HYDROMETEOROLOGICAL DISCUSSION NATIONAL WEATHER SERVICE / CALIFORNIA NEVADA RFC / SACRAMENTO CA 930 AM PST TUE DEC 21 2010 ...HEAVY PRECIP PERSISTS FROM SOCAL TO SE NEV... ...WIDESPREAD PRECIP WITH APPROACHING SYSTEM TONIGHT INTO WED... .24 HOUR PRECIPITATION TOTALS (ENDING DEC 21 AT 400 AM PST)... A LONG FETCH OF TROPICAL MOISTURE AFFECTED PORTIONS OF SOUTHERN CA NE ACROSS DESERT LOCATIONS UP INTO SOUTHERN AND EXTREME EASTERN NEV. FARTHER NORTH IN THE COOLER AIRMASS...SCATTERED PRECIP AFFECTED THE NORTHERN HALF OF THE REGION. GREATEST TOTALS WERE RECORDED OVER THE EASTERN SAN GABRIEL AND WESTERN SAN BERNARDINO MOUNTAINS WITH 4.00- TO 8.00-INCHES. THERE WERE A FEW LOCATIONS THAT SURPASSED THE 10.00-INCH MARK IN THE SAN BERNARDINO MOUNTAINS AROUND THE BIG BEAR AREA. FOR OTHER MOUNTAINOUS AREAS OF EXTREME SOUTHERN CA...THE SANTA ANA MOUNTAINS WERE NEXT IN LINE WITH 3.00- TO 6.00-INCHES WITH THE SAN JACINTO AND LAGUNA MOUNTAINS RIGHT BEHIND WITH 2.00- TO 4.00-INCHES. COASTAL LOCATIONS BETWEEN LOS ANGELES AND SAN DIEGO WERE IN THE RANGE OF 0.75- TO NEARLY 2.00-INCHES (GREATEST AROUND ORANGE COUNTY). THE HEAVY PRECIP SPILLED OVER THE SE CA DESERTS WITH WIDESPREAD AMOUNTS BETWEEN 0.75- TO 1.50-INCHES. THE MAJORITY OF THIS PRECIP WAS ALONG THE I-15 CORRIDOR. CLOSER TO THE LOWER COLORADO RIVER THE PRECIP WAS LIMITED TO LIGHTER AMOUNTS OF 0.25-INCH OR LESS. EVENTUALLY THE MOISTURE MADE ITS WAY INTO SOUTHERN AND EASTERN NEVADA. THE SPRING MOUNTAINS AND GRANT RANGE WERE THE WINNERS IN TERMS OF AMOUNTS WITH 2.00- TO 4.00-INCHES (LOCAL 5.00-INCHES). OTHERWISE TOTALS OF 0.75- TO 1.50-INCHES WERE WIDESPREAD OVER THIS AREA. THE SOUTHERN SIERRA TO THE TEHACHAPIS WERE AT THE NORTHERN FRINGE OF THE HIGHER MOISTURE CONTENT AIR AND SAW TOTALS FROM 0.75- TO 2.00-INCHES. THERE WERE EVEN A FEW LOCATIONS IN THE TEHACHAPIS THAT REACHED CLOSE TO 3.00-INCHES. FOR THE REST OF THE SIERRA...PRECIP VARIED GREATLY WITH PEAK VALUES OVER THE FEATHER RIVER BASIN WITH 1.00- TO 2.00-INCHES. HOWEVER...CLOSER TO THE AMERICAN RIVER BASIN AND JUST TO THE SOUTH TOTALS WERE MUCH LESS NEAR A 0.25-INCH OR LESS. THE NW PORTION OF THE STATE...INCLUDING THE SHASTA DRAINAGE SAW TOTALS GENERALLY BETWEEN 0.50- AND 1.50-INCHES. GREATEST TOTALS WERE IN THE WESTERN PORTION OF THE SHASTA DRAINAGE AND THE SMITH RIVER BASIN WHERE A FEW LOCATIONS TOPPED OUT NEAR 2.00-INCHES. FOR THE CENTRAL CA COAST DOWN SOUTH TOWARD PT CONCEPTION AMOUNTS VARIED WITH