MESOSCALE PRECIPITATION DISCUSSION 0449
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
205 PM EDT SAT JUL 14 2018

AREAS AFFECTED...SOUTHERN UT...AZ...WEST-CENTRAL AND SOUTHERN NM

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 141805Z - 142305Z

SUMMARY...SLOW-MOVING SHOWERS AND THUNDERSTORMS TO BECOME MORE
NUMEROUS GOING THROUGH THE AFTERNOON HOURS. HEAVY RAINFALL RATES
ARE LIKELY TO RESULT IN SOME FLASH FLOODING.

DISCUSSION...THE LATEST GOES-16 VISIBLE IMAGERY HAS BEEN SHOWING A
GRADUAL EROSION OF SOME OF THE LOW LEVEL CLOUDINESS ACROSS AREAS
OF SOUTHERN UT AND DOWN THROUGH CENTRAL AND SOUTHEAST AZ. THIS IS
ALLOWING FOR SUFFICIENT DIURNAL HEATING FOR AN INCREASE IN
BOUNDARY LAYER INSTABILITY AND EROSION OF LOW LEVEL CINH ACROSS
THE REGION. THE LATEST RAP ANALYSIS SHOWS MLCAPE VALUES OF OVER
1000 J/KG OVER CENTRAL AZ AND IN VICINITY OF A WELL-DEFINED MCV
WHICH IS CENTERED TO A LITTLE SOUTH-SOUTHEAST OF KFLG.
MEANWHILE...THERE HAS BEEN MORE SUNSHINE AND SUBSEQUENT HEATING
FARTHER EAST OVER AREAS OF WEST-CENTRAL TO SOUTHERN NM WHICH IS
SUPPORTING MLCAPE VALUES OF AS MUCH AS 1500 J/KG HERE.

CONVECTION IS ALREADY BEGINNING TO INITIATE OVER THE HIGHER
TERRAIN OF SOUTHERN UT...NORTHERN AZ AND WELL EAST OVER
WEST-CENTRAL TO SOUTHERN NM...AND THIS WILL OCCUR ALSO OVER
CENTRAL AND SOUTHEAST AZ WHERE ADDITIONAL HEATING IN CONJUNCTION
WITH ANOMALOUS MOISTURE AND THE AFOREMENTIONED MCV WILL SUPPORT
CONVECTION INTENSIFYING AND EXPANDING IN COVERAGE OVER THE NEXT
COUPLE OF HOURS. OROGRAPHIC FORCING WILL AGAIN TEND TO FOCUS THE
CONVECTION...AND WITH VERY WEAK FLOW ALOFT...THE CELL MOTIONS WILL
BE VERY SLOW WHICH WILL SET THE STAGE FOR LOCALLY VERY HEAVY
RAINFALL TOTALS.

PWATS ACROSS THE REGION ARE NEAR 1.75 INCHES ACROSS SOUTHERN AZ
AND AREAWIDE THE PWAT ANOMALIES ARE 2 TO 3 SIGMAS ABOVE
NORMAL...WITH THE HIGHEST ANOMALIES OVER SOUTHERN UT. EXPECT
HIGHLY EFFICIENT RAINFALL PROCESSES FOR ENHANCED RAINFALL RATES
THAT WILL LOCALLY EXCEED 2 INCHES/HR.

THE HIRES MODEL GUIDANCE FROM 12Z IS IN RATHER GOOD AGREEMENT ON
WIDESPREAD COVERAGE OF SHOWERS AND THUNDERSTORMS GOING THROUGH THE
AFTERNOON HOURS...WITH STORM TOTALS OF AS MUCH AS 2 TO 3 INCHES.
MUCH OF THE CONVECTION TO TEND TO BE OF THE PULSE TYPE...BUT SOME
LOCALLY MORE ORGANIZED MULTI-CELL CONVECTION IS EXPECTED WHERE
CONVECTIVELY INDUCED OUTFLOW BOUNDARIES EVOLVE AND INTERACT WITH
EACH OTHER.

THE CONCERN AGAIN WILL BE FOR INTENSE SHORT-TERM RAINFALL RATES
WHICH WILL LIKELY RESULT IN SOME AREAS OF FLASH FLOODING. MORE
SUSCEPTIBLE AREAS WILL INCLUDE SLOT-CANYONS...DRY WASHES AND BURN
SCARS ALONG WITH AREAS ADJACENT AND DOWNSTREAM FROM THESE
LOCATIONS.

ORRISON

ATTN...WFO...ABQ...EPZ...FGZ...GJT...PSR...SLC...TWC...VEF...

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

LAT...LON   39031211 38961099 38281047 37101052 36140953
            35310777 35000667 34130552 32900547 32450576
            32030642 31820773 31420876 31330997 31881142
            33241201 34081251 34921345 36191388 37761347
            38671277