MESOSCALE PRECIPITATION DISCUSSION 0512
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
754 PM EDT WED SEP 23 2015
 
AREAS AFFECTED...EASTERN NE...CENTRAL AND EASTERN SD 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 240000Z - 240600Z
 
SUMMARY...A STRONG LOW LEVEL INFLOW TRANSPORTS DEEP MOISTURE AHEAD
OF A CLOSED LOW OVER NORTHERN NE. CONVECTION DEVELOPING IN THE
STRONG INFLOW COULD PRODUCE FLASH FLOODING.

DISCUSSION...INSTABILITY IS FINALLY BECOMING ESTABLISHED OVER
SOUTHEAST NE (IN THE FORM OF MUCAPE VALUES OF ABOUT 1000
J/KG)..AND CONVECTION IS FIRING IN THE INSTABILITY AXIS. REGIONAL
VWP SHOWED A 20 TO 25 KNOT LOW LEVEL SOUTH SOUTHEAST FLOW IN
PLACE...TRANSPORTING PRECIPITABLE WATER AIR VALUES OF 1.75 INCHES
(WHICH IS BETWEEN TWO AND THREE STANDARD DEVIATIONS ABOVE THE
MEAN) INTO EASTERN NE AND CENTRAL AND EASTERN SD. THE CONVECTION
IS TAPPING THE DEEP MOISTURE...AND KOAX RADAR SHOWED HOURLY
RAINFALL RATES NEAR 1.50 INCHES ACROSS EASTERN NE.

THE LOW LEVEL INFLOW IS FORECAST TO STRENGTHEN TO 35 TO 40 KNOTS
ACROSS EASTERN NE AND CENTRAL AND EASTERN SD THROUGH 24/06Z. THE
LOW LEVEL FLOW ENSURES A CONTINUATION OF HIGH MOISTURE CONTENT AIR
INTO THE REGION....BUT FOR NOW IT APPEARS AS THOUGH INSTABILITY
MAY END UP BEING A LIMITING FACTOR FOR DEEP CONVECTION (AND HEAVY
RAINFALL POTENTIAL). 

THE CLOSED MID LEVEL LOW OVER NORTHERN NE WILL TRUNDLE NORTHEAST
THROUGH THE EARLY MORNING HOURS...PROVIDING SYNOPTIC SCALE ASCENT
FOR HEAVY RAINFALL. THERE IS A GENERAL CONSENSUS AMONG HIGH
RESOLUTION GUIDANCE SOLUTIONS (INCLUDING THE LATEST HRRR/RAP/12Z
WRF ARW AND 18Z REGIONAL GEM) FOR A 2-4 INCH RAINFALL
BULLSEYE...THOUGH THERE IS SOME SPREAD CONCERNING WHERE THIS
OCCURS.

MUCH OF THE HIGH RESOLUTION GUIDANCE SHOWED MUCAPE VALUES
REMAINING BELOW 1000 J/KG ACROSS EASTERN NE AND CENTRAL AND
EASTERN SD THROUGH 24/06Z. HOWEVER...THE STRONG LOW LEVEL INFLOW
OF DEEP MOISTURE...COMBINED WITH SYNOPTIC SCALE ASCENT...COULD
OFFSET THE LACK OF DEEPER INSTABILITY TO PRODUCE A FLASH FLOOD
THREAT.

FOR NOW...THE FLASH FLOOD THREAT IS POSSIBLE. IF THE INSTABILITY
WERE GREATER...THE FLASH FLOOD THREAT WOULD BE GREATER. IN ANY
EVENT...THE FLASH FLOOD THREAT COULD CONTINUE BEYOND THE 24/06Z
TIME FRAME.

HAYES

ATTN...WFO...ABR...FSD...LBF...OAX...UNR...

ATTN...RFC...MBRFC...

LAT...LON   44579718 42909638 40989606 40619718 42639766 
            42759966 44319959