MESOSCALE PRECIPITATION DISCUSSION 0493
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
849 PM EDT MON SEP 14 2015
 
AREAS AFFECTED...SOUTHWEST UTAH...NORTHWEST ARIZONA...SOUTHERN
NEVADA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 150048Z - 150518Z
 
SUMMARY...APPROACHING SHORTWAVE TO MAINTAIN CONVECTIVE COVERAGE
WITH 1-1.25"/HR RATES FOR POTENTIAL FLASH FLOODING

DISCUSSION...WV LOOP SHOWS WELL DEFINED SHORTWAVE WITH A SOUTHWARD
EXTENDING TROF EJECTING OUT OF CENTRAL CA INTO WESTERN NV AND
SOUTHERN CA.  THIS HAS ALLOWED FOR SOME INCREASED SHORTWAVE
RIDGING OVER S UT TO ACCENTUATE SPEED DIVERGENCE ALOFT WITH THE
INITIAL ROUND OF CONVECTION SHIFTING/WEAKENING NORTH.  THIS
CONVECTIVE AREA PRODUCED DECENT COOL POOL ACROSS SOUTHERN UTAH
WHICH WILL FOCUS INCREASED CONVERGENCE UPSTREAM OVER SE NV/NW AZ
OVER THE NEXT FEW HOURS ESPECIALLY GIVEN FORECAST INCREASING LOW
LEVEL FLOW TO 25-30 KTS. THIS WILL ADVECT SOME INSTABILITIES AND
ENHANCED LOW LEVEL MOISTURE OUT OF THE COLORADO RIVER VALLEY AND
SEA OF CORTEZ.  SURFACE TDS HAVE BEEN WAFFLING BUT NUMEROUS SITES
OF UPPER 50S TO UPPER 60S REFLECT THIS MOISTURE STREAM.  UPPER
LEVEL SUPPORT SHOULD REMAIN WITH STRONG 70-80KT 3H JET FORECAST TO
SLIDE ACROSS S CA/CENTRAL AZ LEAVING FAVORABLE LEFT EXIT DYNAMICS
ACROSS THE DISCUSSION AREA TO MAINTAIN UPDRAFTS EVEN AFTER SUNSET. 

MUCH OF THE HIGHEST INSTABILITIES MAY HAVE BEEN WORKED OVER A
BIT...HI-RES FORECAST MODELS GENERALLY SUPPORT CONTINUED MUCAPES
OF 500-1000 J/KG THROUGH THE EARLY OVERNIGHT HOURS TO KEEP
CONVECTIVE THREAT MODERATELY HIGH.  LIMITING FACTOR TO FLOODING
THREAT SHOULD BE CELL MOTIONS...ALTHOUGH WITH ENVIRONMENTAL SETUP
RATES AROUND 1-1.25"/HR COULD POSE CONTINUED FLOODING THREAT
PARTICULARLY OVER AREAS ALREADY AFFECTED BY SIMILAR FAST MOVING
BUT EFFICIENT RAINFALL PRODUCTION. STILL OVERALL COVERAGE SHOULD
BE INCREASED GIVEN INCREASED UPPER LEVEL SUPPORT...AS REFLECTED IN
HI-RES MODELS SUCH AS MOST RECENT RUNS OF THE HRRR. 

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

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

LAT...LON   38451198 37901079 37261103 36411181 34861356 
            35091457 35851513 37171403 37891310