MESOSCALE PRECIPITATION DISCUSSION 0156
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
809 AM EDT THU JUL 11 2013
 
AREAS AFFECTED...PORTIONS OF THE MS/AL BORDER 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 111208Z - 111508Z
 
SUMMARY...CONVECTION IS BEGINNING TO ALIGN ALONG A NORTH-
NORTHWEST/ SOUTH- SOUTHEAST AXIS NEAR THE MS/AL BORDER AND IS
EXPECTED TO PERSIST UNTIL 15Z.  FLASH FLOODING IS POSSIBLE ACROSS
THIS REGION OVER THE NEXT FEW HOURS.

DISCUSSION...AN OUTFLOW BOUNDARY HAS BEEN PUSHING AHEAD OF AN AREA
OF CONVECTION WHICH HAS BEEN DROPPING SOUTH AND WESTWARD FROM
NORTHERN AND CENTRAL ALABAMA OVER THE PAST SEVERAL HOURS.  AS OF
LATE, THE WESTERN END OF THE CONVECTION ACROSS EASTERN MS IS
SHOWING SIGNS OF BACKBUILDING ACROSS NORTHEAST MS, FEEDING OFF AN
AREA OF INSTABILITY WHICH SHOWS UP IN THE 00Z ARW RUN AS AN AREA
OF 2000-3000 J/KG VALUED SURFACE-BASED CAPE.  CORFIDI VECTORS ARE
PARALLEL TO THIS THUNDERSTORM ACTIVITY, INCREASING THE LIKELIHOOD
OF CELL TRAINING.  THE MEAN WIND FLOW IN THE REGION -- IN THE
850-250 LAYER -- IS LIGHT ACROSS EASTERN MS.  INFLOW AT THE 850
HPA LEVEL IS EXPECTED TO BE IN THE 20-25 KNOT RANGE, WHICH IS
LOWER THAN NORMALLY SEEN IN REGIONAL FLASH FLOOD EVENTS.  HOWEVER,
PRECIPITABLE WATER VALUES ARE HIGH -- NEAR 2.25 INCHES -- WHICH
SHOULD LEAD TO HIGH RAINFALL EFFICIENCY.  DIVERGENCE IS PLENTIFUL
AHEAD OF A SHORTWAVE CROSSING THE MISSISSIPPI RIVER AT THIS TIME. 
EARLIER THIS MORNING, MESONET OBSERVATIONS INDICATED 1-1.25 INCHES
OF RAIN WAS FALLING PER HOUR, WHICH WOULD EASILY EXCEED GUIDANCE
ACROSS EASTERN MS WHERE CELLS TRAIN FOR 2-3 HOURS, WHICH IS CLOSER
TO 2-2.5 INCHES IN THREE HOURS.  A QUICK 2-4 INCHES OF RAINFALL
COULD LEAD TO FLASH FLOODING IN THIS REGION.

ROTH

ATTN...WFO...BMX...MOB...MEG...JAN...

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

LAT...LON   33868859 33308831 31688803 31298837 31638911 32798953
            33838922 33868859