MESOSCALE PRECIPITATION DISCUSSION 0809
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
644 PM EST SAT DEC 31 2016
 
AREAS AFFECTED......CENTRAL AND EASTERN LA...SOUTHERN MS... 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 312343Z - 010343Z
 
SUMMARY...GRADUAL EASTWARD PROGRESSION OF WIDESPREAD HEAVY
RAINFALL MAY RESULT IN ADDITIONAL RUNOFF CONCERNS AND POSSIBLE
FLASH FLOODING THROUGH THE EARLY EVENING HOURS.

DISCUSSION...AIDED BY STRENGTHENING FRONTOGENETICAL FORCING WITHIN
THE RIGHT ENTRANCE REGION OF AN UPPER LEVEL JET STREAK...AREAS OF
HEAVY RAINFALL WILL CONTINUE TO BECOME MORE WIDESPREAD ACROSS THE
CENTRAL GULF COAST AHEAD OF AN AMPLIFYING SOUTHERN STREAM
SHORTWAVE AND ATTENDANT STRENGTHENING LOW-LEVEL MOISTURE
TRANSPORT. THE ROBUST DYNAMICS WILL COUPLE WITH AN INCREASINGLY
FAVORABLE THERMODYNAMIC PROFILE AS ANOMALOUS PRECIPITABLE WATER
VALUES MAX OUT BETWEEN 1.75-2.00 INCHES THIS EVENING ALONG AND
SOUTH OF THE QUASI- STATIONARY SURFACE BOUNDARY. AT THE SAME
TIME...SW-SSW 850 MB FLOW INCREASING TO 40-50 KTS WILL BOOST
MOISTURE FLUX VALUES CLOSE TO 4 STANDARD DEVIATIONS ABOVE NORMAL
OVER THE OUTLOOK AREA...WHILE ALSO FAVORING CONTINUED TRAINING OF
CONVECTION AS THE STRENGTHENING LOW LEVEL FLOW ALIGNS MORE
PARALLEL (AND OF NEARLY THE SAME MAGNITUDE) OF THE MEAN 850-300 MB
FLOW.

DEEP-LAYER INSTABILITY PER THE LATEST SPC MESOANALYSIS AND
SHORT-TERM MODEL PROJECTION IS MARGINAL...WITH MUCAPES EXPECTED TO
CONTINUE AVERAGING AROUND 500 J/KG. HOWEVER GIVEN THE
AFOREMENTIONED FAVORABLE DYNAMICAL AND THERMODYNAMICAL SETUP AND
ENHANCED POTENTIAL FOR CELL TRAINING...EXCEEDANCE OF 3 HOURLY
FLASH FLOOD GUIDANCE VALUES WILL BE POSSIBLE IN SPOTS. THIS IS
SUPPORTED BY THE LATEST HIGH-RES CAM GUIDANCE...INCLUDING THE MOST
RECENT HRRR RUNS...HOWEVER THERE CONTINUES TO BE SOME DISPARITY
AMONG THE MODELS IN TERMS OF THE LATITUDINAL PLACEMENT OF THE
HEAVY RAINFALL AXIS. BASED ON THE LATEST UPSTREAM
TRENDS...CONTINUE TO ANTICIPATE THE EXCESSIVE RAINFALL THREAT TO
EXPAND SOUTHWARD TOWARD THE GULF COAST AND CLOSER TO THE AXIS OF
GREATER INSTABILITY.

HURLEY

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

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

LAT...LON   31508941 31308864 30718850 29968958 29249138 
            29059262 29439292 30409233 31329080