HYDROMETEOROLOGICAL DISCUSSION NATIONAL WEATHER SERVICE / CALIFORNIA NEVADA RFC / SACRAMENTO CA 930 AM PST SUN DEC 19 2010 ...WIDESPREAD MODERATE TO HEAVY PRECIP CONTINUES REGION-WIDE... ...MAJOR SOUTHERN CA PRECIP EVENT POSSIBLE THROUGH WEDNESDAY... .24 HOUR PRECIPITATION TOTALS (ENDING DEC 19 AT 400 AM PST)... WIDESPREAD PRECIP WAS RECORDED ACROSS THE REGION AS A STRONG COLD FRONT MOVED ACROSS THE REGION BEFORE STALLING ACROSS THE SOUTHERN SIERRA BACK TOWARD PT CONCEPTION. THE NEXT WAVE OF PRECIP STARTED MOVING IN OVERNIGHT ALONG COASTAL LOCATIONS. GREATEST TOTALS WERE RECORDED OVER THE SOUTHERN SIERRA WITH 3.00- TO 6.00-INCHES THE NORM. HOWEVER...THERE WERE A FEW LOCATIONS OVER THE HIGHEST PEAKS THAT RECORDED APPROX 10.00-INCHES OF LIQUID EQUIVALENT. FOR THE NORTHERN SIERRA...AMOUNTS WERE A BIT LIGHTER THAN THE COUNTERPARTS TO THE SOUTH. HOWEVER...AMOUNTS WERE STILL QUITE HIGH WITH 2.00- TO 4.00-INCHES. ALONG COASTAL SECTIONS...GREATEST AMOUNTS WERE OBSERVED FROM SAN LUIS OBISPO COUNTY SOUTH ACROSS SANTA BARBARA COUNTY BEFORE REACHING VENTURA COUNTY. AMOUNTS WERE IN THE RANGE OF 2.00- TO 4.00-INCHES WITH A FEW LOCATIONS REACHING OR JUST SURPASSING 5.00-INCH ACROSS SOUTHWEST SAN LUIS OBISPO COUNTY. THE REST OF THE CENTRAL CA COAST SAW TOTALS OF 1.00- TO 2.50-INCHES OVER THE SANTA CRUZ MOUNTAINS AND 1.00- TO 3.00-INCHES ACROSS THE SANTA LUCIA MOUNTAINS (GREATEST ALONG THE BIG SUR COAST). THE NORTH COAST AND SHASTA DRAINAGE RANGED FROM 0.50- TO 1.25-INCHES ACROSS MOST LOCATIONS. HOWEVER...OVER THE SMITH RIVER BASIN SLIGHTLY HIGHER NUMBERS WERE RECORDED WITH TOTALS FROM 2.00- TO 3.00-INCHES. CENTRAL VALLEY LOCATIONS VARIED GREATLY WITH LIGHTEST TOTALS UP ACROSS THE NORTHERN SACRAMENTO VALLEY WHERE AMOUNTS WERE BETWEEN 0.25- AND 0.50-INCH. FROM SACRAMENTO SOUTH TOWARD BAKERSFIELD TOTALS RANGED FROM 0.50- TO 2.00-INCHES. IN FACT...SEVERAL SAN JOAQUIN VALLEY STATIONS SAW RECORD DAILY RAINFALL FOR THE DAY. BAKERSFIELD ENDED UP THE 24-HOUR PERIOD WITH 1.67-INCHES. FOR THE STATE OF NEVADA...AMOUNTS WERE GREATEST NORTH AND WEST WITH THE HIGHER TERRAIN SEEING 0.25- TO 0.75-INCH. AMOUNTS SURPASSING 1.00-INCH WERE OBSERVED CLOSER TO THE CA BORDER WITH THE EAST SIERRA FOOTHILLS. LOWER ELEVATIONS FOR THE MOST PART STAYED FROM 0.25-INCH OR LESS. THE SOUTHEAST PORTION OF NEVADA SAW LOWER ELEVATIONS AT OR BELOW 0.10-INCH...WHILE THE HIGHER TERRAIN REACHED CLOSER TO 0.25-INCH. .METEOROLOGICAL CONDITIONS... WV/IR IMAGERY INDICATES A STRONG S/WV TROF CURRENTLY CROSSING 130W...ON ITS PATH TOWARD THE SOUTHERN ORE AND NORTHERN CA COAST. THIS FEATURE IS ROTATING AROUND THE DEEP POLAR UPR LOW SITUATED OFFSHORE NEAR 44N/134W. IMPRESSIVE MOISTURE TAP CONTINUES BACK ESE TOWARD AN AREA JUST NORTH AND WEST OF HAWAII. AMSU TPW PASSES FROM OVERNIGHT SHOW THIS LONG FETCH AIMED AT THE CENTRAL AND SOUTHERN CA COAST WITH PEAK VALUES JUST SHY OF 1.50-INCHES. 