED ACROSS SOUTHERN CA 
FROM THE SAN GABRIEL MOUNTAINS EAST TO THE SAN BERNARDINO MOUNTAINS 
AND THEN SOUTH TO THE US/MEXICO BORDER WITH 2.00- TO 5.00-INCHES 
(LOCAL 6.00-INCHES). AT THE LOWER ELEVATIONS BETWEEN THE LA BASIN 
AND SAN DIEGO EXPECT 1.00- TO 2.00-INCHES. FOR THE REST OF THE 
HIGHER TERRAIN OF CA TOTALS WILL GENERALLY BE FROM 0.75- TO 
1.50-INCHES (LOCAL 2.00-INCHES FOR SANTA BARBARA AND VENTURA 
COUNTIES). LOWER ELEVATIONS WILL REMAIN BETWEEN 0.25- AND 0.50-INCH. 
FOR THE STATE OF NEVADA...THE SOUTHERN AND EASTERN PORTION WILL BE 
SEE THE BEST PRECIP WITH 0.25- TO 0.75-INCH (LOCAL 1.00- TO 
2.00-INCHES HIGHER TERRAIN). ELSEWHERE OVER NEVADA TOTALS WILL 
REMAIN 0.10-INCH OR LESS.

DAY 2 QPF (TUE 21/12Z TO WED 22/12Z): CONTINUED WIDESPREAD PRECIP 
WITH THE FOCUS ONCE AGAIN REMAINING ACROSS SOUTHERN CA. HIGHER 
TERRAIN WILL SEE 2.00- TO 5.00-INCHES (GREATEST FROM LOS ANGELES TO 
SAN DIEGO COUNTIES). LOWER ELEVATIONS WILL SEE 1.00- TO 2.00-INCHES. 
FOR THE REST OF THE HIGHER TERRAIN OF CA EXPECT AMOUNTS FROM 0.50- 
TO 1.00-INCH. LOWER ELEVATIONS WILL SEE 0.25- TO 0.50-INCH. ACROSS 
NEVADA...GREATEST TOTALS FOR THE SOUTHEAST PORTION OF THE STATE WITH 
0.33- TO 0.75-INCH (LOCAL 1.00- TO 2.00-INCHES HIGHER TERRAIN). 
ELSEWHERE OVER NEVADA EXPECT 0.10-INCH OR LESS.

DAY 3 QPF (WED 22/12Z TO THU 23/12Z): PRECIP WILL BEGIN TO TAPER OFF 
ALONG THE COAST NORTH OF PT CONCEPTION. HEAVIEST AMOUNTS WILL REMAIN 
OVER THE HIGHER TERRAIN FROM LOS ANGELES TO SAN DIEGO COUNTY WITH 
1.00- TO 2.50-INCHES. THE SIERRA WILL RANGE FROM 0.50-INCH NORTH TO 
JUST OVER 1.00-INCH SOUTH. FOR THE REMAINDER OF SOUTHERN CA EXPECT 
0.25- TO 0.50-INCH. FINALLY OVER SOUTHERN AND EASTERN NEVADA EXPECT 
AMOUNTS GENERALLY FROM 0.25- TO 0.50-INCH (LOCAL 1.00-INCH HIGHER 
TERRAIN). ELSEWHERE FOR THE STATE EXPECT 0.25-INCH OR LESS.


.HYDROLOGICAL CONDITIONS...

THE WET WEATHER PATTERN CONTINUES TO IMPACT RIVERS ACROSS ALL OF 
CALIFORNIA AND AREAS OF WESTERN NEVADA.  THE HEAVY RAIN IS EXPECTED 
TO CONTINUE GENERATING INCREASING RIVER FLOWS ACROSS PARTS OF 
SOUTHERN CALIFORNIA THROUGH WEDNESDAY.  MONITOR STAGES CONTINUE ON 
THE SACRAMENTO AND COSUMNES RIVERS.  A RISE PAST MONITOR STAGE 
OCCURRED ON THE SISQUOC AT GAREY YESTERDAY AFTERNOON.  A RISE ABOVE 
MONITOR IS EXPECTED BY EARLY TOMORROW MORNING ON THE SAN DIEGO RIVER 
AND A RISE NEAR FLOOD STAGE ON THE MOJAVE NEAR VICTORVILLE IS 
POSSIBLE BY WEDNESDAY.


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