MESOSCALE PRECIPITATION DISCUSSION 0722
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
541 AM EST WED DEC 30 2015
 
AREAS AFFECTED...PORTIONS OF THE CENTRAL GULF COAST 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 301040Z - 301610Z
 
SUMMARY...THUNDERSTORMS NEAR AND NORTH OF A STATIONARY FRONT ARE
STARTING TO TRAIN ACROSS SOUTHEAST LA.  HOURLY RAIN RATES UP TO 2"
COULD LEAD TO FLASH FLOODING.

DISCUSSION...RECENT RADAR AND SATELLITE TRENDS ARE ON AN UPWARD
SWING ACROSS SOUTHEAST LA, WITH AN AREA OF TRAINING STORMS SEEN ON
RECENT IMAGERY SHOWING SHORT STREAKS OF 1.5"/HOUR RAINFALL.  PER
AN SAB/NESDIS BRIEFING, THIS REGION IS AT THE BASE OF A NEGATIVELY
TILTED SHORTWAVE, WITH SATELLITE IMAGERY INDICATING THE ARRIVAL OF
AN UPSTREAM JET STREAK MOVING OUT OF SOUTHERN TX AND NORTHEAST
MEXICO.  A STATIONARY FRONT IS ACTING AS THE FOCUS FOR CONVECTION,
WHICH STRETCHES FROM NEAR BURAS LA TO SOUTHEAST OF MOBILE. 
GPS-BASED PRECIPITABLE WATER VALUES ARE ~1.6" AND 850 HPA INFLOW
FROM THE GULF OF MEXICO IS ROUGHLY 25 KTS OUT OF THE SOUTHWEST PER
VAD WIND PROFILES.

THE WETTER MESOSCALE GUIDANCE, NAMELY THE 00Z SPC WRF, 00Z
WRF4NSSL, AND 00Z NAM CONEST, APPEAR TO BE CAPTURING THIS ACTIVITY
BEST AND ADVERTISE LOCAL AMOUNTS IN THE 3-5" RANGE OVER THE NEXT
SEVERAL HOURS.  THE GFS-BASED GALVEZ-DAVISON INDEX INDICATES THAT
CONVECTIVE COVERAGE ACROSS THIS REGION SHOULD NEARLY DOUBLE
THROUGH 15Z (REACHING 35).  LESS ORGANIZED THUNDERSTORM ACTIVITY
IS EXPECTED TO MOVE NORTHEASTWARD, WITH MORE ORGANIZED CELLS
MOVING MORE TO THE EAST-NORTHEAST PER FORWARD PROPAGATING
CONVECTIVE VECTORS.  THIS OPENS THE POSSIBILITY OF RANDOM CELL
MERGERS.  WITH MOISTURE VALUES THIS HIGH, HOURLY RAIN RATES IN
AREAS OF CELL TRAINING COULD REACH 2", WHICH OVER A FEW HOURS
WOULD CHALLENGE FLASH FLOOD GUIDANCE VALUES IN THE COUNTRYSIDE AND
ARE MORE TROUBLESOME ACROSS URBAN AREAS.  THE ASPECT OF THE
FORECAST WHICH SHOULD KEEP AMOUNTS FROM BECOMING MORE SIGNIFICANT
IS THAT THE GFS/RAP GUIDANCE SHOW SOME EASTWARD PROGRESSION TO THE
FRONTAL BOUNDARY OVER THE NEXT SEVERAL HOURS.  

ROTH

ATTN...WFO...JAN...LIX...MOB...

ATTN...RFC...LMRFC...SERFC...

LAT...LON   31698829 31608662 30448674 29478810 28898947 
            28909100 29449113 30739012