MESOSCALE PRECIPITATION DISCUSSION 0506
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
408 PM EDT TUE JUL 18 2017

AREAS AFFECTED...SOUTHEAST NV...SOUTHERN UT...AZ...WESTERN NM

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

VALID 182005Z - 190205Z

SUMMARY...SHOWERS AND THUNDERSTORMS WITH INTENSE RAINFALL RATES
WILL CONTINUE TO EXPAND IN COVERAGE THROUGH THE LATE AFTERNOON AND
EVENING HOURS. SOME POCKETS OF FLASH FLOODING ARE LIKELY.

DISCUSSION...MID-AFTERNOON EXPERIMENTAL GOES-16 10.3 MICRON/IR
IMAGERY IS SHOWING A GRADUAL EXPANSION OF COOLING CONVECTIVE TOPS
OVER WESTERN NM AND EXTENDING WEST ACROSS CENTRAL AND NORTHWEST AZ
INCLUDING THE MOGOLLON RIM. DEVELOPMENT IS ALSO NOTED NOW ACROSS
AREAS OF SOUTHERN UT. STRONG DIURNAL HEATING AND A VERY MOIST
COLUMN ASSOCIATED WITH THE MONSOON PATTERN IS WORKING IN TANDEM
WITH A WEAK MID LEVEL TROUGH AND LOCALIZED OROGRAPHICS/UPSLOPE
FLOW TO ALLOW CONVECTION TO INITIATE AND EXPAND IN COVERAGE.

THE HIRES MODELS ARE ALREADY GENERALLY APPEARING TO BE TOO SLOW TO
INITIATE CONVECTION BASED ON THE LATEST SATELLITE AND RADAR
TRENDS...BUT THEY SUGGEST INTENSE RAINFALL RATES WITH THE
CONVECTION OVER TIME AND WITH RELATIVELY SLOW CELL MOTION OFF TO
THE WEST GIVEN THE FAIRLY WEAK LOW AND MID LEVEL WIND FIELDS OUT
OF THE EAST.

MORNING RAOB DATA FROM PHX/TUS BOTH INDICATED ANOMALOUSLY HIGH
PWATS OF 1.8 TO 1.9 INCHES...AND THE LATEST CIRA-LPW PRODUCT
THROUGH 18Z CONTINUES TO SHOW AN ENVIRONMENT CONDUCIVE FOR HIGHLY
EFFICIENT RAINFALL PROCESSES THAT IN CONJUNCTION WITH MLCAPE
VALUES OF 1500 TO 2000 J/KG WILL LIKELY PRODUCE RAINFALL RATES AS
HIGH AS 2.5 INCHES/HR AS CONVECTION CONTINUES TO DEVELOP AND
BECOME LOOSELY ORGANIZED THROUGH THE AFTERNOON AND EVENING HOURS.
THE GENERAL MOTION SHOULD BE OFF TO THE WEST

IN ADDITION TO AREAS OF WESTERN NM AND AZ...EXPECT THUNDERSTORMS
TO GRADUALLY BECOME MORE FOCUSED/CONCENTRATED OVER SOUTHERN UT AND
IN TIME OVER PARTS OF SOUTHEAST NV GOING CLOSER TO THE EVENING
TIME-FRAME.

THE 12Z ARW/NMMB SOLUTIONS SUPPORT AS MUCH AS MUCH AS 3 TO 4
INCHES OF RAIN WITHIN SOME OF THE STRONGER CONVECTIVE CORES...AND
THIS WILL LIKELY RESULT IN FLASH FLOODING FOR AREA DRY
WASHES/ARROYOS AND OTHER MORE SENSITIVE AREAS INVOLVING HIGHER
TERRAIN AND ADJACENT CANYONS WHERE RUNOFF CAN BE GREATLY ENHANCED.
WILL CONTINUE TO MONITOR.

ORRISON

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

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

LAT...LON   38161214 37201074 36060926 35140797 33650730
            32720769 32380820 32190910 32351069 33181183
            33671253 34461391 35151487 36071538 37261535
            38091442