MESOSCALE PRECIPITATION DISCUSSION 0223
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
937 AM EDT FRI MAY 20 2016
 
AREAS AFFECTED...NRN MS...WRN AND CNTRL TN...SWRN KY 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 201332Z - 201800Z
 
SUMMARY...SHOWERS AND THUNDERSTORMS ARE PERSISTING IN A NARROW
BAND OF FRONTOGENETIC FORCING. 1 TO 3 INCHES OF RAIN ARE POSSIBLE
THROUGH 18Z. FLASH FLOODING IS POSSIBLE.

DISCUSSION...AN AREA OF SHOWERS AND THUNDERSTORMS JUST EAST OF
MEMPHIS, TN HAS BEEN PERSISTENT THIS MORNING ALONG A NARROW BAND
OF LOW-LEVEL FRONTOGENETIC FORCING NORTH OF A SURFACE LOW AND
AHEAD OF A SHORTWAVE MOVING INTO THE MID-MS VALLEY. PRECIPITATION
EFFICIENCY APPEARS TO BE RELATIVELY HIGH IN THIS CONVECTION WITH A
NEARLY SATURATED ATMOSPHERE BELOW 500 HPA AND MODEST DEEP-LAYER
BULK SHEAR. UPPER-LEVEL DYNAMICS ARE BECOMING A LITTLE MORE
FAVORABLE THIS MORNING AS WELL...WITH THE REGION BECOMING SITUATED
IN BETWEEN THE RIGHT ENTRANCE REGION AND THE LEFT EXIT REGION OF
TWO 80 KT JET STREAKS NORTH AND SOUTH OF THE REGION, RESPECTIVELY.

PWAT VALUES ARE CURRENTLY JUST BELOW 1.5" IN THIS REGION AND ARE
FORECAST BY THE RAP TO INCREASE TO SLIGHTLY GREATER THAN 1.5" OVER
THE NEXT FEW HOURS. ADDITIONALLY, MODEST INSTABILITY WILL SLOWLY
INCREASE OVER THE NEXT FEW HOURS AS MUCAPE VALUES INCREASE TO NEAR
500 J/KG BY MIDDAY. THE BEST LOW-LEVEL FRONTOGENETIC FORCING IS
FORECAST BY THE NAM AND GFS TO LIFT NORTHEASTWARD OVER THE NEXT
FEW HOURS, REACHING THE TN/KY BORDER BY MIDDAY. SEVERAL OF THE
LATEST HI-RES MODELS (INCLUDING THE WRF-ARW, WRF-NMM, WRF-NSSL,
AND SPCWRF) AS WELL AS THE SSEO MEAN DEPICT A BAND OF 1 TO 3 INCH
RAINFALL ACCUMULATIONS THROUGH 18Z IN FROM EXTREME NORTHEASTERN MS
TO SWRN KY. THE HRRR AND HRRR-EXPERIMENTAL SHOW A SIMILAR
SCENARIO, ALBEIT SLIGHTLY FARTHER NORTHEAST. FLASH FLOOD GUIDANCE
IS RELATIVELY HIGH, BUT GIVEN THE RELATIVELY HIGH PRECIP
EFFICIENCY, THE POSSIBILITY OF SOME CELL REGENERATION/TRAINING,
AND THE POTENTIAL FOR ISOLATED RATES APPROACHING 2 IN/HR PER CAM
HOURLY PRECIP, A MARGINAL FLASH FLOODING THREAT APPEARS POSSIBLE.

RYAN

ATTN...WFO...LMK...MEG...OHX...PAH...

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

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            35438737 35138807 34888839 34638888 34678926 
            35008937 35688910 36408845 37128756