MESOSCALE PRECIPITATION DISCUSSION 0440
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
631 PM EDT THU JUL 12 2018

AREAS AFFECTED...SRN MN...WRN WI...ERN SD

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

VALID 122230Z - 130230Z

SUMMARY...CONVECTION DEVELOPING IN A LARGE CAPE / HIGH
PRECIPITABLE WATER ENVIRONMENT WILL PRODUCE PROLIFIC INSTANTANEOUS
RAIN RATES. ANY TRAINING THAT OCCURS WITHIN CONFLUENT LOW LEVEL
FLOW AND OVER CITIES SUCH AS MINNEAPOLIS...WILL LIKELY LEAD TO
FLASH FLOODING.

DISCUSSION...AT 22Z SURFACE WINDS MET NEAR MITCHELL SD...ALONG A
FRONTAL BOUNDARY SAGGING INTO THE NORTHERN PLAINS...AND DIVERGED
WITH CONFLUENT FRONTOGENETICAL FLOW NEAR AND EAST OF LOW
PRESSURE...FROM THE VICINITY OF SIOUX FALLS TO THE WESTERN AND
NORTHERN SUBURBS OF MINNEAPOLIS. RADAR TRENDS SHOWED EXPLOSIVE
THUNDERSTORM GROWTH ALONG THIS LINE...AND THE ACTIVITY WILL BE
SUPPORTED THIS EVENING BY BOTH EXTREME INSTABILITY / SFC-BASED
CAPE 4000 J/KG-PLUS FUELED BY MID 70S SFC TD / AND FAVORABLE
SYNOPTICS.

MID LEVEL CLOUDS IN VISIBLE SATELLITE IMAGERY WERE INDICATIVE OF
AN INFLECTION POINT OVER SOUTH CENTRAL SD...WITH THE DIFLUENT JET
ENTRANCE REGION DOWNSTREAM...COINCIDING WITH THE ERUPTION OF
CONVECTION ALONG THE FRONT. THIS FORCING...ALONG WITH CONFLUENT
850-700 MB FLOW...AND CORFIDI VECTORS FOR FORWARD PROPAGATION
WHICH DEVIATE VERY LITTLE FROM THE MEAN 0-6 KM WINDS...WILL SET
THE STAGE FOR A FEW LOCAL EPISODES OF TRAINING CELLS. THE
SITUATION SHOULD EVENTUALLY YIELD WEST TO EAST FORWARD PROPAGATION
PER THE BETTER PERFORMING GUIDANCE / NSSL WRF AND WRF-ARW / BUT
THE CONCERN IS THAT THE TANDEM OF EXTREME CAPE WITH PRECIPITABLE
WATER VALUES ABOVE 1.75 INCHES WILL ALLOW FOR EXTREME SHORT TERM
RAIN RATES OVER 3 INCHES PER HOUR. GIVEN THAT THE INITIAL
CONVECTION - PRIOR TO COLD POOL FORMATION - IS DEVELOPING ACROSS
THE TWIN CITIES...IT WOULD APPEAR THAT FLASH FLOODING IS LIKELY IN
THE CITY...AND POSSIBLE ELSEWHERE WITHIN THE OUTLINED AREA.

BURKE

ATTN...WFO...ARX...DLH...FSD...MPX...

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

LAT...LON   45739240 45619122 45079075 44189116 43639526
            43569732 44219745 44349664 44629525 45529388