MESOSCALE PRECIPITATION DISCUSSION 0244
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
727 AM EDT SAT MAY 20 2017

AREAS AFFECTED...SOUTHERN IL...FAR SOUTHEAST MO...WESTERN
KY...WESTERN TN...FAR NORTHEAST AR

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

VALID 201125Z - 201525Z

SUMMARY...STRONG THUNDERSTORMS WITH INTENSE RAINFALL RATES TO 2
INCHES/HR ARE EXPECTED OVER THE NEXT FEW HOURS. SOME LOCALIZED
FLASH FLOODING IS POSSIBLE AS A RESULT.

DISCUSSION...VERY COLD CONVECTIVE TOPS ARE MOVING ACROSS SOUTHERN
IL CURRENTLY IN ASSOCIATION WITH A FAIRLY LARGE CLUSTER OF
THUNDERSTORMS. THE ACTIVITY IS FOCUSING WITH THE AID OF A MID
LEVEL SHORTWAVE TROUGH ADVANCING ACROSS THE MID MS VALLEY AND
WITHIN A LARGER SCALE WARM ADVECTION PATTERN. MEANWHILE...AN ARC
OF CONVECTION ASSOCIATED WITH THE EASTWARD ADVANCING OF AN OUTFLOW
BOUNDARY IS NOTED DOWN ACROSS THE MO BOOTHEEL AND NORTHEAST AR.

PWATS THIS MORNING AHEAD OF THE CURRENT CONVECTIVE MASS ARE
RUNNING AS HIGH AS 1.5 TO 1.7 INCHES...WHICH COUPLED WITH THE NOSE
OF ELEVATED INSTABILITY LIFTING UP ACROSS SOUTHEAST MO AND INTO
SOUTHERN IL IS PRODUCING RAINFALL RATES UP TO 2 INCHES/HR.

OVER THE NEXT 2 TO 3 HOURS...EXPECT HEAVY RAINS OVER A LARGE AREA
OF SOUTHERN IL IN PARTICULAR WITH AS MUCH AS 2 TO 4 INCHES OF RAIN
AND ISOLATED HEAVIER AMOUNTS. SOME POCKETS OF HEAVY RAINS WILL BE
EXPECTED FARTHER SOUTH TOO DOWN ACROSS FAR NORTHEAST AR...THE MO
BOOTHEEL AND INTO NORTHWEST TN AND WESTERN KY WHERE OUTFLOW
DOMINATED CONVECTION WILL CONTINUE TO INTERACT WITH A VERY MOIST
AND RELATIVELY UNSTABLE AIRMASS. AT LEAST A LOCALIZED FLASH FLOOD
THREAT EXISTS GIVEN THE INTENSE SHORT-TERM RAINFALL RATES.

THE LATEST HRRR/HRRRX GUIDANCE CONTINUES TO BE WAY TOO SLOW WITH
THE EASTWARD ADVANCE OF THE CONVECTION AND THE SHORTWAVE
ENERGY...BUT EXPECT SOME IMPROVEMENT TO THE CONDITIONS TOWARD LATE
MORNING. WILL CONTINUE TO MONITOR.

ORRISON

ATTN...WFO...ILX...LSX...MEG...PAH...

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

LAT...LON   39858857 39328801 38528788 38148787 37138815
            36218882 35598943 35509008 35729035 36429001
            37648977 38418988 39178984 39758954