MESOSCALE PRECIPITATION DISCUSSION 0485
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
929 PM EDT THU JUL 19 2018

AREAS AFFECTED...PORTIONS OF AZ, UT, & NV

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

VALID 200128Z - 200508Z

SUMMARY...CONVECTION HAS MATURED ACROSS THE REGION DURING THE PAST
FEW HOURS.  THE AVAILABLE MOISTURE AND INSTABILITY SHOULD ALLOW
FOR HOURLY RAIN TOTALS TO 2" LOCALLY THROUGH 05Z.

DISCUSSION...THE DESERT SOUTHWEST IS WITHIN A CONFLUENT FLOW
REGIME/MOISTURE CHANNEL BETWEEN AN UPPER LOW WEST OF BAJA
CALIFORNIA AND MID-LEVEL RIDGING ACROSS TX.  BECAUSE OF THIS,
PRECIPITABLE WATER VALUES REMAIN ENHANCED, WITH GPS DATA SHOWING
MAXIMA NEAR 2" NEAR YUMA AZ AND SOUNDINGS SHOWING VALUES CLOSER TO
1.5" NEAR LAS VEGAS.  THIS HAS LED TO ENHANCED MONSOON CONDITIONS
THIS AFTERNOON INTO EARLY THIS EVENING.  IT APPEARS CONVECTION
FORMED ALONG A DISTENDED 700 HPA TROUGH AXIS SHOWING UP IN VAD
WIND PROFILE DATA ACROSS SOUTHERN NV, NORTHERN AZ, AND NEAR THE NM
PORTION OF THE CONTINENTAL DIVIDE BEFORE OUTFLOW BOUNDARIES AND
THE GENERAL INSTABILITY PATTERN FORCED A PREFERRED WESTWARD
PROPAGATION NEAR AND TO THE SOUTH OF THE 500 HPA RIDGE AXIS
EXTENDING FROM CENTRAL NV INTO THE FOUR CORNERS.

THE AVAILABLE MOISTURE AND INSTABILITY SHOULD SUPPORT ACTIVE
CONVECTION THROUGH ROUGHLY 05Z, BEFORE CIN FULLY SETS IN.  UNTIL
THEN, HOURLY RAIN TOTALS TO 2" ARE POSSIBLE.  THE MESOSCALE
GUIDANCE SHOWS LOCAL AMOUNTS OF 3" DURING THE NEXT SEVERAL HOURS,
WHICH LOOKS REALISTIC.  THIS RAINFALL WOULD BE MOST PROBLEMATIC IN
ARROYOS/WASHES, BURN SCARS, AND URBAN AREAS.

ROTH

ATTN...WFO...FGZ...HNX...LKN...PSR...REV...SLC...TWC...VEF...

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

LAT...LON   39831453 39481351 37981293 37231120 34900908
            32961001 33631196 34761412 35561581 36971864
            39071803