MESOSCALE PRECIPITATION DISCUSSION 0506
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
530 PM EDT TUE SEP 22 2015
 
AREAS AFFECTED...PORTIONS OF AZ 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 222230Z - 230230Z
 
SUMMARY...CONVECTION DEVELOPING ACROSS THE HIGHER TERRAIN IN AZ
TRANSITIONS FROM DYNAMICALLY DRIVEN TO MAINLY DIURNALLY DRIVEN
INTO THE LATE AFTERNOON HOURS. THE CONVECTION TAPS HIGH MOISTURE
CONTENT AIR...RESULTING IN LOCAL FLASH FLOODING DUE TO CELL
TRAINING.

DISCUSSION..A MID LEVEL CIRCULATION OVER NORTHEAST AZ WILL
CONTINUE TRACKING NORTHEAST THROUGH THE LATE AFTERNOON HOURS. AS
THE CIRCULATION EXITS...THE DYNAMICALLY DRIVEN CONVECTION STARTS
TO WANE...AND THE REMAINING CONVECTION BECOMES MOSTLY DIURNALLY
DRIVEN. A LOW TO MID LEVEL SOUTHWEST FLOW FEEDS PRECIPITABLE WATER
VALUES BETWEEN TWO AND THREE STANDARD DEVIATIONS ABOVE NORMAL
ACROSS MUCH OF NORTHERN AND WESTERN AZ.

AS THE CONVECTION BECOMES MORE DIURNALLY DRIVEN...IT SHOULD BE
PRIMARILY ROOTED IN THE TERRAIN...WITH THE BEST MOISTURE FEED
ACROSS SOUTHWEST AZ. THE EXTENT OF THE COVERAGE SHOULD PEAK BEFORE
23/00Z...AND START WANING AFTER 23/02Z. BEFORE THAT
TIME...CONVECTIVE CELLS TAP THE DEEP MOISTURE TO PRODUCE LOCAL
RAINFALL AMOUNTS NEAR 1.50 INCHES. THESE AMOUNTS ARE STRONGLY
SUPPORTED BY THE LATEST HRRR/12Z WRF ARW...WITH THE HIGHEST
AMOUNTS OVER NORTHWEST AZ.

THESE RAINFALL AMOUNTS ARE ABOVE THE ONE AND THREE HOUR FLASH
FLOOD GUIDANCE VALUES ACROSS CENTRAL AND WESTERN AZ. FLASH
FLOODING IS POSSIBLE...ESPECIALLY WHERE CELLS TRAIN. OVERALL...THE
THREAT SHOULD REMAIN SCATTERED...AS THE BEST MID LEVEL FORCING
EXITS THE AREA. THE THREAT FOR FLASH FLOODING SHOULD DROP OFF
AFTER 23/02Z.

HAYES

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

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

LAT...LON   36751099 35801021 34230949 32910952 32090984 
            31831038 31781116 31651157 31531210 31731271 
            32051372 32461435 32851434 33101410 33471341 
            34121285 34471310 35681344 36541314