THE LIGHTEST TOTALS IN THE NORTH AND HEAVIEST IN THE SOUTH. OVER MONTEREY COUNTY PRECIP WAS IN THE RANGE OF 0.10- TO 0.25-INCH (LOCAL 0.50-INCH FOR THE BIG SUR COAST). SOUTH ACROSS SAN LUIS OBISPO AND SANTA BARBARA COUNTIES TOTALS WERE IN THE RANGE OF 0.50-INCH NORTH TO 1.25-INCHES SOUTH. FINALLY FOR THE CENTRAL VALLEY...TOTALS VARIES WITH THE BEST AMOUNTS SOUTH NEAR BAKERSFIELD AND FRESNO WITH 0.50-INCH. THERE WAS A LOCALIZED HEAVIER AMOUNT IN VISALIA...WHICH TOPPED 1.00-INCH. ELSEWHERE OVER THE CENTRAL VALLEY AMOUNTS REMAINED NEAR 0.25-INCH OR LESS. .METEOROLOGICAL CONDITIONS... FETCH OF MOISTURE STREAMING FROM SW-TO-NE CONTINUES TO IMPACT COASTAL SECTIONS OF SOUTHERN CA FROM THE LA BASIN TO THE US/MEXICO BORDER BEFORE ADVECTING INLAND AND IMPACTING THE COASTAL MOUNTAINS AND FARTHER REACHES OF THE SE CA DESERTS INTO SOUTHERN/EXTREME EASTERN NEV. THIS FEATURE HAS MOVED VERY LITTLE OVER THE PAST 18 HOURS...AFFECTING SIMILAR AREAS WITH MODERATE TO HEAVY PRECIP. AMSU TPW PASSES FROM OVERNIGHT SHOW AVAILABLE MOISTURE CONTINUES TO RANGE FROM 1.00- TO 1.25-INCHES. MEANWHILE...THE GPS-MET SENSORS ALONG THE SAN DIEGO COUNTY COAST AT POINT LOMA AND LA JOLLA ARE SHOWING A SIMILAR IPW READING. FARTHER INLAND...THE ESSEX GPS-MET SENSOR IS SHOWING THE TREMENDOUS AMOUNT OF MOISTURE BEING ADVECTED INLAND WITH AN IPW HOVERING AT THE 1.00-INCH MARK. FOR THE 21/12Z KNKX RAOB...SATURATION IS STILL IN A LAYER BETWEEN THE SFC AND ALMOST 700-MB. AVAILABLE MOISTURE HAS REMAINED VERY CONSTANT OVER THE PAST 24-HOURS WITH A RECORDED PW OF 1.08-INCHES (APPROX 225-PERCENT OF NORMAL). WINDS IN THE LOW-LEVELS ARE TURNING A BIT MORE TOWARD A SOUTHERLY DIRECTION AS THE OFFSHORE UPR TROF ALONG 130W DIGS TOWARD THE SOUTH. HOWEVER...FROM ABOUT 700-MB AND FARTHER UP IN THE ATMOSPHERE WINDS VEER TO A SWLY DIRECTION. OVERALL...ONSHORE FLOW IS A BIT WEAKER..AND THIS IS RESULTING IN PRECIP TOTALS LESS THAN WHAT WAS BEING EXPERIENCED YESTERDAY LATE AFTERNOON AND EVENING. FOR THE NEXT 12 HOURS OR SO...LOOK FOR A SIMILAR SCENARIO. THE MOISTURE PLUME WILL GO THROUGH ONLY SLIGHT ALTERATIONS...BUT REMAIN FOCUSED OVER SIMILAR AREAS. EXPECTED PRECIP AMOUNTS FOR THE AFTERNOON AND EVENING PERIODS WILL BE SIMILAR TO WHAT IS CURRENTLY OCCURRING. JUST OFF THE NORTHERN AND CENTRAL CA COAST THERE IS QUITE A BIT OF CONVECTIVE ACTIVITY STREAMING FROM S-TO-N...JUST AHEAD OF THE COLD FRONT. NLDN HAS SHOWN STRIKES WITH SEVERAL OF THESE BANDS OF PRECIP. 