MESOSCALE PRECIPITATION DISCUSSION 0474
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
839 PM EDT TUE JUL 17 2018

AREAS AFFECTED...FAR SERN NV...SRN UT...NWRN AZ

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

VALID 180038Z - 180415Z

SUMMARY...SCATTERED THUNDERSTORMS WILL CONTINUE FOR A FEW
HOURS...INTO THE EARLY EVENING...BEFORE DIMINISHING WITH A LOSS OF
SUNLIGHT. THESE STORMS MAY PRODUCE FLASH FLOODING WITH 1-2 IN/HR
RAIN RATES... PARTICULARLY NEAR BURN SCARS... NARROW CANYONS...
AND URBAN AREAS.

DISCUSSION...GOES-15 IR SATELLITE LOOPS SHOWED A BLOSSOMING OF
COLD CLOUD TOPS NEAR THE UT-AZ BORDER REGION IN THE 23-00Z TIME
FRAME...AND THIS WAS ASSOCIATED WITH AN INCREASE IN SCATTERED
CONVECTION ASSOCIATED WITH THE MONSOON. PRECIPITABLE WATER VALUES
RANGED FROM AROUND 0.8 TO 0.9 INCHES IN THE HIGHER ELEVATIONS AND
RANGES OF CENTRAL UTAH...TO AROUND 1.7 TO 1.8 INCHES IN THE MOHAVE
VALLEY SOUTH OF LAS VEGAS. THESE VALUES WERE GENERALLY AROUND THE
90TH PERCENTILE OF THE CFSR CLIMATOLOGY... ESPECIALLY IN PORTIONS
OF NORTHERN ARIZONA. RAP MODEL ANALYSIS ALSO SHOWED A CORRIDOR OF
MLCAPE VALUES OF 1500 J/KG OR MORE STRETCHING FROM THE SOUTHERN
PORTION OF THE NV-UT BORDER INTO NORTHWEST ARIZONA... AND
EFFECTIVE DEEP LAYER SHEAR WAS ALSO AROUND 20-25 KNOTS. THIS
SHOULD ALLOW FOR SOME STRONG AND ORGANIZED SINGLE-CELL
THUNDERSTORMS OR MULTICELL CLUSTERS EVOLVING ACROSS THE REGION...
EASILY CAPABLE OF PRODUCING LOCALIZED AREAS OF 1-2 IN/HR RAIN
RATES. THROUGH 01-02Z... CONVECTION SHOULD CONTINUE TO ORGANIZE
AND PROPAGATE INTO MORE UNSTABLE AREAS... WITH A GRADUAL WANING OF
CONVECTIVE COVERAGE AND INTENSITY AS THE SUN BEGINS TO SET. FLASH
FLOODING WILL BE POSSIBLE GIVEN THE EXPECTED RAIN RATES.

LAMERS

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

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

LAT...LON   39540961 38590919 37420976 36311020 35701111
            35681193 35131235 34571204 34191265 34371343
            35191408 35641486 36801548 37861516 38391395
            38541251 39101106