19/12Z KVBG AND KOAK ROABS SHOW SATURATION THROUGH MUCH OF THE COLUMN AND A PW VALUE OF 1.19- AND 1.06-INCHES RESPECTIVELY. THIS IS SOMEWHERE BETWEEN 200- AND 250-PERCENT OF NORMAL FOR THIS TIME OF YEAR. WINDS IN THE PROFILE START FROM THE DUE SOUTH BEFORE VEERING TO THE SOUTHWEST IN THE MID-LEVELS AND EVENTUALLY WSW FARTHER UP IN THE ATMOSPHERE. 88-D DATA SHOWS WIDESPREAD PRECIP MOVING ACROSS THE REGION WITH SEVERAL POCKETS OF HEAVY PRECIP. ONE AREA NOT REPRESENTED WELL BY RADAR IS THE TRANSVERSE MOUNTAINS OF SOUTHERN CA. AS THE SFC LOW ASSOCIATED WITH THE S/WV TROF HAS MOVED CLOSER TO THE PACNW AND MATURES...THE SOUTHERLY MSLP GRADIENT HAS TIGHTENED CONSIDERABLY OVERNIGHT. COASTAL BUOYS FROM JUST OFF THE SANTA BARBARA AND VENTURA COUNTY COAST INDICATES WINDS GUSTING TO NEARLY 25-MPH FROM THE DUE SOUTH...WHICH IS PROVIDING AMPLE UPSLOPE CONDITIONS TO TAKE ADVANTAGE OF THE COPIOUS AMOUNT OF MOISTURE AVAILABLE WITHIN THE MOISTURE PLUME. SINCE 19/12Z...PLENTY OF PRECIP GAGES OVER THE SANTA YNEZ AND SAN RAFAEL MOUNTAINS ARE INDICATING TOTALS PASSING 1.50-INCHES AND BEGINNING TO REACH 2.00-INCHES. THIS WILL CONTINUE OVER THE NEXT 6 TO 9 HOURS UNTIL THE COLD FRONT PASSES AND THE MSLP GRADIENTS WEAKEN. FARTHER NORTH...THE PRECIP BAND ASSOCIATED WITH THE COLD FRONT HAS MOVED ACROSS THE SF BAY AREA AND PORTIONS OF THE CENTRAL CA COAST. HEAVIEST PRECIP IN THIS AREA IS NOW SHIFTING ACROSS THE CENTRAL VALLEY...ON ITS WAY TOWARD THE LENGTH OF THE SIERRA. QUITE AN IMPRESSIVE AMOUNT OF PRECIP IN THE BAY AREA SINCE 19/12Z AS WELL...WITH GAGES SOUTH OF THE GOLDEN GATE REPORTING 0.75- TO 1.25-INCHES. HOWEVER...ACROSS THE SANTA CRUZ MOUNTAINS THERE ARE A FEW GAGES ALREADY SURPASSING THE 2.00-INCH MARK. THROUGH THE REST OF TODAY...AS THE S/WV TROF MOVES INLAND ACROSS SOUTHERN ORE AND NORTHERN CA...EXPECT PRECIP TO FOCUS ALONG THE ENTIRE LENGTH OF THE SIERRA. UPSLOPE CONDITIONS WILL BE IDEAL WITH 700-MB WINDS FROM THE SW PEAKING IN THE RANGE OF 45- TO 65-KT. ALONG WITH THE ADDED DYNAMICS FROM THE PASSING COLD FRONT...EXPECT IMPRESSIVE PRECIP TOTALS THROUGH THE 20/00Z TIME PERIOD. INTO THE EVENING HOURS...AS THE SYSTEM PRESSES INLAND...THE UPR JET WILL SAG TOWARD THE SOUTH AND THE MOISTURE PLUME WILL BE SHUNTED FARTHER