MESOSCALE PRECIPITATION DISCUSSION 0574
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
431 PM EDT THU OCT 15 2015
 
AREAS AFFECTED...PORTIONS OF SOUTHERN CA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 152030Z - 160230Z
 
SUMMARY...SCATTERED CONVECTION DEVELOPING IN A MOISTURE RICH
ENVIRONMENT COULD RESULT IN FLASH FLOODING THROUGH THE EARLY
EVENING.

DISCUSSION...KHNX RADAR SHOWED CONVECTION INCREASING IN COVERAGE
ACROSS PORTIONS OF SOUTHERN CA. MLCAPES OF 1000-15000 J/KG ARE
FEEDING THE DEVELOPMENT...AS LOW LEVEL CIN DECREASES. THE
CONVECTION IS FORMING IN THE PRESENCE OF 1.50 INCH PRECIPITABLE
WATER AIR (WHICH IS BETWEEN FOUR AND FIVE STANDARD DEVIATIONS
ABOVE THE MEAN). KHNX RADAR SHOWED HOURLY RAINFALL RATES BETWEEN
1.50 AND 2.00 INCHES..BUT DRY AIR IN THE MID LEVELS PER RAP MODEL
SOUNDINGS SUGGEST SOME HAIL CONTAMINATION IS POSSIBLE.

AS MID LEVEL HEIGHTS LOWER AND SYNOPTIC SCALE ASCENT
INCREASES...CONVECTION COVERAGE SHOULD BLOSSOM THROUGH AT LEAST
16/00Z. THE MID LEVEL FLOW BECOMES BETTER ALIGNED WITH THE CORFIDI
VECTORS...SUGGESTING THE POTENTIAL FOR TRAINING CELLS...ESPECIALLY
ACROSS THE TERRAIN. 

THERE IS A FAIRLY GOOD SIGNAL IN THE HIGH RESOLUTION GUIDANCE
(SUCH AS THE LATEST HRRR AND 12Z SPC WRF/12Z NSSL WRF) FOR LOCAL 2
INCH RAINFALL AMOUNTS...ESPECIALLY ACROSS THE TERRAIN AND WHERE
TRAINING OCCURS. ONE HOUR FLASH FLOOD GUIDANCE VALUES ARE
GENERALLY AN INCH OR LESS...SO THE THREAT FOR FLASH FLOODING
INCREASES INTO THE EARLY EVENING.

THE MAIN THREAT WINDOW IS EXPECTED BETWEEN 15/22Z THROUGH
16/03Z...WHEN INSTABILITY PEAKS (AND CIN IS SCRUBBED). THE THREAT
SHOULD START TO DIMINISH AFTER 16/03Z. 

HAYES/DEMUTH

ATTN...WFO...HNX...LOX...MTR...

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

LAT...LON   35972038 35721876 34451796 33881800 33941874 
            34261999 35042069