MESOSCALE PRECIPITATION DISCUSSION 0427
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1058 AM EDT FRI AUG 07 2015
 
AREAS AFFECTED...SRN NEVADA...NRN ARIZONA INTO SERN UTAH 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 071458Z - 072058Z
 
SUMMARY...CONVECTION IS EXPECTED TO EXPAND THROUGH LATE MORNING
INTO THE EARLY AFTERNOON ACROSS PORTIONS OF SRN NEVADA INTO NRN
ARIZONA...EVENTUALLY SPREADING INTO UTAH. GROWING INSTABILITY
COMBINED WITH ANOMALOUSLY STRONG UNIDIRECTIONAL SWLY FLOW SHOULD
ALLOW FOR TRAINING RAINFALL AND POTENTIAL FLASH FLOODING.

DISCUSSION...MORNING WATER VAPOR IMAGERY SHOWED AN ANOMALOUS
CLOSED UPPER LOW MOVING ACROSS CNTRL CALIFORNIA WHICH WAS TIED TO
STRONGER THAN USUAL LOW-MID LEVEL FLOW ACROSS THE SOUTHWEST. BROAD
UPPER DIFFLUENCE WAS ALSO NOTED AHEAD OF THE UPPER LOW ACROSS THE
MPD THREAT AREA. IN THE LOWER LEVELS...THE VWP FROM LAS VEGAS
SHOWED 35 KTS FROM THE SOUTHWEST WHICH CORRELATES REASONABLY WELL
WITH A REGION OF ENHANCED LOW-MID LEVEL FLOW NOTED ON RAP ANALYSES
ACROSS THE REGION WITHIN A LARGER UNIDIRECTIONAL SWLY FLOW IN THE
CLOUD BEARING LAYER. IN ADDITION...MOISTURE CONTINUES TO STEADILY
ADVANCE NWD AHEAD OF THE CLOSED LOW INTO NRN ARIZONA AND SRN
UTAH...AS EVIDENCED BY BLENDED TPW IMAGERY AND THE 1.48 INCH
PRECIPITABLE WATER VALUE NOTED ON THE 12Z VEF RAOB...WHICH IS 2-3
STANDARD DEVIATIONS ABOVE THE MEAN. 

GIVEN THE STRONG DYNAMIC FORCING IN PLACE...AND ABUNDANT MOISTURE
PRESENT...CONVECTION IS DEVELOPING EARLIER THAN WHAT THE USUAL
DIURNAL CYCLE WOULD SUGGEST. GIVEN ONGOING CONVECTIVE ACTIVITY
ACROSS NWRN ARIZONA AND MOSTLY CLEAR SKIES INTO NRN
ARIZONA...EXPECT ADDITIONAL CONVECTION TO DEVELOP INTO THE EARLY
AFTERNOON WITH ADDED DAYTIME HEATING AND GROWING INSTABILITY.
DESPITE RATHER QUICK CELL MOVEMENT OFF TO THE
NORTHEAST...REPEATING CELL MOTIONS ARE EXPECTED WITHIN THE
UNIDIRECTIONAL FLOW WITH CONVECTIVE ACTIVITY LIKELY FEEDING INTO
PORTIONS OF SRN UTAH DURING THE AFTERNOON. THIS TREND IS NOTED IN
SIMULATED REFLECTIVITY ANIMATIONS IN MANY OF THE RECENT HI-RES
MODELS WITH EXPECTED HOURLY RAINFALL RATES OF 1 TO 1.5 IN/HR
POSSIBLE.

OTTO

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

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

LAT...LON   39321051 38820949 37220946 35930987 34701125 
            34301343 34441443 34961513 36131543 37151469 
            38991214 
a