MESOSCALE PRECIPITATION DISCUSSION 0400
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
539 PM EDT THU JUN 30 2016
 
AREAS AFFECTED...SOUTHEAST NV...SOUTHWEST UT...WESTERN
AZ...SOUTHEAST CA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 302138Z - 010200Z
 
SUMMARY...SLOW-MOVING THUNDERSTORMS TO EXPAND IN COVERAGE AND
INTENSITY OVER THE NEXT COUPLE OF HOURS. FLASH FLOODING WILL BE
LIKELY IN THE VICINITY OF DRY WASHES AND ARROYOS AND ALSO NEAR
AREAS OF HIGHER TERRAIN GIVEN INTENSE RAINFALL RATES OF OVER 1.5
INCHES/HR.

DISCUSSION...AFTERNOON VISIBLE SATELLITE IMAGERY SHOWS AN
EXPANSION OF CU/TCU OVER SOUTHEAST NV DOWN INTO WESTERN AZ AND
PARTS OF SOUTHEAST CA WHERE THE AIRMASS IS VERY UNSTABLE. MLCAPE
VALUES OF 2500 TO 3000 J/KG ARE NOTED AND THESE VALUES HAVE BEEN
TENDING TO INCREASE OVER THE LAST COUPLE OF HOURS WITH ADDITIONAL
DIABATIC HEATING TAKING PLACE AND ALSO WITH AN UPTICK IN COLUMN
MOISTURE AS SUGGESTED BY GPS-DERIVED AND GOES-SOUNDER DATA. PWATS
ARE CONCENTRATED BETWEEN 1.5 TO 1.75 INCHES FROM FAR SOUTHERN NV
DOWN THROUGH FAR SOUTHEAST CA.

THE LATEST WV IMAGERY SHOWS A VORT CENTER OVER SOUTH-CENTRAL NV
THAT IS CONNECTED TO THE SOUTHWEST FLANK OF A SHORTWAVE TROUGH
EXITING THROUGH CENTRAL UT. THE HIRES GUIDANCE LED BY THE HRRR
INDICATES AN EXPANSION OF CONVECTION OVER THE NEXT COUPLE OF HOURS
WITH VERY SLOW CELL MOTION EXPECTED AND INTENSE RAINFALL RATES
THAT MAY EXCEED 1.5 INCHES/HR. ALREADY THERE HAVE BEEN SOME VERY
LOCALIZED BUT INTENSE THUNDERSTORMS TO THE NORTHWEST OF LAS VEGAS
AND SOME EXPANSION/ORGANIZATION OF THIS ACTIVITY IS EXPECTED OVER
THE NEXT COUPLE OF HOURS GIVEN THE LEVEL OF DEEPER
MOISTURE/INSTABILITY THAT IS IN PLACE.

THE MAIN FLASH FLOOD CONCERN WILL BE FOR AREA DRY WASHES AND
ARROYOS WHERE THESE TYPES OF RAINFALL RATES TYPICALLY LEAD TO
ENHANCED SHORT-TERM RUNOFF AND FLASH FLOODING CONCERNS.
HOWEVER...AREAS ADJACENT TO SOME OF THE HIGHER TERRAIN OF
NORTHWEST AZ AND SOUTHWEST UT WILL ALSO NEED TO BE MONITORED GIVEN
THE POTENTIAL FOR ENHANCED CHANNELING OF RUNOFF WATER.

ORRISON

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

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

LAT...LON   37941316 37571263 36541261 34851319 33281406 
            32781484 33031547 33481569 34611575 35971550 
            36851516 37761459