MESOSCALE PRECIPITATION DISCUSSION 0031
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
918 PM EST THU FEB 22 2018

AREAS AFFECTED...NE AR...SE MO...WRN TN/KY...SRN IL/IN

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

VALID 230217Z - 230717Z

SUMMARY...HEAVIER RAINFALL RETURNING OVER THE NEXT SEVERAL HOURS
THROUGH 08Z. RENEWED FLASH FLOODING / RAPID RUNOFF IS POSSIBLE IN
ADDITION TO ONGOING INUNDATION.

DISCUSSION...THE BREAK BEHIND A DEPARTING SYNOPTIC WAVE WAS
BRIEF...AND THUNDERSTORMS DRIVEN PRIMARILY BY A WARM ADVECTION
PATTERN WERE RETURNING NORTHWARD INTO THE OHIO/MISSISSIPPI RIVER
CONFLUENCE REGION. HEIGHT FALLS WILL OVERSPREAD THE UPPER MIDWEST
TONIGHT...AND IN RESPONSE THE SLOPING FRONTAL ZONE WILL FIND FOCUS
IN THE 850 MB WIND FIELD OVER THE LOWER MS VALLEY...WITH THIS
ENHANCED LOW LEVEL CONFLUENCE / DEEP LAYER ASCENT TRANSLATING
TOWARD THE LOWER OHIO VALLEY THROUGH 08Z.

AT 02Z THIS SYNOPTIC FORCING WAS ALREADY EVIDENCED BY ONGOING
EXTENSIVE THUNDERSTORMS FROM TEXAS TO NORTHEAST ARKANSAS. THE
HRRR/RAP FORECAST SUFFICIENT INSTABILITY...UP TO 250 J/KG...WILL
DEVELOP NORTHWARD IN STEP WITH THE CONVECTION...SUSTAINING
ISOLATED RAIN RATES AS HIGH AS ABOUT 0.70 INCH PER HOUR PER RECENT
DUAL POL ESTIMATES FROM KNQA AND KLZK. BRIEF BOUTS OF TRAINING AS
WELL AS ASSOCIATED STRATIFORM RAIN / STEADY RAINFALL...COULD YIELD
NEW TOTALS OF 1.00 TO 1.50 INCHES IN PLACES THROUGH 08Z. THE 00Z
HRRR LOOKED ESPECIALLY GOOD AT HANDLING THE ORIENTATION AND
INTENSITY OF THE CONVECTION...AND THE 12Z WRF-ARW WAS PERFORMING
SIMILARLY WELL.

THE GRIDDED FLASH FLOOD GUIDANCE ACROSS THIS REGION IS LOW...BUT
MAY NOT BE LOW ENOUGH TO BE FULLY REFLECTIVE OF THE WET ANTECEDENT
CONDITIONS...WITH 2 TO 5 INCHES HAVING FALLEN ALREADY DURING
RECENT EVENTS ACROSS THE ENTIRE DISCUSSION AREA. THUS...THE NEW
RAINFALL MAY VERY WELL PRODUCE FLASH FLOODING IN ADDITION TO
CONTRIBUTING TO FURTHER INUNDATION AND SIGNIFICANT RIVER FLOODING.

BURKE

ATTN...WFO...IND...LMK...LSX...LZK...MEG...OHX...PAH...SGF...

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

LAT...LON   38598665 37468657 35728899 35049064 36169180
            37698993 38538792