MESOSCALE PRECIPITATION DISCUSSION 0636
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
314 PM EDT SUN AUG 06 2017

AREAS AFFECTED...EASTERN NV...WESTERN/SOUTHERN UT...NORTHERN AZ

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

VALID 061910Z - 070110Z

SUMMARY...MULTIPLE CLUSTERS OF THUNDERSTORMS ARE EXPECTED THIS
AFTERNOON WITH LOCALLY HEAVY RAINFALL. THE SLOW MOVEMENT OF THE
CELLS MAY RESULT IN SOME FLASH FLOODING.

DISCUSSION...THE LATEST CIRA-LPW DATA SHOWS THE BEST CONCENTRATION
OF MOISTURE STRETCHING FROM EASTERN NV EAST ACROSS CENTRAL AND
SOUTHERN UT. THIS COUPLED WITH STRONG DIURNAL HEATING AND LOCAL
OROGRAPHIC FORCING/UPSLOPE FLOW WILL ALLOW CONVECTION TO INITIATE
AND EXPAND WITH TIME THIS AFTERNOON.

THE CONVECTION WILL BE AIDED SOMEWHAT BY THE APPROACH OF AN UPPER
TROUGH OVER NORTHERN CA AND A NOTABLY DIFFLUENT UPPER AIR FLOW
REGIME DOWNSTREAM OVER CENTRAL/EASTERN NV THAT WILL BE ADVANCING
EAST OVER CENTRAL/SOUTHERN UT BY LATER THIS AFTERNOON. JUST LIKE
YESTERDAY...THERE SHOULD BE THE POTENTIAL FOR CLASHING OUTFLOW
BOUNDARIES FOR NEW CONVECTIVE DEVELOPMENT AND ALSO SOME
CELL-MERGER ACTIVITY.

THE MULTI-DAY TREND HAS BEEN FOR A LOWERING OF PWATS WHICH ARE NOW
CLOSER TO 1 INCH MOST AREAS...WITH EXCEPTION TO AREAS OF EASTERN
NV AND SOUTHWEST UT WHERE THEY ARE AS MUCH AS 1 TO 1.2 INCHES. SO
THE RAINFALL RATES BE SOMEWHAT LOWER COMPARED TO PREVIOUS DAYS.
HOWEVER...THE SLOW CELL MOTION...OROGRAPHICS AND POTENTIAL FOR A
COUPLE OF CELL-MERGERS MAY COMPENSATE ENOUGH FOR SOME SCATTERED 1
TO 2 INCH RAINFALL AMOUNTS WITH LOCALLY HEAVIER TOTALS. SOME FLASH
FLOODING WILL BE POSSIBLE AS A RESULT. THE 12Z HIRES MODEL
CONSENSUS ALONG WITH RECENT HRRR GUIDANCE SUGGESTS THE GREATEST
RAINFALL POTENTIAL THROUGH LATE AFTERNOON WILL BE OVER PARTS OF
EASTERN NV AND ESPECIALLY SOUTHERN UT.

ORRISON

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

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

LAT...LON   41191554 41081421 40801332 40251198 39681088
            39361024 38680933 37580906 36040953 35391077
            35401181 35961318 36351348 37081416 37361468
            37421546 37671610 38201612 39141566 40691610