MESOSCALE PRECIPITATION DISCUSSION 0446
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
401 PM EDT THU AUG 13 2015
 
AREAS AFFECTED...SOUTHERN NV, NORTHWEST AZ, AND VICINITY 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 132000Z - 140000Z
 
SUMMARY...DEVELOPING THUNDERSTORMS WITHIN A MOISTURE CHANNEL ARE
SHOWING SLOW MOVEMENT WHILE INCREASING IN COVERAGE.  FLASH
FLOODING IS POSSIBLE.

DISCUSSION...A MOISTURE CHANNEL SEEN ON WATER VAPOR IMAGERY ACROSS
THE REGION EXISTS ON THE WEST SIDE OF A SUBTROPICAL RIDGE WHICH
HAS BEEN SLOWLY RETROGRADING OVER THE PAST COUPLE DAYS.  A VAGUE,
WEAK SHORTWAVE LEFT OVER FROM LAST NIGHT'S CONVECTION IN SOUTHWEST
AZ IS MOVING INTO THE SCENE FROM THE SOUTH-SOUTHEAST. 
PRECIPITABLE WATER VALUES OF 1-1.7" EXIST HERE, WHICH ARE 2-3
SIGMAS ABOVE THE MEAN FOR MID-AUGUST.  CLOUD BASE INFLOW OF 10-15
KTS IS SEEN AT 700 HPA PER RECENT RAP FORECASTS AND VAD WIND
PROFILES NEAR AND WEST OF THIS REGION, WHICH COULD ORGANIZE
CONVECTION ABOVE THE PULSE MODE.  CELL MOTION HAS BEEN ROUGHLY
NORTH AT 5-10 KTS, ALONG THE MAGNITUDE OF THE MEAN 850-400 HPA
WIND.  MLCAPES IN THE AREA ARE 1000-2000 J/KG IN THIS AREA.

IF CELLS ARE ABLE TO FURTHER ORGANIZE, THEY COULD PICK UP THE PACE
TO NORTH AT 15 KTS.  OTHER ACTIVITY COULD FIRE NEAR THE AZ/CA
BORDER ONCE CIN ERODES FURTHER.  CELL MERGERS/TRAINING APPEAR TO
BE THE MAIN FLASH FLOOD THREAT.  CONSIDERING THE MOISTURE
AVAILABILITY, HOURLY RAIN RATES UP TO 1.5" ARE POSSIBLE.  MOST OF
THE CAM GUIDANCE IS USELESS IN THIS REGION.  THE MAIN EXCEPTION IS
THE 12Z SPC WRF, WHICH ADVERTISES LOCAL AMOUNTS OF 2-3" ACROSS
SOUTHERN NV, WHICH SEEMS REASONABLE.  THIS DEGREE OF RAINFALL
COULD LEAD TO FLASH FLOODING/DEBRIS FLOWS ACROSS THE AREA.  THE
AVAILABLE INSTABILITY SUPPORTS ABOUT FOUR HOURS OF ACTIVE
CONVECTION BEFORE THE ATMOSPHERE STABILIZES, SO USED THAT AS THE
HORIZON FOR THIS MPD.

ROTH

ATTN...WFO...FGZ...SLC...VEF...

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

LAT...LON   37881299 37591185 36251226 34511327 34421469 
            35121565 35901618 36961632 37751455