21/12Z GFS DEPICTS THIS AREA OF LOWERED STABILITY QUITE WELL WITH LIFTED INDICES DOWN NEAR OR JUST BELOW 0-DEG C. BEST BL CAPE IS SITUATED FROM JUST OFF PT ARENA SOUTH ALONG THE BOUNDARY WITH VALUES IN UPWARDS OF 200-J/KG. SO FAR...ONLY LIGHT AMOUNTS OF PRECIP HAVE MADE THEIR WAY ONSHORE. HOWEVER...LOW-LEVEL SOUTHERLY FLOW THROUGH THE SACRAMENTO VALLEY IS GENERATING SOME DECENT CONVERGENCE OVER THE SHASTA DRAINAGE WITH SOME WIDESPREAD AMOUNTS BETWEEN 0.10- AND 0.25-INCH SINCE 21/12Z. MODELS FOR THE MOST PART CONTINUE TO SHOW THE UPR TROF SLOWLY SHIFTING OFF TOWARD THE EAST TODAY...AND SPLITTING. THE NORTHERN S/WV TROF WILL MOVE ACROSS NORTHERN CA...WHILE THE STRONG SOUTHERN SYSTEM TAKES AIM AT THE SOUTHERN THIRD OF THE REGION. PRECIP WILL BEGIN TO PICK UP ALONG COASTAL SECTIONS FROM NEAR PT CONCEPTION NORTHWARD TO THE CA/ORE BORDER DURING THE LATER EVENING HOURS. INCREASING SOUTHERLY FLOW IN THE LOW-LEVELS WILL RESULT IN UPSLOPE CONDITIONS FOR THE SANTA YNEZ TO SAN RAFAEL MOUNTAINS WITH ALL THE MODELS INDICATING THE DEVELOPMENT OF MODERATE PRECIP IN THIS AREA. INTO THE OVERNIGHT HOURS...THE UPR TROF AXIS WILL BE JUST OFF THE NORTHERN AND CENTRAL CA COAST. WITH THE FLOW JUST AHEAD OF THE COLD FRONT BEING SOUTHERLY...THIS IS NOT IDEAL FOR OROGRAPHICALLY INDUCED PRECIP. MUCH OF THE PRECIP WILL BE ASSOCIATED WITH THE COLD FRONT AS IT SWINGS INLAND WEDNESDAY MORNING. FARTHER SOUTH ACROSS SOUTHERN CA...ONSHORE FLOW WILL INCREASE WITH DYNAMICS BECOMING MORE FAVORABLE WITH A STRONG MID-LEVEL VORT MAX AT THE BASE OF THE SYSTEM. EXPECT PRECIP TO RAMP UP DURING THE OVERNIGHT HOURS AND PEAK DURING THE MORNING HOURS ALONG THE COAST FROM PT CONCEPTION TO THE US/MEXICO BORDER. ALSO...CONVECTIVE ACTIVITY WILL ONLY ADD TO THE MIX FOR THE POTENTIAL OF HEAVY PRECIP. LIFTED INDICES OFFSHORE DROP TO NEARLY MINUS 4-DEG C WITH VALUES INLAND JUST ABOUT REACHING MINUS 1-DEG C. CAPES WILL BE ON THE ORDER OF 250-J/KG AS THE SYSTEM MOVES INLAND. SO...WITH THE LOWERED STABILITY...T-STORMS LOOK TO BE A DEFINITE. MOISTURE TRANSPORT INLAND ACROSS THE SE CA DESERTS TOWARD SOUTHERN AND EASTERN NEV ONCE AGAIN LOOKS GOOD FOR MODERATE TO LOCALLY HEAVY PRECIP. PRECIP AMOUNTS WERE ADJUSTED ACCORDINGLY TO ACCOUNT FOR THIS SCENARIO. FINALLY BY THURSDAY...THE SYSTEM WILL EXIT TO THE EAST. THIS WILL SHUNT THE BEST MOISTURE TO THE SOUTH AND EAST...LEAVING THE REGION DRY UNDER NWLY FLOW ALOFT. THIS WILL LAST INTO FRIDAY...UNTIL A