MESOSCALE PRECIPITATION DISCUSSION 0675
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
655 PM EDT FRI SEP 16 2016
 
AREAS AFFECTED...NRN AR...SRN MO...SRN IL...ERN OK...FAR WRN KY 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 162254Z - 170224Z
 
SUMMARY...OUTFLOW BOUNDARIES AND SYNOPTIC FORCING WILL CONTINUE TO
DRIFT THROUGH A REGION OF RICH MOISTURE AND MODERATE
INSTABILITY...RAISING THE POSSIBILITY OF ADDITIONAL FLASH FLOODING.

DISCUSSION...WIDESPREAD CONVECTION WAS ONGOING WHERE DIFLUENCE
AHEAD OF UPPER TROUGHING COINCIDED WITH MIXED LAYER CAPE OF AT
LEAST 1000-1500 J/KG. A SHORTWAVE TROUGH EXITING EASTERN OKLAHOMA
WAS ACTING TO BETTER FOCUS ASCENT AND OVERALL COVERAGE/INTENSITY
OF CONVECTION IN PARTS OF OK/AR AND SRN MO. THE SYNOPTIC FLOW AND
A HINT OF COUPLED JET STRUCTURE WOULD SUGGEST A MORE SW-NE
ORIENTATION...WHICH THE HRRR INSISTS ON ADHERING TO...BUT
OBSERVATIONS WERE CLEARLY IN FAVOR OF THE 12Z NSSL WRF AND 18Z NAM
CONUS NEST...WITH THE AXIS FOR NEW THUNDERSTORM DEVELOPMENT
ORIENTED MORE WSW-ENE ALONG OUTFLOW BOUNDARIES...AND DROPPING
SLOWLY SOUTH AND EAST.

THIS MOTION WILL TAKE STORMS INTO AREAS OF HIGHER FLASH FLOOD
GUIDANCE...BUT CERTAINLY SOME OF THE TERRAIN IN THIS REGION IS
PRONE TO FLASH FLOODING...AND CONFIDENCE IS HIGH IN THE EVENT
CONTINUING ANOTHER FEW HOURS GIVEN THE SHORTWAVE AND ASSOCIATED
OMEGA SIGNAL IN THE RAP. INDIVIDUAL CELLS LIFTING MORE NORTHWARD
AND MERGING WITH CELLS ALONG THE SAGGING OUTFLOWS COULD BOOST
HOURLY RAIN RATES ABOVE 1.5 INCHES LOCALLY. MESONET OBSERVATIONS
INDICATED A FEW RATES OF 1.1 TO 1.4 INCHES HAVING BEEN SAMPLED IN
MO/AR. THE BACK EDGE SHOULD COME THROUGH EASTERN OK BY 00Z...BUT
NOT BEFORE CELL MERGERS MAY LEAD TO VERY HEAVY RAIN NEAR SALLISAW
TO FORT SMITH. IN SOUTHERN ILLINOIS AND FAR WESTERN
KENTUCKY...STEERING FLOW WAS A BIT MORE SOUTH TO NORTH...AND
INFLOW WEAKER...BUT DIFLUENT FLOW ALOFT AND PEAK HEATING HAD
CONTRIBUTED TO SCATTERED INITIATION...AND CELLS HERE WILL BE
EQUALLY CAPABLE OF HEAVY RATES...WHILE THE RISK OF FLASH FLOODING
WILL INCREASE WITH MERGERS INTO THE MORE ORGANIZED ACTIVITY NEAR
SAINTE GENEVIEVE TO THE SOUTH OF ST. LOUIS.

BURKE

ATTN...WFO...LSX...LZK...MEG...PAH...SGF...TSA...

ATTN...RFC...ABRFC...LMRFC...MBRFC...NCRFC...OHRFC...

LAT...LON   38458874 37898814 37098902 35169202 34729323 
            34759428 35339516 35979498 36659408 38009051