MESOSCALE PRECIPITATION DISCUSSION 0676
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1035 PM EDT SAT AUG 12 2017

AREAS AFFECTED...CENTRAL/SOUTHERN AZ...SOUTHWEST NM

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

VALID 130230Z - 130730Z

SUMMARY...VERY HEAVY SHOWERS AND THUNDERSTORMS WILL CONTINUE OVER
THROUGH THE EVENING HOURS WITH ADDITIONAL FLASH FLOODING LIKELY.

DISCUSSION...THE LATEST RADAR IMAGERY SHOWS A FAIRLY WELL
ORGANIZED AXIS OF SHOWERS AND THUNDERSTORMS MOVING GRADUALLY SOUTH
THROUGH CENTRAL AZ WHICH IS CONTINUING TO PRODUCE VERY HEAVY
RAINFALL. SOMEWHAT MORE DISORGANIZED CONVECTION MEANWHILE IS SEEN
BACK OVER AREAS OF SOUTHWEST NM.

PWATS ACROSS THE REGION ARE RATHER HIGH...WITH GOES-15 SOUNDER
DATA AND 00Z RAOB DATA SUGGESTING VALUES OF OF 1.5 TO 1.75 INCHES.
THIS HAS BEEN SUPPORTING ENHANCED RAINFALL RATES...AND ESPECIALLY
WITH A RELATIVELY ENHANCED CONCENTRATION OF MOISTURE IN THE
500/700 MB LAYER AS PER CIRA-LPW DATA. IN FACT...RAINFALL TOTALS
OVER PORTIONS OF THE MOGOLLON RIM LATE THIS AFTERNOON AND EARLY
EVENING HAVE BEEN OVER 2.5 INCHES/HR...WITH AS MUCH AS 3 TO 4
INCHES OF RAIN IN JUST A 2 HOUR PERIOD. A COUPLE OF CELL-MERGERS
AND GENERALLY SLOW CELL MOTION HAVE CONTRIBUTED TO THESE HEAVIER
AMOUNTS.

THE CONVECTION OVER CENTRAL AZ HAS BECOME SOMEWHAT OUTFLOW
DOMINANT AT THIS POINT AND IS EXPECTED TO CONTINUE DROPPING SOUTH
THROUGH SOUTHERN AZ THROUGH THE REMAINDER OF THE EVENING HOURS
CONSIDERING IT WILL BE ENCOUNTERING A MODERATELY UNSTABLE AIRMASS
WITH MLCAPE VALUES OF 1500 TO 2000 J/KG...AND WILL BE EMBEDDED
WITHIN A DIFFLUENT UPPER AIR PATTERN AS SEEN IN THE LATEST GOES-WV
IMAGERY. RAINFALL RATES WILL REMAIN RATHER HIGH GIVEN THE
RELATIVELY HIGH PWAT ENVIRONMENT AND DEEPER AND COLDER CONVECTIVE
TOPS.

THE HIRES MODEL GUIDANCE HAS BEEN BADLY UNDERDONE WITH THE
RAINFALL FORECAST ACROSS THE SOUTHWEST THIS AFTERNOON AND GIVEN
THE LEVEL OF CURRENT CONVECTIVE ORGANIZATION...THE MODELS APPEAR
TO STILL BE WAY TOO DRY. ONLY THE HRRRX HAS SOME SEMBLANCE OF
HANDLING THE CURRENT CONVECTION CORRECTLY.

EXPECT AS MUCH AS 3 TO 4 INCHES OF RAIN LOCALLY THROUGH THE
EVENING HOURS AS CONVECTION CONTINUES TO ADVANCE SOUTH TOWARD
SOUTHERN AZ...AND TENDS TO PERSIST TO A DEGREE AS WELL OVER
SOUTHWEST NM. ADDITIONAL FLASH FLOODING IS LIKELY...WITH
PARTICULAR FOCUS OVER THE DRY WASHES/ARROYOS AND ADJACENT AREAS OF
STEEPER TERRAIN.

ORRISON

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

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

LAT...LON   35081259 35081201 34381048 34340888 34580785
            34220709 33530688 32700687 31880724 31240836
            31320961 31331052 31451142 31781193 32351272
            33021341 33741389 34501399 34991346