MESOSCALE PRECIPITATION DISCUSSION 0177
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
632 PM EDT SUN MAY 20 2018

AREAS AFFECTED...ERN AR...NW MS...WRN TN...SRN KY

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

VALID 202231Z - 210116Z

SUMMARY...VERY SLOW CELL MOTION COUPLED WITH MODERATE CAPE WILL
LEAD TO ELEVATED FLASH FLOOD POTENTIAL THROUGH MID EVENING.

DISCUSSION...AT 2215Z CONVECTION WAS ONLY LOOSELY ORGANIZED OWING
TO WEAK DEEP LAYER SHEAR. THERE WERE SOME COMPENSATING
FACTORS...HOWEVER...WITH A VERY MOIST AIR MASS RECEIVING HEATING
AND LEADING TO MODERATE CAPE WITH NO INHIBITION...AND WEAKLY
SUPPORTIVE BROAD SCALE 12-HOUR 500-MB HEIGHT FALLS OF AROUND 10-15
METERS OCCURRING THROUGH 06Z. STORMS HAD DEVELOPED IN A MORE
WIDESPREAD FASHION THAN MANY OF THE HI-RES MODELS WOULD HAVE
SUGGESTED...AND IT WAS EVIDENT FROM OBSERVATIONAL TRENDS THAT
OUTFLOWS WILL BE EFFICIENT AT GENERATING NEW CONVECTIVE GROWTH
WITHIN THE CAPE AXIS ALONG THE MISSISSIPPI RIVER AND EXTENDING
WELL INTO TENNESSEE / NASHVILLE AREA AND UP INTO SOUTHERN KENTUCKY
THROUGH EVENING.

SLOW CELL MOTIONS ARE OF PARTICULAR CONCERN HERE...WITH PLACEMENT
NEAR A 700 MB RIDGE CENTER ENSURING WEAK STEERING FLOW AND MEAN
0-6 KM WINDS OF ZERO TO TEN KNOTS...SLOWEST TO THE EAST.
INDIVIDUAL CELLS MAY LAY DOWN AROUND 1 TO 2 INCHES OF RAIN BEFORE
GUSTING OUT...AND CELL MERGERS COULD PRODUCE ISOLATED TOTALS
GREATER THAN 2 INCHES...ALL OCCURRING WITHIN 1 TO 2 HOURS AT ANY
GIVEN LOCATION. ANTECEDENT CONDITIONS ARE SOMEWHAT WET...AND 2
INCHES IN 1 OR 2 HOURS WOULD MEET OR EXCEED FLASH FLOOD GUIDANCE
IN MANY LOCATIONS...SO WE ANTICIPATE A FEW OR SEVERAL MORE FLASH
FLOOD WARNINGS MAY BE NEEDED...ALTHOUGH ON A WIDELY SCATTERED
BASIS.

BURKE

ATTN...WFO...JAN...LMK...LZK...MEG...OHX...PAH...

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

LAT...LON   37778753 37188556 35808677 35348926 34099064
            34149140 34949100 35659002 36818855