MESOSCALE PRECIPITATION DISCUSSION 0562
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
152 PM EDT TUE JUL 25 2017

AREAS AFFECTED...EXTREME EASTERN CA...FAR SOUTHEAST
NV...CENTRAL/NORTHERN AZ...SOUTHERN UT

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

VALID 251750Z - 252350Z

SUMMARY...THE THREAT FOR HEAVY RAIN AND FLASH FLOODING CONTINUES
AS SHOWERS AND THUNDERSTORMS ARE EXPECTED TO PERSIST.

DISCUSSION...THE LATEST EXPERIMENTAL GOES-16 1-MINUTE 10.3
MICRON/IR AND 0.64 MICRON/VIS DATA SHOWS A GRADUAL SOUTHEASTWARD
SETTLING OF A CONCENTRATED AND PERSISTENT AREA OF COLD-TOPPED
CONVECTION OVER FAR SOUTHEAST NV AND NORTHWEST AZ...WITH THE
CONVECTION CONTINUING TO INVOLVE MORE AREAL COVERAGE OVER
NORTHWEST AZ AND ALSO DEVELOPING IN CLOSE PROXIMITY TO PARTS OF
FAR EASTERN CA.

THERE IS REALLY NO CHANGE TO THE PREVIOUS SHORT-TERM FORECAST
RATIONALE. THE ENHANCED MONSOONAL SET-UP WILL CONTINUE TO FOSTER
HEAVY RAINFALL AS ADDITIONAL SHOWERS AND THUNDERSTORMS DEVELOP.
THE CONVECTION IS
FOCUSING GENERALLY ALONG AND SOUTH OF A 700 MB LOW AND ASSOCIATED
TROUGH AXIS WHICH IS ENHANCING CONVERGENT FLOW WITHIN A MODESTLY
UNSTABLE AND VERY MOIST COLUMN. THERE IS FURTHER AID ALSO IN THE
FORM OF DIVERGENT FLOW ALOFT AROUND THE EASTERN FLANK OF AN UPPER
LOW/TROUGH OVER CENTRAL/NORTHERN CA.

PWATS THIS MORNING REMAIN HIGHLY ANOMALOUS ACROSS THE REGION...AS
EVIDENCED BY THE 12Z LAS VEGAS RAOB WHICH REPORTED A 1.92 INCH
PWAT. THIS IS AT OR NEAR AN ALL-TIME RECORD. GENERALLY ACROSS THE
REGION THE PWATS HAVE BEEN 1.7 TO 2.0 INCHES WHICH ARE AT LEAST IN
THE 95TH TO 99TH PERCENTILE RELATIVE TO CLIMATOLOGY. THE 15Z
CIRA-LPW DATA PLOT CONFIRMS THE PERSISTENCE OF A DEEP COLUMN OF
TROPICAL MOISTURE...WITH SOME MID TO HIGH LEVEL ORIGINS EXTENDING
WELL SOUTH OVER MEXICO AND OVER THE EASTERN TROPICAL PACIFIC BASIN.

THE SW/NE ORIENTED LOW TO MID LEVEL TROUGH AXIS AND LOW CENTER IS
FORECAST TO DRIFT EAST THROUGH THE AFTERNOON...AND THIS COUPLED
WITH DIURNAL HEATING/INSTABILITY AND OROGRAPHICS WILL HELP FOCUS
CONVECTION A BIT FARTHER SOUTH AND EAST WITH TIME. THIS WILL
INCLUDE AREAS OVER AND NEAR THE MOGOLLON RIM.

THE HEAVIEST RAINFALL AMOUNTS WILL LIKELY REMAIN FOCUSED OVER
AREAS OF FAR SOUTHEAST NV...NORTHWEST AZ AND PERHAPS A VERY SMALL
PORTION OF FAR EASTERN CA. RAINFALL AMOUNTS HERE OF AS MUCH AS 2
TO 4 INCHES WILL BE POSSIBLE OVER THE NEXT 6 HOURS. ELSEWHERE
ACROSS THE MPD THREAT AREA...INCLUDING THE REMAINDER OF
CENTRAL/NORTHERN AZ AND UP ACROSS SOUTHERN UT...THE CONVECTION
WILL BE MORE SCATTERED IN NATURE...BUT STILL CAPABLE OF PRODUCING
SOME 2 TO 3 INCH AMOUNTS. THESE AMOUNTS WILL CONTINUE TO FAVOR
FLASH FLOODING CONCERNS...AND SOME OF IT MAY BE SIGNIFICANT GIVEN
CHANNELING OF WATER OFF HIGHER TERRAIN AND THROUGH AREA CANYONS.
ARROYOS AND DRY WASHES WILL ALSO BE PARTICULARLY PRONE. WILL
CONTINUE TO MONITOR.

ORRISON

ATTN...WFO...FGZ...GJT...PSR...SLC...VEF...

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

LAT...LON   39441012 38840919 38030909 37550930 36401022
            35761023 34671007 33871046 33721120 33981199
            34281280 34071360 34001441 34341524 35021537
            35541530 36271458 37711308 38731198