MESOSCALE PRECIPITATION DISCUSSION 0432
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
834 PM EDT WED JUL 11 2018

AREAS AFFECTED...SRN/CTRL ARIZONA

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

VALID 120033Z - 120430Z

SUMMARY...SCATTERED THUNDERSTORMS WILL LINGER INTO AT LEAST THE
EARLY EVENING IN PORTIONS OF ARIZONA. THESE STORMS MAY FOCUS IN A
PORTION OF CENTRAL AND WEST-CENTRAL ARIZONA NEAR THE I-10
CORRIDOR. SLOW STORM MOTIONS AND MERGING STORMS MAY ALLOW FOR
LOCALLY HEAVY RAINFALL...RAIN RATES AROUND 2 IN/HR...AND FLASH
FLOODING.

DISCUSSION...AS OF 00Z...SEVERAL BANDS OF CONVECTION WERE
APPROACHING A REGION OF WEST-CENTRAL ARIZONA RELATIVELY
UNDISTURBED BY THUNDERSTORMS YET TODAY. RAP ANALYSIS SHOWED A
MAXIMUM IN MUCAPE VALUES IN THIS SAME REGION...OVER 2000 J/KG IN
SOME PLACES...AND RADAR TRENDS SHOWED THAT SOME STORM MERGERS AND
OUTFLOW BOUNDARY COLLISIONS WERE LIKELY TO TAKE PLACE OVER THE
NEXT SEVERAL HOURS. THE INCREASING CONCENTRATION OF STORMS AND
LIKELIHOOD OF COLLIDING BOUNDARIES IN THE PRESENCE OF A VERY
UNSTABLE AND MOIST (PWATS APPROACHING 2 INCHES AND ABOVE THE 99TH
PERCENTILE IN PORTIONS OF THE AREA) SUGGESTS THAT LOCALLY HEAVY
RAINFALL AND FLASH FLOODING WILL BECOME A GREATER THREAT. RAP
ANALYSIS ALSO SHOWED A SURFACE LOW IN SOUTHWEST ARIZONA...A
DISTINCT TROUGH EXTENDING EAST TOWARD THE PHOENIX METRO AREA...AND
A LOCAL HIGH PRESSURE OVER THE MOGOLLON RIM REGION. THIS MAY ACT
TO ENHANCE CONVERGENCE IN THE VICINITY OF THE I-10 CORRIDOR...AND
THIS MAY FURTHER ENHANCE CONVECTIVE COVERAGE. RAIN RATES OF 2
IN/HR WILL BE POSSIBLE GIVEN THE SLOW STORM MOTIONS AND MERGERS
INTO MEANDERING CONVECTIVE CLUSTERS...AND THIS COULD LEAD TO FLASH
FLOODING... PARTICULARLY IF ALIGNED WITH ANY URBAN AREAS.

CONVECTIVE TRENDS BEYOND 03-04Z ARE LESS CERTAIN. CONVECTIVE
INSTABILITY MAY BE EXHAUSTED IN THE NORTHERN PORTION OF THE
OUTLINED AREA...BUT THE REGION JUST TO THE SOUTH SHOULD REMAIN
SOMEWHAT UNSTABLE. ANY THUNDERSTORM OUTFLOW FROM THE NORTH COULD
TRIGGER ADDITIONAL STORMS IN SOUTHERN ARIZONA. THIS WILL NEED TO
BE MONITORED THIS EVENING...AND COULD LEAD TO A CONTINUING THREAT
OVERNIGHT.

LAMERS

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

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

LAT...LON   34981394 34971192 34171055 32880981 31671043
            31321177 31771326 32641478 34051471