MESOSCALE PRECIPITATION DISCUSSION 0437
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
130 PM EDT THU JUL 12 2018

AREAS AFFECTED...SOUTHEAST CA...SOUTHERN NV...NORTHWEST & NORTH
CENTRAL AZ...

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 121730Z - 122200Z

SUMMARY...SCATTERED THUNDERSTORMS WITH AMPLE MOISTURE CAPABLE OF
PRODUCING 1-2" IN A HOUR LEADING TO HIGHLY LOCALIZED FLASH
FLOODING THROUGHH THE AFTERNOON HOURS.

DISCUSSION...GOES-16 1 MINUTE VISIBLE IMAGERY DEPICTS CONVECTIVE
INITIATION ALONG THE LOCAL TOPOGRAPHICAL RANGES ACROSS NW AZ /S NV
INTO SE CA.  AMPLE EARLY MORNING SUN HAS ALREADY INCREASED SURFACE
TEMPS INTO THE 80S-90S TO BE SUFFICIENT TO BREAK THE LIMITED CAP. 
MOISTURE HAS ALSO FUNNELED UP THROUGH THE COLORADO RIVER VALLEY
WITH VEF 12Z TPWS OVER 1.5" AND NEARING 2" FURTHER SOUTH TOWARD
THE WESTERN SONORAN DESERT OF SW AZ.  MID-LEVEL CLOUD COVER HAS
REDUCED INSOLATION NEAR THE NV/AZ/UT BOARDER THROUG THE GRAND
CANYON REGION TOWARD CENTRAL AZ/MOGOLLON RIM ASSOCIATED WITH THE
MCV FROM LAST EVENING'S COMPLEX.  STILL WHERE THERE ARE
BREAKS...SOME TCU AND CBS ARE STARTING TO SPROUT AS WELL.

THE UPPER LEVEL PATTERN SHOWS THE SHEARING UPPER LOW OFF THE NW
PORTION OF THE CALIFORNIA BIGHT EXTENDING THE TROF BACK THROUGH
THE AREA OF CONCERN TO THE MCV IN NEAR FLG...PROVIDING SOME
MID-LEVEL STEEPER LAPSE RATES BUT MORE IMPORTANTLY LIMITED FLOW
ABOUT 5-8KTS MAX FOR CELL MOTIONS).  RAP SUGGESTS THE
CLEAR/UNCAPPED AREAS SUPPORT SBCAPES TO 2000-3000 J/KG ACROSS S NV
INTO NW AZ TO FUEL STRONG UPDRAFTS AND ABLE TO CONVERT THE LOCAL
MOISTURE IN THE 1.5" TPW RANGE INTO RAIN TOTALS OF 1-2" TYPICALLY
FALLING IN LESS THAN AN HOUR BEFORE DISSIPATING. 
EVENTUALLY...OUTFLOW BOUNDARIES FROM THE INITIAL CELLS SHOULD SPUR
NEW DEVELOPMENT DOWNSTREAM WITH SOME HI-RES CAMS SUGGESTING A
GREATER THREAT FURTHER NORTH IN CENTRAL NV AND POSSIBLY LAS VEGAS
PROPER INCREASING THE FLASH FLOOD RISK TODAY. 

FURTHER WEST INTO NE AZ...MORE TIME IS NEEDED TO BURN OFF CLOUDS
AND INCREASE INSOLATION DELAYING CONVECTIVE DEVELOPMENT AND FLASH
FLOOD THREAT.  FURTHER SOUTH ACROSS FAR SE CA/SW AZ...BETTER
MOISTURE/INSTABILITY IS AVAILABLE BUT STRONGER CAPPING AND LIMITED
LOW LEVEL CONVERGENCE IS LIKELY TO LIMIT DEVELOPMENT UNTIL MUCH
LATER IF AT ALL.  STILL WILL CONTINUE TO MONITOR BOTH AREAS FOR
NEW DEVELOPMENT POTENTIAL.

GALLINA 

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

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

LAT...LON   37491632 37341556 36941464 36811439 36851364
            36781321 36541287 36051202 35651135 35111092
            34091094 34221204 34391379 34501488 34541520
            34731618 35261684 35811727 36411739 36681726
            37221678