SOUTH...FOCUSING PRIMARILY OVER SOUTHERN CA. ALTHOUGH MOISTURE WILL BE LESS ACROSS THE SOUTHERN SIERRA...STRONG UPSLOPE FLOW WILL CONTINUE ANOTHER MODERATE PERIOD OF PRECIP. THE FRONTAL BOUNDARY WILL STALL OUT ACROSS SOUTHERN CA...PROVIDING A FOCUSING MECHANISM FOR THE MODERATE TO HEAVY PRECIP BETWEEN THE EASTERN SAN GABRIEL MOUNTAINS INTO THE SAN BERNARDINO MOUNTAINS. WITH MOISTURE ON THE INCREASE ACROSS SAN DIEGO COUNTY...PRECIP WILL BEGIN TO PICK UP AS WELL AS WESTERLY MID-LEVEL FLOW WILL PROVIDE FOR ADDED OROGRAPHICS. THE 20/00Z TO 20/06Z PERIOD LOOKS TO BE THE BEST FOR PRECIP PRODUCTION ACROSS THIS AREA...UNTIL THE BIGGER SHOW ENTERS THE PICTURE FOR LATER MONDAY INTO TUESDAY. WITH THE OFFSHORE UPR TROF DEEPENING ALONG 130W...THIS WILL DRAW ANOTHER SURGE OF HIGH MOISTURE CONTENT AIR TOWARD THE SOUTHERN CA COAST. MODELS HAVE BECOME MUCH BETTER ALIGNED IN SHOWING THIS NEXT MOISTURE PLUME INTERACTING WITH THE COAST FROM NEAR THE LA BASIN SOUTH TOWARD THE US/MEXICO BORDER. THE GFS HAS BEEN CONSISTENT IN SHOWING PW VALUES WITHIN THIS FEATURE JUST SHY OF 1.50-INCHES. ONSHORE FLOW WILL CONTINUE TO FEED MOISTURE OVER THE REGION WITH GOOD UPSLOPE CONDITIONS FOR OROGRAPHICALLY ENHANCED PRECIP. FOR THE LATER MONDAY INTO TUESDAY PERIOD...THE 19/00Z GFS-BASED OROGRAPHIC AID CONTINUES TO HIT THE SAN GABRIEL MOUNTAINS EAST TOWARD THE SAN BERNARDINO MOUNTAINS...AND THEN SOUTH ACROSS SAN DIEGO COUNTY WITH IMPRESSIVE TOTALS. FOR THE 48-HOUR TIME PERIOD ENDING 22/12Z...THIS AID SHOWS 6.00- TO 12.00-INCHES. GIVEN THE PROLONGED PERIOD OF THE MOISTURE PLUME INTERACTING WITH THE COAST IN THIS AREA...THESE NUMBERS DO NOT SEEM OUT OF BOUNDS AT ALL. DEFINITELY WILL NEED TO KEEP MONITORING THIS SITUATION AS THESE TYPE OF TOTALS ACROSS SOUTHERN CA WOULD CERTAINLY LOOK TO CAUSE SOME PROBLEMS. FARTHER NORTH FOR THE DAY 2 AND 3 TIME PERIOD. A S/WV TROF MOVING THROUGH THE WSW FLOW ALOFT WILL BRING AN UPTICK TO PRECIP FOR THE FIRST HALF OF MONDAY...FOLLOWED BY A 12-HOUR PERIOD OF LIGHTER PRECIP DURING THE EVENING AND OVERNIGHT HOURS. INTO TUESDAY...THE DIGGING UPR TROF WILL APPROACH THE COAST FOR ANOTHER ROUND OF PRECIP THAT WILL LAST INTO THE FIRST HALF OF WEDNESDAY. SNOW LEVELS ARE BEGINNING TO DROP BEHIND THE FRONT WITH SNOW NOW BEING REPORTED AT BLUE CANYON ALONG THE I-80 CORRIDOR (5280-FEET ELEVATION). TEMPERATURES HAVE BEEN SLOWLY DECREASING THIS MORNING...ABOUT 1-DEG F PER HOUR IN MOST LOCATIONS NEAR THE FRONT. AHEAD OF THE FRONT...THERE HAS BEEN SOME SLIGHT WARMING...BUT NOT OVERLY DRAMATIC. DAY 1 QPF (SUN 19/12Z TO MON 