MESOSCALE PRECIPITATION DISCUSSION 0579
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
424 PM EDT FRI OCT 16 2015
 
AREAS AFFECTED...NORTHERN AND WESTERN AZ 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 162025Z - 170030Z
 
SUMMARY...INCREASING INSTABILITY IN A HIGH MOISTURE CONTENT AIR
MASS WILL FEED CONVECTION THAT PRODUCES A FLASH FLOOD THREAT
THROUGH THE LATE AFTERNOON HOURS.

DISCUSSION...LATEST VISIBLE SATELLITE IMAGES SHOWED INSTABILITY
INCREASING OVER WESTERN AND NORTHERN AZ AS THE CIN IN PLACE IS
EXHAUSTED. MOISTURE AND INSTABILITY ARE BECOMING FOCUSED ON
WESTERN AZ ON THE NOSE OF THE 20 KT 850-700 MB FLOW. LIGHTNING
ACTIVITY HAS SHOWN A SHARP INCREASE IN THE PAST HOUR...SUGGESTING
STRENGTHENING UPDRAFTS IN THE DEVELOPING CONVECTION.  

THE CONVECTION WILL HAVE ACCESS TO DEEP MOISTURE...WITH A SHARP
PRECIPITABLE WATER GRADIENT ALONG AND EAST OF A SURFACE TROUGH
OVER WESTERN AZ. PRECIPITABLE WATER VALUES AS HIGH AS 1.50 INCHES
(WHICH IS ABOUT FOUR STANDARD DEVIATIONS ABOVE THE MEAN) COULD
RESULT IN HIGH RAINFALL RATES IN THE CONVECTION THAT FORMS IN THE
LOW LEVEL CONVERGENCE OVER WESTERN AND NORTHERN AZ. LOCAL 2+ INCH
RAINFALL IS POSSIBLE IN AREAS WHERE CELL TRAINING OCCURS...AS THE
MID LEVEL FLOW SHOULD PRECLUDE FLASH FLOODING FROM SLOW MOVING
CELLS.

MOST OF THE HIGH RESOLUTION GUIDANCE (SUCH AS THE LATEST
HRRR...12Z WRF-ARW/NMMB AND 12Z NSSL WRF) WAS TARGETING SOUTHEAST
CA AND NORTH CENTRAL AZ WITH THE HIGHEST RAINFALL AMOUNTS (NEAR 2
INCHES)...WITH A RELATIVE MINIMUM ACROSS WESTERN AND NORTHWEST AZ. 

THE THREAT FOR FLASH FLOODING SHOULD CONTINUE INTO THE LATE
AFTERNOON HOURS...AS INSTABILITY REMAINS IN PLACE.

HAMRICK/HAYES

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

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

LAT...LON   36691228 34961126 33781124 33761123 32931130 
            32091149 31901203 32431287 33161335 34681415 
            35541416 36661369