Graphic for MPD #0165
MESOSCALE PRECIPITATION DISCUSSION 0165
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
816 PM EDT SAT APR 29 2017

AREAS AFFECTED...SOUTHWEST OH...CENT & S IND...SOUTHERN
IL..SOUTHEAST MO

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

VALID 300015Z - 300515Z

SUMMARY...MCS/OUTFLOW BOUNDARY TRACKING THROUGH AREAS OF
COMPROMISED GROUND CONDITIONS COMPOUNDING ONGOING FF CONCERNS
THROUGH THE EARLY EVENING.

DISCUSSION...LARGE MCS COMPLEX TUCKED IN ANTICYCLONIC CURVE OF
SYNOPTIC JET WITH EXCELLENT ORIENTATION TO RIGHT ENTRANCE OF 140
KT JET OVER QUEBEC (OPEN TO 70KT PORTION OF THE JET IN MI).  LONG
LIVED UPSCALE GROWING MCV CONTINUES TO MARCH NORTHEAST ACROSS IL
WITH ASSOCIATED SURFACE REFLECTION SOUTH OF DEC AND E OF MTO.  AS
THE SURFACE WAVE AND ASSOCIATED CONVECTIVE SQUALL LINE ADVANCES
WEAKLY CAPPED MLCAPE OF IN EXCESS OF 2000 J/KG CONTINUES TO FEED
VERY STRONG UPDRAFTS REACHING -75C GIVEN FORWARD PROGRESS/MST
CONVERGENCE AT LEADING EDGE OF THE BOUNDARY LEADING TO SEVERE WX
BUT ALSO HIGHLY EFFICIENT RAINFALL PRODUCTION IN ITS PATH
PRODUCING UP TO 1.0" IN LESS THAN 30 MINUTES FOLLOWED BY MODERATE
MCS SHIELD PRECIPITATION TO FURTHER EXACERBATE ANY FLOODING
CONCERNS.  THIS IS FURTHER COMPOUNDED GIVEN THE GROUND CONDITIONS
ARE SATURATED AND MEDIUM TO LARGER STEM CREEKS/RIVERS ARE
CURRENTLY FLOODING...AND 1HR/3HR FFG VALUES ARE AT OR BELOW 1.0".

FURTHER SOUTHWEST/LATER THIS EVENING... AS THE MCV EXITS...THE
OUTFLOW BOUNDARY/COLD FRONT IS BECOMING INCREASINGLY ORIENTED WEST
TO EAST ACROSS THE AREA OF CONCERN.  THIS PLACES THE ENTIRE LINE
NEARLY ORTHOGONAL TO THE BROAD LOW LEVEL SOUTHERLY RETURN FLOW
FROM THE GULF.  THE LLJ IS STRONGER FURTHER WEST ALONG THE LINE
NEARER THE MO BOOTHEEL WITH 850MB FLOW CURRENTLY 30-40KTS THOUGH
EXPECTED TO INCREASE AFTER SUNSET TO 50KTS...WHILE 25-30KT FLOW
OVER SW OH WILL INCREASE TO 30-35KTS.  AS SUCH THERE IS GREATER
CONFIDENCE FURTHER WEST ACROSS S IL/S IND THAN DOWNSTREAM IN OH
AND BEARS WATCHING THOUGH FFG IS LOW THROUGHOUT WESTERN OH.

GIVEN FAIRLY CLEAR SKIES THE TN VALLEY HAS BEEN BUILDING A WELL OF
INSTABILITY TO WORK WITH AND SHOULD SUPPORT BROAD ISENTROPIC
ASCENT OVER THE OUTFLOW BOUNDARY LEADING TO FAIRLY STATIONARY OR
SLOW PROPAGATION INTO THE REMAINING 1000-1500 J/KG MUCAPE IN THE
LATE EVENING HOURS.  CELL MOTIONS GIVEN THE DEEPER CLOUD BEARING
STEERING FLOW ARE MORE FROM THE SW AND WILL ALLOW FOR CELLS TO
TRACK ENEWARD WITH A TRAINING COMPONENT AS WELL.  TO MAKE MATTERS
WORSE...CURRENT TRENDS PLACE THE OUTFLOW BOUNDARY ALONG THE
TRACK/ZONE OF HVY RAINFALL LAST NIGHT.  WHILE THERE IS SOME HOPE
FOR SOUTHWARD PROPAGATION INTO THE FLOW GREATER ASCENT/FORCING
REMAINS NORTH; PROMOTING  LIFE-THREATENING FLASH FLOODING TO OCCUR
IF WORSE CASE SETUP OCCURS.  EVEN IF THE LINE  BECOMES MORE BROKEN
OR SOUTHWARD DRIFTING...FLASH FLOODING WOULD REMAIN LIKELY DUE TO
THE TRAINING AND LOWER FFG VALUES IN THE VICINITY NORTH OF THE
OHIO RIVER.

GALLINA

ATTN...WFO...ILN...ILX...IND...IWX...LMK...LSX...PAH...

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

LAT...LON   40588455 39778386 38798453 38228595 36938901
            36719068 37729094 38308995 39818750 40258721
           


Last Updated: 816 PM EDT SAT APR 29 2017