MESOSCALE PRECIPITATION DISCUSSION 0421
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
240 PM EDT SUN JUL 08 2018

AREAS AFFECTED...UTAH...SRN NEVADA...NWRN ARIZONA

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

VALID 081838Z - 090030Z

SUMMARY...SCATTERED THUNDERSTORMS ARE EXPECTED TO DEVELOP THIS
AFTERNOON FROM THE HIGH DESERT REGIONS OF SRN NEVADA AND NWRN
ARIZONA INTO CENTRAL UTAH. THE STORMS ARE LIKELY TO INITIALLY
DEVELOP ALONG TERRAIN FEATURES AND THEN MAY BUILD INTO SURROUNDING
AREAS. RAIN RATES MAY REACH AROUND 1 IN/HR ON A VERY LOCALIZED
BASIS WHICH COULD LEAD TO FLASH FLOODING.

DISCUSSION...AS OF 18Z SCATTERED CONVECTION WAS INITIATING ALONG
THE RANGES OF CENTRAL UTAH AND EVEN INTO A FEW PLACES IN ARIZONA
AND NEVADA SUCH AS THE KAIBAB PLATEAU AND THE SHEEP RANGE.
CONVECTION SHOULD CONTINUE TO BUILD DURING THE AFTERNOON IN THE
PRESENCE OF MARGINAL INSTABILITY (MLCAPE AROUND 500-1000 J/KG) AND
PRECIPITABLE WATER VALUES AROUND OR ABOVE THE 90TH PERCENTILE
(GENERALLY AROUND 1 INCH). THE TALL AND NARROW CAPE PROFILES
SHOULD PROMOTE RELATIVELY WEAK UPDRAFTS BUT FAIRLY EFFICIENT
RAINFALL PRODUCTION. CIRA LAYER PW PRODUCTS SHOW AN ENHANCEMENT IN
THE 500-300MB LAYER OVER THIS SAME REGION WITH AROUND 5MM (0.2
INCHES) PW IN THAT LAYER. THIS IS SUGGESTIVE OF DEEP SATURATED
PROFILES AND MAY ACT TO LIMIT DRY AIR ENTRAINMENT IN THE
RELATIVELY WEAK UPDRAFTS. THE REGION WAS ALSO NEAR AN UPPER LEVEL
RIDGE AXIS...WITH A MINIMUM IN THE MEAN WIND SPEEDS
(850-200MB)...GENERALLY LESS THAN 10 KNOTS. THEREFORE...
CONVECTION SHOULD GENERALLY BE SLOW-MOVING AND GIVEN THE DEEP
MOIST PROFILES...THE ENVIRONMENT APPEARS TO BE REASONABLY
FAVORABLE FOR FLASH FLOODING. HOWEVER...GIVEN THE SCATTERED NATURE
OF CONVECTION...ANY FLOODING SHOULD BE LOCALIZED.

FLASH FLOODING WOULD BE MOST LIKELY IN SMALL NARROW BASINS IN
AREAS OF TERRAIN...OR PERHAPS THE SLOT CANYON REGION OF SOUTHERN
UTAH...AS WELL AS ANY URBAN AREAS.

LAMERS

ATTN...WFO...FGZ...GJT...LKN...RIW...SLC...VEF...

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

LAT...LON   41151003 40500982 38561092 36811167 34891109
            34471272 35051428 36481550 38201465 39571295
            41001152