MESOSCALE PRECIPITATION DISCUSSION 0344
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
505 AM EDT THU JUN 21 2018

AREAS AFFECTED...SOUTHEAST AR...WEST-CENTRAL TO NORTHERN
MS...NORTHERN AL

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 210905Z - 211430Z

SUMMARY...HEAVY SHOWERS AND THUNDERSTORMS OVER THE NEXT FEW HOURS
WITH ENHANCED RAINFALL RATES TO NEAR 2 INCHES/HR WILL RESULT IN
SOME FLASH FLOODING CONCERNS.

DISCUSSION...THE LATEST RADAR IMAGERY SHOWS A RELATIVELY
CONCENTRATED AXIS OF HEAVY SHOWERS AND THUNDERSTORMS MOVING ACROSS
SOUTHEAST AR AND INTO WEST-CENTRAL TO NORTHERN PORTIONS OF MS. THE
ACTIVITY IS FOCUSING AROUND THE SOUTH SIDE OF A DEEP LAYER TROUGH
OVER THE MIDWEST. HOWEVER...IT IS BEING FOCUSED IN PARTICULAR
WITHIN A REGION OF IMPROVING UPPER LEVEL DIVERGENCE ASSOCIATED
WITH MODEST RIGHT-ENTRANCE REGION JET DYNAMICS.

THE CONVECTION IS ALSO BEING AIDED BY THE ARRIVAL OF SOME VORT
ENERGY LIFTING NORTHEAST ACROSS THE LOWER MS VALLEY AND ALSO THE
NORTHEAST TRANSPORT OF DEEP TROPICAL MOISTURE FROM THE WESTERN
GULF COAST REGION. INSTABILITY IS RELATIVELY MODEST...BUT THE
CONVECTION IS GENERALLY TRAVERSING THE NORTH SIDE OF A 500 TO 1000
J/KG MUCAPE GRADIENT IS BEING FURTHER AIDED BY CONVERGENT 850 MB
FLOW.

PWATS ARE NEAR 2.25 INCHES AND THIS IS FAVORING ENHANCED RAINFALL
RATES THAT ARE LIKELY TO EXCEED 2 INCHES/HR WITHIN THE STRONGEST
OF THE CONVECTIVE CORES. THE CLOUD TOPS OVER THE LAST COUPLE OF
HOURS HAVE BEEN GENERALLY STEADY STATE...BUT WITH SOME ADDITIONAL
UPTICK IN FORCING ALOFT OVER THE NEXT COUPLE OF HOURS...THERE MAY
BE SOME COOLING OF THESE CLOUD TOPS AND A BIT OF AN UPTICK IN THE
RAINFALL RATES.

THE LATEST HRRR GUIDANCE SUPPORTS AS MUCH AS 3 TO 4 INCHES OF RAIN
WITH LOCALIZED AMOUNTS PERHAPS APPROACHING 5 INCHES. THE
CONVECTION WILL FOCUS ESPECIALLY ON WEST-CENTRAL AND NORTHERN MS
OVER THE NEXT FEW HOURS...BUT WILL ALSO BECOME MORE NUMEROUS
ACROSS AREAS OF NORTHERN AL AS BETTER FORCING ARRIVES AND
INTERACTS WITH FAVORABLE MOISTURE/INSTABILITY PROFILES ACROSS THE
REGION.

GIVEN THE VERY HEAVY SHORT-TERM RAINFALL RATE POTENTIAL...FLASH
FLOODING IS LIKELY...AND ESPECIALLY FOR ANY URBANIZED AREAS.

ORRISON

ATTN...WFO...BMX...HUN...JAN...LZK...MEG...

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

LAT...LON   34928720 34818577 34098577 33518694 33168833
            32929008 32899075 33019149 33379174 33959123
            34358990 34718842