MESOSCALE PRECIPITATION DISCUSSION 0442
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
846 PM EDT THU JUL 12 2018

AREAS AFFECTED...ERN CA...SRN NV...SW UT...NW AZ

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

VALID 130045Z - 130545Z

SUMMARY...SCATTERED THUNDERSTORMS SHOULD GRADUALLY DIMINISH INTO
THE EVENING HOURS...BUT LINGERING STORMS WILL MOVE SLOWLY AND
COULD PRODUCE LOCALLY HEAVY RAINFALL. RAIN RATES TO AROUND 2 IN/HR
WILL BE POSSIBLE...WHICH SHOULD CAUSE FLASH FLOODING.

DISCUSSION...GOES-15 IR SATELLITE CONTINUED TO SHOW COLD CLOUD
TOPS FROM THE CENTRAL SIERRAS INTO THE MOJAVE DESERT OF SERN
CALIFORNIA...AND EAST INTO PARTS OF SRN NEVADA AND SWRN UTAH.
THESE COLD CLOUD TOPS WERE GENERALLY NOT SHRINKING IN ANY
APPRECIABLE WAY AS OF 00Z...AND REGIONAL RADARS ALSO SHOWED SLOWLY
DRIFTING CONVECTION SCATTERED ACROSS THE REGION. AS THE EVENING
PROGRESSES AND THE SUN BEGINS TO SET... CONVECTIVE COVERAGE SHOULD
CONTRACT AND IS LIKELY TO BECOME INCREASINGLY FOCUSED AROUND
INSTABILITY MAXIMA. RAP MODEL ANALYSIS PLACED TWO MLCAPE MAXIMA
(OVER 1000 J/KG) IN THE REGION... ONE FROM THE CLARK-LINCOLN (NV)
COUNTY BORDER EAST INTO NRN MOHAVE COUNTY AZ... AND ANOTHER FROM
LAS VEGAS INTO THE MOHAVE VALLEY. THESE INSTABILITY LEVELS SHOULD
BE SUFFICIENT TO MAINTAIN AT LEAST SOME CONVECTION FOR ANOTHER
SEVERAL HOURS. WITH MEAN WINDS 5 KNOTS OR LESS... THE STORMS THAT
DO LINGER INTO THE EVENING SHOULD MOVE VERY SLOWLY AND THUS HAVE
THE POTENTIAL TO PRODUCE LOCALLY VERY HEAVY RAINFALL. PRECIPITABLE
WATER VALUES WERE ABOVE 1.5 INCHES IN THE LOWER ELEVATION PORTIONS
OF THE REGION... THE DESERTS FROM SERN CA INTO SRN NV AND FAR WRN
AZ. AND PWATS WERE AS HIGH AS AN INCH EXTENDING INTO THE CENTRAL
SIERRAS... BASIN AND RANGE OF CENTRAL NEVADA... AND RANGES OF
SOUTHWEST UTAH. THESE ARE ABOVE THE 99TH PERCENTILE FOR JULY...AND
WILL SUPPORT VERY EFFICIENT RAINFALL PRODUCTION IN THE
THUNDERSTORMS ACROSS THE REGION.

HI-RES MODELS MAY BE A BIT TOO QUICK WITH THEIR DISSIPATION OF
ONGOING ACTIVITY GIVEN THE MODERATE INSTABILITY AVAILABLE AND
ANOMALOUSLY HIGH MOISTURE LEVELS. CURRENT EXPECTATIONS ARE THAT
ISOLATED TO SCATTERED CONVECTION SHOULD BE SUSTAINED THROUGH AT
LEAST 03-04Z AND PERHAPS LONGER.

LAMERS

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

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

LAT...LON   38441597 38251455 37911341 37751241 37131157
            36321212 35841304 35711431 35071514 34511573
            34701681 35741742 36281777 37001844 37641863
            38241805 38141708