SYSTEM TAKES AIM AT THE NORTHERN HALF OF THE REGION FOR CHRISTMAS DAY. DAY 1 QPF (TUE 21/12Z TO WED 22/12Z): WIDESPREAD PRECIP WILL AFFECT THE REGION. GREATEST TOTALS WILL FALL OVER THE HIGHER TERRAIN FROM THE EASTERN SAN GABRIEL MOUNTAINS TO THE SAN BERNARDINO MOUNTAINS...AS WELL AS SOUTH ACROSS THE LAGUNA MOUNTAINS WITH 2.00- TO 4.00-INCHES (LOCAL 5.00-INCHES). REST OF THE HIGHER TERRAIN OF SOUTHERN CA WILL SEE 1.50- TO 3.00-INCHES. COASTAL LOCATIONS CAN EXPECT 1.00- TO 2.00-INCHES. PRECIP WILL SPILL ACROSS THE SE CA DESERTS NE TOWARD SOUTHERN AND EXTREME EASTERN NEV WITH 0.25- TO 0.75-INCH (HIGHER TOTALS FOR THE SPRING MOUNTAINS WITH 1.00- TO 2.00-INCHES). FOR THE REST OF THE HIGHER TERRAIN OF NORTHERN AND CENTRAL CA EXPECT 0.50- TO 1.00-INCH (LOCAL 1.50-INCHES NW PORTION OF THE STATE). LOWER ELEVATIONS WILL SEE 0.10- TO 0.25-INCH AMOUNTS (LOCAL 0.50-INCH ALONG THE COAST). FOR THE NORTHERN AND WESTERN PORTIONS OF NEV EXPECT AMOUNTS TO HOVER BETWEEN DRY AND 0.10-INCH. DAY 2 QPF (WED 22/12Z TO THU 23/12Z): WIDESPREAD PRECIP CONTINUES WITH THE GREATEST AMOUNTS OVER THE HIGHER TERRAIN OF SOUTHERN CA WITH 1.50- TO 4.00-INCHES (GREATEST FOR THE EASTERN SAN GABRIEL...WESTERN SAN BERNARDINO...AND LAGUNA MOUNTAINS). COASTAL LOCATIONS OF SOUTHERN CA WILL SEE TOTALS NEAR 1.00-INCH. PRECIP WILL ONCE AGAIN SPILL OVER THE SE CA DESERTS TOWARD SOUTHERN AND EXTREME EASTERN NEV WITH 0.25- TO 0.75-INCH (HIGHER TOTALS OVER THE SPRING MOUNTAINS WITH 1.00- TO 2.50-INCHES). FOR THE LENGTH OF THE SIERRA TOTALS WILL RANGE FROM 0.75-INCH NORTH TO 1.25-INCHES SOUTH. ELSEWHERE...EXPECT AMOUNTS TO REMAIN NEAR OR LESS THAN 0.25-INCH. DAY 3 QPF (THU 23/12Z TO FRI 24/12Z): FINALLY AN END...DRY! .HYDROLOGICAL CONDITIONS... MODERATE TO HIGH RIVER FLOWS CONTINUE TO IMPACT MOST AREAS OF CALIFORNIA. THE MOST EXTREME FLOW CONDITIONS ARE OCCURRING IN SOUTHERN CALIFORNIA THIS MORNING. FLOOD STAGES HAVE OCCURRED ON THE MOJAVE AND SANTA MARGARITA RIVERS AND IS POSSIBLE ON THE SAN DIEGO RIVER. MANY SMALLER STREAMS ARE ALSO OUT OF THEIR BANKS IN THOSE AREAS. ELSEWHERE ACROSS THE STATE THE SACRAMENTO RIVER IS GENERATING WEIR FLOW AT TISDALE AND FREMONT WEIRS THIS MORNING. THE COSUMNES RIVER REMAINS ABOVE MONITOR LEVELS AT SOME LOCATIONS. THE HEAVY RAIN WILL CONTINUE TO PRODUCE HIGH WATER CONDITIONS ON MANY SOUTHERN CALIFORNIA RIVERS AND STREAMS THROUGH WEDNESDAY. MORE INFORMATION ON THE CNRFC WEBSITE AT HTTP://WWW.CNRFC.NOAA.GOV DRK/AM