MESOSCALE PRECIPITATION DISCUSSION 0623
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
857 PM EDT FRI AUG 04 2017

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

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 050055Z - 050615Z

SUMMARY...CLUSTERS OF HEAVY SHOWERS AND THUNDERSTORMS WILL
CONTINUE INTO THE EVENING HOURS AND RESULT IN SOME ADDITIONAL
FLASH FLOODING CONCERNS.

DISCUSSION...THE LATE-DAY GOES-16 10.3 MICRON/IR IMAGERY SHOWS
SCATTERED CLUSTERS OF COLD-TOPPED SHOWERS AND THUNDERSTORMS
CONTINUING ACROSS MUCH OF THE SOUTHWEST GIVEN THE INTERACTION OF
AN ELONGATED MID LEVEL TROUGH WITH ROBUST BOUNDARY LAYER
HEATING/INSTABILITY AND MONSOONAL MOISTURE. MUCH OF THE MID LEVEL
ENERGY IS STRETCHED FROM CENTRAL CA EAST ACROSS SOUTHERN
NV...SOUTHERN UT AND DOWN INTO NORTHERN AZ. EMBEDDED WITHIN THIS
AXIS OF TROUGHING HAS BEEN A COUPLE OF WELL-DEFINED MCVS AS
WELL...ESPECIALLY WITH THE ONE OVER SOUTHERN NV...WHICH HAVE BEEN
YIELDING SOME FOCUSED AREAS OF CONVECTION AND VERY HEAVY RAINFALL.

OVER THE NEXT FEW HOURS...THE CONVECTIVE THREAT WILL CONTINUE AND
ESPECIALLY OVER AREAS NEAR THE SOUTHERN SIERRA-NEVADA AND EAST OUT
ACROSS THE SOUTHERN PORTIONS OF BOTH NV AND UT AS FAVORABLE MID
LEVEL DEFORMATION/FORCING COUPLED WITH MULTIPLE WELL-DEFINED
SURFACE MESOSCALE/OUTFLOW BOUNDARIES INTERACT WITH A STILL
FAVORABLY MOIST/UNSTABLE BOUNDARY LAYER FOR CONVECTION. IN
FACT...THE LATEST HRRR/HRRRX GUIDANCE SUGGESTS SOME POTENTIAL FOR
GREATER CONVECTIVE ORGANIZATION...AND AN ADDITIONAL 2 TO 3 INCHES
OF RAIN POSSIBLE THROUGH AT LEAST 06Z. FLASH FLOODING WILL
DEFINITELY REMAIN A CONCERN AS A RESULT FOR THESE AREAS.

FARTHER SOUTH OVER NORTHERN AZ...CONDITIONS HERE WILL STILL FAVOR
SOME ADDITIONAL CONVECTION AND ESPECIALLY NEAR THE MOGOLLON RIM
AREA....BUT THE LATEST GOES-15 WV IMAGERY IS SHOWING A SIGNIFICANT
INTRUSION OF MID LEVEL DRY AIR WHICH WILL REDUCE THE RAINFALL
RATES. NEVERTHELESS...SOME ADDITIONAL AMOUNTS OF 1 TO 2 INCHES
WILL BE POSSIBLE ALONG WITH SOME LOCALIZED RUNOFF CONCERNS BEFORE
CONVECTION WEAKENS LATER IN THE EVENING.

ORRISON

ATTN...WFO...FGZ...GJT...HNX...LKN...REV...SLC...VEF...

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

LAT...LON   39031314 38671195 37661038 36200940 34510957
            34151046 34211153 34781221 35321267 35871353
            36021444 35861586 35891674 36181762 36781882
            37511916 38001889 38511782 38831662 39001501