MESOSCALE PRECIPITATION DISCUSSION 0552
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
326 PM EDT SUN OCT 04 2015
 
AREAS AFFECTED...PORTIONS OF SOUTHEAST CA/SOUTHWEST NV 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 041926Z - 050126Z
 
SUMMARY...CONVECTIVE DEVELOPMENT CONTINUES NEAR A DEEP CYCLONE
ACROSS SOUTHWEST CA.  WITH LOCAL AMOUNTS OF ~1.5" EXPECTED IN AN
ARID REGION, FLASH FLOODING/DEBRIS FLOWS ARE POSSIBLE.

DISCUSSION...SATELLITE IMAGERY HAS SHOWN CONVECTIVE ENHANCEMENT
AROUND AN DEEP-LAYERED LOW ACROSS SOUTHWEST CA.  OBSERVATIONS FROM
TONOPAH NV, WITHIN A RADAR COVERAGE GAP, INDICATE 1.17" OF RAIN
HAS FALLEN OVER THE PAST SIX HOURS, BEYOND THE 10 YEAR RECURRENCE
INTERVAL.  PRECIPITABLE WATER VALUES ARE 0.75-1", SUFFICIENT FOR
HEAVY RAIN ISSUES WITHIN AREAS OF TERRAIN.  THE FLOW IS
UNIDIRECTIONAL OUT OF THE SOUTH, IMPLYING CELL TRAINING WOULD BE
THE MAIN FLASH FLOOD THREAT, WITH 700 HPA/CLOUD BASE INFLOW OF
20-30 KTS PER VAD WIND PROFILES AND RAP MASS FIELD FORECASTS. 
MLCAPES ARE ROUGHLY 500 J/KG, AND SHOW AN INCREASING TREND WITHIN
SPC MESOANALYSES NEAR THE NV/CA/AZ BORDER JUNCTION.

CAM GUIDANCE SUGGESTS LOCAL AMOUNTS OF 1-2" ARE POSSIBLE THROUGH
01Z AS AVAILABLE INSTABILITY AND LOW-LEVEL INFLOW INCREASES INTO
THE EVENING HOURS.  THESE AMOUNTS WOULD REACH THE ONCE IN 25 YEAR
RECURRENCE INTERVAL, STRONGLY SUGGESTING A FLASH FLOOD RISK.  THE
THREE HOUR NEIGHBORHOOD PROBABILITIES FOR EXCEEDING THE FLASH
FLOOD GUIDANCE VALUES SUGGEST A RISK THROUGH 02Z, SO USED A SIX
HOUR WINDOW.  FLASH FLOODING, WITH ASSOCIATED DEBRIS FLOWS, ARE
POSSIBLE WITHIN THESE NORMALLY ARID AREAS.

ROTH

ATTN...WFO...HNX...LKN...REV...STO...VEF...

ATTN...RFC...CBRFC...CNRFC...

LAT...LON   39551877 39181672 37641509 35661534 35101622 
            35991720 36021737 36021783 36141806 35691811 
            35621806 35171881 36201906 37781983 38912031