MESOSCALE PRECIPITATION DISCUSSION 0612
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
230 AM EDT SUN OCT 25 2015
 
AREAS AFFECTED...NE LOUISIANA...SE ARKANSAS...N MISSISSIPPI 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 250629Z - 251129Z
 
SUMMARY...NEARLY STATIONARY SHALLOW CONVECTION WITHIN DEFORMATION
ZONE CAPABLE OF RATES TO 1.5"/HR COULD COMPOUND TOTALS FOR SOME
ISOLATED FLOODING CONDITIONS.

DISCUSSION...A WEAKNESS IN FLOW BETWEEN THE EXITING UPPER LEVEL
TROF/UPPER LEVEL POLAR JET STREAK AND APPROACHING UPPER LEVEL
ENERGY HAS ALLOWED A LITTLE WAVE OF IN THE DEEP LAYERED BOUNDARY
ACROSS NE LA/N MS INTO CENTRAL TN.  85-7H LOW LEVEL 20-25KT
REMAINS CONVERGENT BUT DIFFLUENT ALONG THE BOUNDARY...THIS HAS
ALLOWED A NARROW OUTFLOW CHANNEL OF MID-LEVEL MOISTURE AND POCKETS
OF INSTABILITY TO INCREASE TO THE 100-250 J/KG RANGE PARTICULARLY
OVER N MS INTO CENT TN.  WITH ENOUGH CONVERGENCE ALONG THE
BOUNDARY AND SUFFICIENT DIVERGENCE ALOFT...SUPPORTS A SHALLOW
VERTICAL GROWTH OF CONVECTION ACROSS NE LA AND W MS ATTM...WITH
RATES UP TO 1.5"/HR...THOUGH GENERALLY ABOUT 1.0"/HR.  GIVEN THIS
WEAKNESS IN STEERING FLOW WHICH SHOULD REMAIN PERSISTENT FOR THE
NEXT 3-5 HOURS...CELL MOTIONS ARE GENERALLY 5 KTS WITH EITHER ZERO
OR 5 KT NEARLY OPPOSITE PROPAGATION VECTORS TO SUPPORT NEARLY
STATIONARY MOTIONS. THE ALLOWS THE POTENTIAL FOR COMPOUNDED
MODERATE RATES TO REACH 2-4" WITH THE SUPPORT OF NUMEROUS HI-RES
CAMS...SUCH AS THE WRF-NSSL...RECENT HRRR RUNS AND SPC-WRF. THIS
HAS THE POTENTIAL TO NEAR 3-6HR FFG VALUES. ADDITIONAL SUPPORT OF
THE ORIENTATION OF THE CONVECTION IS SUPPORTED NEARLY UNIVERSALLY
THROUGH HI-RES AND GLOBAL MODEL GUIDANCE PROVIDING SOME
CONFIDENCE...BUT WITH MOISTURE PER GPS NETWORK OVER 2.0" IN NE
LA...MOST MODELS HAVE THE POTENTIAL FOR BEING A BIT UNDERDONE.

GALLINA

ATTN...WFO...JAN...LZK...MEG...SHV...

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

LAT...LON   34938818 34628815 34078854 33128978 32669043 
            32439110 32389197 33109241 33989134 34928937