MESOSCALE PRECIPITATION DISCUSSION 0818
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
314 AM EDT THU SEP 21 2017

AREAS AFFECTED...SOUTHWEST IA...NORTHWEST IL...EXT NORTHEAST MO

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

VALID 210715Z - 211200Z

SUMMARY...BACKBUILDING AND TRAINING CONVECTION WITHIN NEARLY
STATIONARY LINEAR MCS CONTINUES TO POSE FLASH FLOODING RISK
THROUGH EARLY MORNING.

DISCUSSION...GOES-16 6.9UM MID-LEVEL WATER VAPOR CHANNEL DEPICTS
EXITING SHORTWAVE ACROSS ONTARIO WITH SOUTHWESTERLY JET ACROSS
DAKOTAS/N MN ATTM WITH TRAILING TROF FROM THE EASTERN UP BACK TO
SE KS. AT THE SURFACE SURFACE FRONT IS NEARLY STATIONARY BISECTING
WI INTO E IA BEFORE BENDING MORE WESTERLY ACROSS S IA INTO NW
MO...THOUGH ONGOING CONVECTION ACROSS E IA HAS PRODUCED AN OUTFLOW
BOUNDARY THAT HAS MOVED SOUTH AND IS CURRENTLY ORIENTED MORE
EAST-WEST FROM DAVIS COUNTY IA JUST SOUTH OF BRL/GBG BUT NORTH OF
EOK AND MCB AND PROVIDES SOLID ORIENTATION FOR ISENTROPIC ASCENT
FROM 30KT SWLY LLJ.  THE 10.3 UM CLEAR IR CHANNEL DEPICTS THE
STRONG UPDRAFTS/ASCENT WITH NUMEROUS OVERSHOOTING TOPS WITH
COOLING MCS WITH FURTHER SCATTERED TCU/SMALL CBS FURTHER WEST
ALONG THE LINE.

RECENT VWP NETWORK OVER NW MO SUGGESTS EVER SO SLIGHT VEERING WITH
TIME BUT STILL MAINTAINS SOLID STRENGTH OF THE FLOW AT THIS TIME. 
STILL AS THE MAIN WAVE CONTINUES TO DEPART FURTHER NE...LLJ IS
EXPECTED TO WEAKEN AND FURTHER VEER DECREASING ORTHOGONAL
FLOW/ASCENT OVER THE BOUNDARY TOWARD 10-11Z. STILL IN THE
SHORT-TERM 850-7H FLOW REMAINS GENERALLY CONFLUENT ACROSS SE IA
SUPPORTING MEAN ENE CELL MOTION THOUGH WITH STRONGER
INFLOW...PROPAGATION VECTORS HAVE BACKED AND ARE EITHER STATIONARY
OR SUPPORT 5KTS FROM THE NORTHEAST SUGGESTING FURTHER BACKBUILDING
AND TRAINING WITHIN THE OVERALL COMPLEX (AS NOTED WITH UPSTREAM
TCU/SMALL CB IN GOES IR).  SUFFICIENT INSTABILITY REMAINS ALOFT TO
MAINTAIN UPDRAFTS WHILE LLJ PROVIDES MST CONVERGENCE ALONG THE
OUTFLOW BOUNDARY.

GIVEN AVAILABLE MOISTURE RATES OF 1.5-2"/HR ARE LIKELY AND SHOULD
SUPPORT ADDITIONAL 2-4" TOTALS ACROSS SE IA WITH POSSIBLE LOCALES
UP TO 5" THROUGH 12Z.  THIS MAY ALIGN WITH AREAS THAT HAVE ALREADY
RECEIVED 1-2" (THOUGH AREAS OF 2-4" FURTHER NORTH A LIKELY TO BE
SPARED THIS ADDITIONAL 2-3").  THIS IS IN LINE WITH RECENT RUNS
FROM THE ESRL HRRRV3 WHICH HAS BEEN PERFORMING WELL THROUGH THE
EVENT THIS EVENING AS WELL AS OTHER HI-RES GUIDANCE SUCH AS THE
ARW/NMMB THOUGH ALL SHOW A MINOR NORTHWARD BIAS.

GALLINA

ATTN...WFO...DMX...DVN...EAX...ILX...

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

LAT...LON   41838982 41068996 40669036 40429122 40499306
            40889326 41589140