MESOSCALE PRECIPITATION DISCUSSION 0469
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
348 AM EDT WED JUL 12 2017

AREAS AFFECTED...SOUTHEAST MN...CENTRAL/SOUTHERN WI...NORTHERN
IL...SOUTHERN LOWER MI...NORTHERN IN...NORTHERN OH

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 120745Z - 121345Z

SUMMARY...WIDESPREAD HEAVY SHOWERS AND THUNDERSTORMS WILL CONTINUE
THROUGH DAWN WHILE EXPANDING GRADUALLY OFF TO THE EAST. INTENSE
RAINFALL RATES WILL CONTINUE TO FOSTER FLASH FLOODING...WITH
SIGNIFICANT AND POSSIBLY LIFE-THREATENING FLASH FLOODING
CONDITIONS WHERE VERY HEAVY RAINFALL HAS ALREADY OCCURRED.

DISCUSSION...AN EXTENSIVE AXIS OF SHOWERS AND THUNDERSTORMS
CONTINUES TO FOCUS ALONG AND JUST NORTH OF WHAT IS NOW A
QUASI-STATIONARY FRONT DRAPED FROM NORTHEAST IA EAST ACROSS
NORTHERN IL...NORTHERN IN AND NORTHWEST OH. THE CONVECTION
CONTINUES TO BE FOSTERED BY A RATHER STRONG WARM
ADVECTION/ISENTROPIC LIFT PATTERN WITH A 40 TO 50 KT SOUTHWEST LOW
LEVEL JET INTERACTING WITH AND OVERRUNNING THE AFOREMENTIONED
FRONT. MODERATE TO STRONG INSTABILITY AND HIGH PWATS TO NEAR 2
INCHES CONTINUE TO POOL UP ALONG AND OVER THE FRONT...WHICH IS
HELPING TO CONTRIBUTE TO ORGANIZED CLUSTERS OF BACKBUILDING
CONVECTION AND EXTREMELY INTENSE RAINFALL RATES.

RAINFALL RATES OF 2 TO 3 INCHES/HR HAVE BEEN OBSERVED...AND
CURRENTLY THE WORST CONDITIONS ARE NOTED OVER GENERALLY SOUTHWEST
WI JUST EAST OF THE WI/IA BORDER AND ALSO FARTHER EAST OVER
SOUTHEAST WI TO THE WEST AND SOUTH OF MILWAUKEE AND ALSO SOUTH
DOWN INTO NORTHEAST IL NEAR AND WEST OF THE WAUKEGAN AREA. ALREADY
IN SOME CASES AS MUCH AS 8 INCHES OF RAIN HAVE OCCURRED...AND
ADDITIONAL ROUNDS OF STRONG THUNDERSTORM ACTIVITY ARE EXPECTED
OVER THE NEXT FEW HOURS LEADING UP TOWARD THE DAWN TIME FRAME
GIVEN THE APPROACH OF A ROBUST UPSTREAM SHORTWAVE TROUGH AND
PERSISTENT WARM ADVECTION ENHANCING THE MOISTURE AND INSTABILITY
TRANSPORT.

SEVERE AND POTENTIALLY LIFE-THREATENING FLASH FLOODING IS EXPECTED
FOR THESE AREAS...AND PEOPLE ACROSS EXTREME NORTHEAST
IA...SOUTHWEST TO SOUTHEAST WI AND FAR NORTHEAST IL SHOULD CLOSELY
MONITOR THE ADDITIONAL RAINFALL. AN ADDITIONAL 3 TO 6 INCHES OF
RAIN IS POSSIBLE LOCALLY...WITH SOME LOCATIONS SEEING STORM TOTALS
POSSIBLY IN EXCESS OF 10 INCHES THROUGH 12Z. THE URBAN CORRIDORS
WILL BE EXTREMELY SUSCEPTIBLE TO AN EMERGENCY LEVEL FLASH FLOOD
EVENT.

FARTHER EAST ACROSS SOUTHWEST LOWER MI...FAR NORTHERN IN AND INTO
NORTHWEST OH...THE THUNDERSTORM ACTIVITY HAS BEEN ON THE INCREASE
OVER THE LAST COUPLE HOURS AS WARM ADVECTION ASSOCIATED WITH THE
LOW LEVEL JET INCREASES AND ENHANCES THE THERMODYNAMIC ENVIRONMENT
AS WELL. UPSTREAM SHORTWAVE ENERGY APPROACHING THE ENTIRE REGION
IS ALSO FOSTERING AN UPTICK IN UPPER LEVEL ASCENT/FORCING TO HELP
SUSTAIN THE CONVECTIVE DEVELOPMENT.

ASIDE FROM THE ALREADY HARD HIT AREAS OF FAR NORTHEAST
IA...SOUTHERN WI AND AND NORTHEAST IL...THERE WILL BE A GRADUALLY
GROWING THREAT FOR FOCUSED CONVECTION AND HEAVY RAINFALL FOR AREAS
OF ESPECIALLY SOUTHERN LOWER MI AND INTO NORTHWEST OH OVER THE
NEXT FEW HOURS WITH THESE AREAS SEEING THE POTENTIAL FOR 2 TO 4
INCHES OF RAIN JUST THROUGH ABOUT THE 12Z TIME FRAME ALONG WITH
ISOLATED HEAVIER AMOUNTS WHERE SOME BACKBUILDING OF CELLS AND
BRIEF CELL-TRAINING MAY OCCUR. THIS IS CONSISTENT WITH THE BETTER
PERFORMING 00Z NSSL-WRF AND THE LATEST HRRRX GUIDANCE. SOME OF
THESE AREAS HAVE SEEN LOCALLY HEAVY RAINFALL OVER THE LAST COUPLE
OF DAYS AND SO THE ANTECEDENT CONDITIONS ARE QUITE WET HERE. THUS
THESE AREAS WILL BE PRONE TO FLASH FLOODING CONCERNS AS WELL GOING
PAST DAWN.

ORRISON

ATTN...WFO...APX...ARX...CLE...DLH...DTX...DVN...GRB...GRR...
ILN...IWX...LOT...MKX...MPX...

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

LAT...LON   45859168 45488964 44578690 43828502 43208380
            42648264 41778156 40948125 40378252 41378579
            41728772 41778829 42078945 42709089 43829230
            44709286 45609268