20/12Z): WIDESPREAD PRECIP CONTINUES ACROSS THE REGION. HEAVIEST AMOUNTS ALONG THE LENGTH OF THE SIERRA AND THE TRANSVERSE RANGES OF SOUTHERN CA WITH 2.00- TO 5.00-INCHES (LOCAL TOTALS TO 6.00-INCHES). THE OTHER HOT SPOT WILL BE THE CENTRAL CA COAST AND THE MOUNTAINS RIVERSIDE TO SAN DIEGO COUNTY WITH 1.00- TO 3.00-INCHES. ELSEWHERE OVER THE HIGHER TERRAIN OF CA...EXPECT 0.75- TO 1.50-INCHES (LOCAL 2.00-INCHES). LOWER ELEVATIONS WILL RANGE FROM 0.50- TO 1.50-INCHES (GREATEST SOUTHERN SACRAMENTO AND ENTIRE SAN JOAQUIN VALLEY). FOR NEVADA...HIGHER TERRAIN WILL SEE 0.50- TO 1.00-INCH WITH 0.25- TO 0.50-INCH LOWER ELEVATIONS. HIGHER TOTALS CAN BE EXPECTED OVER FAR WESTERN NEVADA NEAR THE EAST SIERRA. DAY 2 QPF (MON 20/12Z TO TUE 21/12Z): WIDESPREAD PRECIP CONTINUES ACROSS THE REGION. GREATEST AMOUNTS WILL FALL OVER THE HIGHER TERRAIN OF SOUTHERN CA WITH 2.50- TO 5.00-INCHES (LOCAL 6.00-INCHES). THE SIERRA WILL RANGE FROM 1.00- TO 2.00-INCHES (GREATEST SOUTH). ELSEWHERE OVER THE HIGHER TERRAIN OF CA EXPECT 0.75- TO 1.50-INCHES. FOR LOWER ELEVATIONS...AMOUNTS WILL VARY WITH LIGHTEST AMOUNTS NORTH AND GREATEST SOUTH. FOR THE CENTRAL VALLEY EXPECT 0.25- TO 0.50-INCH. FOR SOUTHERN CA EXPECT 1.00- TO 2.00-INCHES. ACROSS NEVADA...GREATEST AMOUNTS WILL BE SOUTH AND EAST WITH 0.50- TO 1.25-INCHES HIGHER TERRAIN AND 0.25- TO 0.50-INCH LOWER ELEVATIONS. ACROSS THE NORTH AND WEST AMOUNTS WILL GENERALLY BE NEAR OR LESS THAN 0.25-INCH. DAY 3 QPF (TUE 21/12Z TO WED 22/12Z): SAME STORY WITH WIDESPREAD PRECIP ACROSS THE REGION. GREATEST TOTALS CONTINUE OVER SOUTHERN CA. HIGHER TERRAIN CAN EXPECT 2.00- TO 5.00-INCHES (LOCAL 6.00-INCHES). LOWER ELEVATIONS ALONG THE COAST WILL SEE 1.00- TO 2.00-INCHES. ELSEWHERE OVER THE HIGHER TERRAIN OF CA TOTALS WILL GENERALLY BE FROM 0.50- TO 1.00-INCH (GREATEST NORTH COAST AND SOUTHERN SIERRA). FOR NEVADA...EXPECT GREATEST TOTALS ONCE AGAIN SOUTH AND EAST WITH 0.75- TO 1.50-INCHES HIGHER TERRAIN (LOCAL TO 2.00-INCHES). LOWER ELEVATIONS CAN EXPECT 0.25- TO 0.75-INCH. ELSEWHERE IN THE STATE TOTALS WILL REMAIN NEAR OR LESS THAN 0.25-INCH. .HYDROLOGICAL CONDITIONS... AREAS OF HEAVY PRECIPITATION CONTINUE TO GENERATE INCREASING FLOWS ON MOST RIVERS ACROSS CALIFORNIA AND PARTS OF WESTERN NEVADA. RIVERS WITH CURRENT OR FORECAST STAGES ABOVE MONITOR LEVEL INCLUDE THE SACRAMENTO, COSUMNES, TUOLUMNE AND SAN DIEGO. MANY SMALLER STREAMS ARE AT BANKFULL AND BEYOND. THE HIGHER FLOWS ARE EXPECTED TO CONTINUE FOR THE NEXT FEW DAYS AS THE WET WEATHER PATTERN CONTINUES. 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