MESOSCALE PRECIPITATION DISCUSSION 0358
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
754 PM EDT THU JUL 16 2015
 
AREAS AFFECTED......NORTHERN AND CENTRAL ILLINOIS AND ADJACENT
MO/IA/IN... 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 162355Z - 170555Z
 
SUMMARY...THUNDERSTORMS WITH RAINFALL RATES UP TO 2" AN HOUR ARE
EXPECTED TO MOVE ACROSS NORTHERN AND CENTRAL IL TO ADJACENT IN. 
FLASH FLOODING IS POSSIBLE WHERE CELLS TRAIN.

DISCUSSION...CLUSTERS OF SHOWERS AND THUNDERSTORMS HAVE FORMED ON
THE SOUTHERN EDGE OF A SHARP INSTABILITY GRADIENT WITH MIXED LAYER
CAPE VALUES OF 3-4000 J/KG 
JUST IN ADVANCE OF THE CLUSTERS OF RAINFALL. 

UPSTREAM, THE MODELS INDICATE DEEP SOUTHWEST FLOW WITH A JET MAX
PROGGED BY THE GFS TO BE 50 KT FROM 300 TO 250 MB CROSSING
NORTHERN KS, WITH EXIT REGION DIVERGENCE PROVIDING RISING MOTION.
STRONG DEEP LAYER FLOW OF 45 KT SHOULD RESULT IN STEADY
PROGRESSION OF THE CLUSTERS OF SHOWERS AND STORMS ACROSS NORTHERN
AND CENTRAL IL THIS EVENING...AND THEN CROSSING INTO ADJACENT IN. 

PRECIPITABLE WATER VALUES OF 2-2.2" PER THE LATEST RAP ANALYSIS
AND GFS FORECAST PROVIDE AVAILABLE MOISTURE THAT IS 2 TO 2.5 STD
DEVIATIONS ABOVE NORMAL. 

THUNDERSTORMS ARE EXPECTED TO PERSIST.  THE SOUTHERLY COMPONENT OF
DEEP LAYER SOUTHWEST FLOW WILL BE OFFSET BY A NORTHERLY COMPONENT
OF PROPAGATION...RESULTING IN A EAST MOVEMENT.  CELL TRAINING IS
THE MAIN FLASH FLOOD THREAT...CAUSED BY A SLIGHT INCREASE IN THE
850 HPA INFLOW.  

THE 12Z ARW/NMMB/NSSL WRF AND HIGH RES RAPID REFRESH ALL TARGET
THIS REGION. 
THE AVAILABLE MOISTURE, INCLUDING INFLOW WITH DEWPOINTS IN THE MID
TO UPPER 70S, SUPPORTS HOURLY RAIN RATES UP TO 2".  THE HIGH RES
QPF GUIDANCE SHOWS MAXIMA OF 2-4" OF RAIN IN THIS REGION.   FLASH
FLOOD GUIDANCE VALUES OF 2.5 TO 3 INCHES IN 6 HOURS RESULTS IN
WIDELY SCATTERED LOCATIONS EXPECTED TO EXCEED FLASH FLOOD GUIDANCE
VALUES.

PETERSEN

ATTN...WFO...DVN...ILX...IND...LOT...LSX...

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

LAT...LON   41688862 41208724 40248726 39868876 39809023 
            39959142 40649159 41059133 41679053