MESOSCALE PRECIPITATION DISCUSSION 0358
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1153 PM EDT MON SEP 08 2014
 
AREAS AFFECTED...ERN CALIFORNIA INTO WRN NEVADA AND WRN ARIZONA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 090350Z - 090830Z
 
SUMMARY...THE FLASH FLOOD THREAT SHOULD CONTINUE FOR AT LEAST THE
NEXT 3-4 HOURS FROM ERN CALIFORNIA INTO EXTREME SRN NEVADA AND WRN
ARIZONA. LINGERING INSTABILITY OF 1000+ J/KG AND SUPPORT FROM
SEVERAL LARGER SCALE FEATURES ALLOW FOR A CONTINUED THREAT DESPITE
POOR HI-RES MODEL SUPPORT.

DISCUSSION...00Z RAOB DATA SUPPORTED RECENT SPC MESOANALYSIS
DEPICTIONS OF ML CAPE BETWEEN 500 AND 1500 J/KG FROM THE TRI-STATE
REGION OF CA/NV/AZ...SEWD INTO S-CNTRL ARIZONA. PRECIPITABLE WATER
VALUES RANGE FROM 1.5 TO 2.15 INCHES ACROSS THE THREAT
AREA...ROUGHLY 2-3 STANDARD DEVIATIONS ABOVE THE MEAN FOR EARLY
SEPTEMBER. THERE ARE MULTIPLE SOURCES OF THIS MOISTURE PER RECENT
SAB SPENES MESSAGE...AND CONTINUED ROBUST CONVECTIVE DEVELOPMENT
OVER W-CNTRL ARIZONA WITH POCKETS OF NEW DEVELOPMENT OVER THE
MOHAVE AND COLORADO DESERTS.

THE LOW LEVEL CIRCULATION ASSOCIATED WITH FORMER TROPICAL STORM
NORBERT OFF OF THE NRN BAJA PENINSULA WILL ALLOW FOR CONTINUED
SSWLY FLOW OF 20 KTS TO FUNNEL IN MOISTURE FROM THE GULF OF
CALIFORNIA INTO ERN CALIFORNIA AND WRN ARIZONA WHICH IS
PARALLELING THE MEAN STORM MOTIONS OFF TO THE NORTHEAST NEAR 15
KTS. THIS SHOULD ALLOW FOR CONTINUED BACK BUILDING OF CELLS WITHIN
THE REGION OF REMAINING CONVECTIVE INSTABILITY OVER THE NEXT 3-4
HOURS. THIS REGION IS ALSO IN A FAVORABLE REGION FOR DEVELOPMENT
BENEATH THE MID-UPPER LEVEL RIDGE AXIS OVER WRN ARIZONA.

HI-RES MODEL QPF HAS NOT HANDLED THIS SITUATION WELL THROUGH 03Z
AND SO CONFIDENCE IS A BIT REDUCED FOR THAT REASON.
HOWEVER...OBSERVATIONS SUGGEST A CONTINUED FLASH FLOOD THREAT
UNTIL AT LEAST 0800 UTC AT WHICH POINT THE SITUATION WILL BE
REASSESSED.

OTTO

ATTN...WFO...FGZ...PSR...SGX...TWC...VEF...

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

LAT...LON   36801420 36771369 36511332 35921306 34721230 
            33771128 33181123 32611157 32371204 32301252 
            32431382 32581513 32971610 34271534 35291513 
            35921495 36541466