Graphic for MPD #0245

MESOSCALE PRECIPITATION DISCUSSION 0245
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
120 PM EDT SAT MAY 20 2017

AREAS AFFECTED...SOUTHWEST TN...MS

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 201720Z - 202320Z

SUMMARY...NUMEROUS SHOWERS AND THUNDERSTORMS ARE EXPECTED THIS
AFTERNOON. GIVEN THE INTENSE RAINFALL RATES AND LOCALLY SLOW CELL
MOTION...SOME RUNOFF PROBLEMS AND FLASH FLOODING WILL BE POSSIBLE.

DISCUSSION...EXPERIMENTAL GOES-16 VIS IMAGERY SHOWS A LARGE FIELD
OF CU/TCU ACROSS MUCH OF SOUTHWEST TN...MS AND AL EARLY THIS
AFTERNOON WITH AN ALREADY EXPANDING AXIS OF SHOWERS AND
THUNDERSTORMS IN A N/S FASHION ACROSS THE EASTERN THIRD OF MS AND
INTO PARTS OF WESTERN AL WITH SOME OF THIS NOSING UP INTO
SOUTHWEST TN AS WELL. THE CONVECTION IS ALIGNED QUITE WELL WITH
THE MODESTLY CONFLUENT BUT VERY MOIST SOUTHERLY FLOW COMING IN OFF
THE GULF OF MEXICO...AND IS EXPECTED TO CONTINUE TO EXPAND A BIT
IN COVERAGE OVER THE NEXT FEW HOURS AS DIURNAL HEATING CONTINUES
AND BOUNDARY LAYER INSTABILITY INCREASES. GIVEN THE FAIR DEGREE OF
LOW LEVEL CONFLUENCE...THE ACTIVITY MAY TEND TO ORIENT OR FOCUS A
BIT MORE IN SOME N/S BANDS WHERE IT MAY BE ABLE TO REPEAT OVER THE
SAME AREA. THIS MAY RESULT IN SOME ENHANCED RAINFALL TOTALS AS A
RESULT.

WE WILL ALSO BE WATCHING THIS AFTERNOON THE ARRIVAL OF A
CONVECTIVELY ACTIVE OUTFLOW BOUNDARY WHICH IS NOW COMING INTO
NORTHWEST MS AND ADVANCING SOUTHEASTWARD. THIS LONG-LIVED OUTFLOW
BOUNDARY WITH ORIGINS TO LAST EVENINGS CONVECTION OVER PARTS OF
OK/AR WILL POTENTIALLY MERGE IN A FEW HOURS WITH SOME OF THE
AIRMASS CONVECTION CURRENTLY EXPANDING OVER PARTS OF
CENTRAL/EASTERN MS. THIS WILL ALSO ENHANCE RAINFALL AMOUNTS.

FFG VALUES ARE QUITE HIGH ACROSS THE REGION...SO WIDESPREAD FLASH
FLOODING IS NOT EXPECTED...BUT GIVEN THE PW ENVIRONMENT OF 1.6 TO
1.8 INCHES AND INCREASING INSTABILITY...THE RAINFALL RATES WILL BE
INTENSE AND SHOULD REACH UP OVER 2 INCHES/HR. THIS COUPLED WITH
SOME OF THE AFOREMENTIONED REPEATING CELL ACTIVITY AND
CELL-MERGERS MAY RESULT IN AT LEAST SOME LOCALIZED FLASH FLOODING
OR RUNOFF PROBLEMS. EXPECT LOCALLY AS MUCH AS 2 TO 4 INCHES OF
RAIN WITH ISOLATED HEAVIER AMOUNTS THROUGH THE LATE-AFTERNOON
HOURS AND THIS IS GENERALLY CONSISTENT WITH THE LATEST HRRR
GUIDANCE.

ORRISON

ATTN...WFO...BMX...HUN...JAN...LIX...MEG...MOB...OHX...

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

LAT...LON   35868829 35758788 35348777 34488803 34168812
            32688839 31628850 30968864 30788889 30778939
            30888980 31139025 31699089 32289109 32819109
            33389093 34209036 34758987 35068961 35728882
           


Last Updated: 120 PM EDT SAT MAY 20 2017