MESOSCALE PRECIPITATION DISCUSSION 0427
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
632 PM EDT MON JUL 09 2018

AREAS AFFECTED...SRN AND CTRL ARIZONA

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

VALID 092231Z - 100430Z

SUMMARY...THUNDERSTORMS WERE BECOMING MORE NUMEROUS ACROSS
SOUTHERN AND CENTRAL ARIZONA THIS AFTERNOON...AND MAY BECOME
INCREASINGLY CONCENTRATED IN SOUTHWEST ARIZONA THIS EVENING. RAIN
RATES OF 1-2 IN/HR HAVE ALREADY BEEN OBSERVED AND ARE LIKELY TO
CONTINUE INTO THE EVENING. THIS MAY LEAD TO AREAS OF FLASH
FLOODING.

DISCUSSION...KIWA AND KEMX RADARS SHOW TWO PRIMARY BANDS OF
CONVECTION AS OF 2230Z. THE FIRST WAS ADVANCING SOUTHWEST OFF THE
MOGOLLON RIM IN CENTRAL ARIZONA...AND THE SECOND WAS ORIENTED MORE
NORTH-SOUTH... ADVANCING WEST AHEAD OF AN UPPER LEVEL LOW. THE
COMBINATION OF THESE STORM MOTIONS WOULD TEND TO FAVOR A
CONFLUENCE OF CONVECTION OVER SOUTHWEST ARIZONA LATE THIS
AFTERNOON AND EVENING... PARTICULARLY OVER MARICOPA... WESTERN
PINAL... AND NORTHWEST PIMA COUNTIES. THIS REGION OF SRN ARIZONA
ALSO HAD THE HIGHEST PRECIPITABLE WATER VALUES... WITH CIRA
BLENDED TPW BETWEEN 1.5 AND 2.0 INCHES AND A COUPLE GPS-PW
OBSERVATIONS NEAR THE INTERNATIONAL BORDER IN THAT RANGE. SPC
MESOANALYSIS FROM THE RAP MODEL SHOWS MORE STABLE CONDITIONS WITH
STRONG CINH IN THE VICINITY OF THE COLORADO RIVER AT THE MOMENT
(ALSO IMPLIED BY THE LACK OF CLOUDS ON VISIBLE SATELLITE)... BUT
MODERATE TO STRONG INSTABILITY AROUND 1500 J/KG MLCAPE IN AN AREA
OF SW AZ CENTERED ON MARICOPA COUNTY. THEREFORE... THE COMBINATION
OF FAIRLY STRONG INSTABILITY AND HIGH PWS SHOULD SUPPORT HEAVY
RAIN RATES APPROACHING 2 IN/HR AT TIMES... WHICH WOULD FAVOR THE
THREAT OF LOCALIZED FLASH FLOODING.

GIVEN THE STILL SCATTERED NATURE OF THE CONVECTION... FLASH
FLOODING SHOULD BE SOMEWHAT LOCALIZED IF IT OCCURS. ALTHOUGH THE
CONFIGURATION OF THE SYNOPTIC PATTERN AND WIND FIELDS DO NOT FAVOR
TRAINING CONVECTION... RAIN RATES SHOULD BE SUFFICIENT FOR FLASH
FLOODING. SEVERAL ARIZONA FLOOD WARNING SYSTEM GAGES HAVE RECENTLY
REPORTED AROUND 0.5 INCHES OF RAIN IN AS LITTLE AS 15-30 MINUTES.
RAIN RATES OF THIS MAGNITUDE WOULD HAVE THE POTENTIAL TO CAUSE
FLOODING ISSUES REGARDLESS OF TRAINING... PARTICULARLY IN URBAN
AREAS.

IN THE NEXT COUPLE HOURS (THROUGH 01Z)... THE GREATEST CHANCE OF
FLASH FLOODING SHOULD GENERALLY BE IN THE ARIZONA SUN CORRIDOR
FROM PHOENIX TO TUCSON AND ADJACENT AREAS... AND BEYOND THAT
BUILDING SOUTHWEST INTO PORTIONS OF THE SONORAN DESERT.

LAMERS

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

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

LAT...LON   35011316 34541186 34171076 33111026 31871068
            31411182 31741328 32181436 33261446 34411440