MESOSCALE PRECIPITATION DISCUSSION 0042
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
233 AM EDT SAT MAY 18 2013
 
AREAS AFFECTED...NORTHERN MS...NORTH-CENTRAL AL...WESTERN GA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 180630Z - 181230Z
 
SUMMARY...A TRAINING BAND OF CONVECTION IS EXPECTED TO PERSIST
ACROSS PORTIONS OF NORTHERN MS...NORTH-CENTRAL AL...AND WESTERN GA
INTO THE MORNING HOURS, LEADING TO FLASH FLOODING.

DISCUSSION...A LACK OF CIN/A MID-LEVEL CAP NEAR A WEAK STATIONARY
FRONT/BAROCLINIC TROUGH AT THE SURFACE IS ALLOWING CONVECTION TO
FIRE IN ITS VICINITY ACROSS PORTIONS OF NORTHERN MS AND
NORTH-CENTRAL AL.  RECENT RAINS ACROSS THE REGION HAVE LOWERED
FLASH FLOOD GUIDANCE VALUES -- FFGS -- TO 1.5-2 INCHES WITHIN
THREE HOURS' TIME ACROSS A GREAT DEAL OF THIS REGION.  THE 21Z
HRRR AND 12Z NMM MESOSCALE MODEL FOCUSED A SIGNIFICANT PORTION OF
THE HEAVY RAINFALL EXPECTED BETWEEN 09Z-12Z, SHOWING FORECAST
AMOUNTS OF 3-6 INCHES ACROSS AL...WHICH A FEW HOURS OF TRAINING
COULD ACCOMPLISH WITH THE AVAILABLE MOISTURE.  PRECIPITABLE WATER
VALUES -- PWS -- ARE NEAR 1.75 INCHES ALONG THE SURFACE BOUNDARY
AND LOW-LEVEL INFLOW IS GENTLY CONVERGENT INTO THE MS/AL PORTION
OF THE BOUNDARY, WITH MORE ORTHOGONAL FLOW ACROSS THE FRONT
EXPECTED ACROSS WESTERN GA.  THE REGION IS WITHIN AN AREA OF
DIVERGENCE ALOFT BETWEEN TWO WEAK JET MAXIMA, WITH A COLD POOL IN
THE MID-LEVELS ALSO AIDING IN THE PRECIPITATION EFFICIENCY.  THIS
ACTIVITY IS EXPECTED TO PERSIST PAST SUNRISE...WHICH LED TO A SIX
HOUR TIME FRAME BEING USED FOR THIS DISCUSSION.

ROTH


ATTN...WFO...FFC...BMX...HUN...MEG...JAN...

LAT...LON   34199043 34228828 34088562 33698420 32578448 32428658
            32688845 33269007 34199043