MESOSCALE PRECIPITATION DISCUSSION 0033
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
131 AM EST FRI FEB 23 2018

AREAS AFFECTED...KY...ERN AR...WRN TN...SRN IL / IN...SW OH

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

VALID 230631Z - 231231Z

SUMMARY...THROUGH MORNING EXPECT DEEP CONVECTION TO BE SUSTAINED
BY SYNOPTIC SUPPORT AND SUFFICIENT INSTABILITY...LIKELY PRODUCING
FLASH FLOODING. HEAVIEST RAIN RATES AND TOTALS WILL OCCUR FARTHER
WEST TOWARD THE MISSISSIPPI RIVER...BUT SATURATED GROUND MEANS
FLASH FLOODING IS ALSO POSSIBLE FARTHER EAST.

DISCUSSION...MODEL SOLUTIONS DID NOT HAVE A GOOD HANDLE ON THE
DETAILS OF THE CONVECTIVE EVOLUTION OVER THE OHIO VALLEY AND NEAR
THE OHIO/MISSISSIPPI CONFLUENCE. THE 00Z AND 01Z RUNS OF THE HRRR
SEEMED TO BE THE BEST OPTIONS IN EXISTENCE AS OF 06Z. TO SOME
EXTENT THE 00Z WRF-ARW WAS ALSO USEFUL...BUT EVEN THIS GUIDANCE
WAS OVER-EMPHASIZING THE NORTHWARD TRANSPORT OF MOISTURE WITHIN
THE STRATIFORM RAIN SHIELD INTO INDIANA / TIED TO THE DEEP LAYER
SYNOPTIC ASCENT...WHEREAS RADAR AND GAUGE TRENDS INDICATED HEAVIER
RAIN FARTHER SOUTH FROM THE MEMPHIS AREA TO JUST SOUTHWEST OF
LOUISVILLE. WHILE MEAN LAYER FLOW WILL CARRY RAIN
NORTHEASTWARD...THERE APPEARED TO BE A PROPAGATION COMPONENT
FOLLOWING THE UPWIND CORFIDI VECTORS...GENERALLY TOWARD THE EAST
AT 10-15 KNOTS...AS THE CONVECTION ATTEMPTS TO FIND THE AVAILABLE
INSTABILITY.

THE SITUATION HAD BEGUN TO PRESENT ITSELF AS MORE OF A THREAT AT
06Z...WITH CONVECTION BECOMING ALIGNED FAVORABLY FOR
TRAINING...WHILE A SURFACE WARM FRONT CONTINUED TO LIFT NORTHWARD
BRING THE WARM SECTOR CLOSER...NOTING RECENT VEERING OF WINDS TO
SOUTHERLY ACROSS SOUTHERN TENNESSEE.

INSTABILITY WAS SOMEWHAT LIMITED...BUT STORMS IMMEDIATELY DOWNWIND
OF A 500 J/KG MUCAPE REGION STRADDLING THE MISSISSIPPI RIVER...HAD
EXHIBITED DUAL POL ESTIMATED RAIN RATES AS HIGH AS ONE INCH PER
HOUR NEAR MEMPHIS...NOT MUCH LESS THAN THIS IN WESTERN KY...AND
TAPERING TO LESSER AMOUNTS FARTHER EAST. GIVEN A BROAD SCALE
UPSTREAM WAVE...HOWEVER...THE LIFTING WARM FRONT...AND GFS
INDICATION OF AN 850MB MOISTURE TRANSPORT MAXIMUM INTO SOUTHWEST
OHIO BY 12Z...RAIN RATES MAY INCREASE STEADILY WITH EASTWARD
EXTENT OVER TIME. FLASH FLOOD GUIDANCE WAS AS LOW AS 0.50-0.75
INCHES PER HOUR IN SOME AREAS...AND REGARDLESS OF SPECIFIC FFG
VALUES...THE ENTIRE REGION HAD RECEIVED HEAVY RAIN ONLY ONE DAY
PRIOR. WE ESTIMATE ADDITIONAL RAINFALL COULD EXCEED 2.5 INCHES IN
ISOLATED SPOTS THROUGH 12Z...MAINLY WESTERN TN/KY...WITH AMOUNTS
CLOSER TO 1.0-1.5 INCHES ELSEWHERE. EXPECT A HIGH PERCENTAGE OF
SURFACE RUNOFF FROM TRAINING CONVECTION THIS MORNING...AND LIKELY
FLASH FLOODING.

BURKE

ATTN...WFO...ILN...IND...JKL...LMK...MEG...OHX...PAH...

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

LAT...LON   39668359 39088297 38028355 37048503 35578847
            35119069 36039083 38208808 39148648 39608497