MESOSCALE PRECIPITATION DISCUSSION 0443
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1138 PM EDT THU JUL 12 2018

AREAS AFFECTED...SERN SD...SRN MN...NERN NE...NWRN IA

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

VALID 130336Z - 130930Z

SUMMARY...THUNDERSTORMS SHOULD CONTINUE TO AFFECT THE WESTERN CORN
BELT REGION OVERNIGHT WITH LOCALIZED SWATHS OF OVER 3 INCHES OF
RAINFALL POSSIBLE. RAIN RATES IN THE STRONGER STORMS COULD REACH
1-2 IN/HR...AND IF SUSTAINED FOR A COUPLE HOURS THIS COULD LEAD TO
FLASH FLOODING.

DISCUSSION...REGIONAL RADARS SHOWED AN ARC OF CONVECTION EXTENDING
ACROSS MUCH OF THE UPPER MISSISSIPPI RIVER VALLEY AND CENTRAL
PLAINS. A FORWARD PROPAGATING MCS WAS PUSHING INTO WISCONSIN...AND
THE TRAILING CONVECTION NEAR THE MN-IA BORDER REGION WAS SINKING
STEADILY SOUTHEAST (KARX RADAR SHOWED A PROMINENT OUTFLOW BOUNDARY
ACCELERATING AHEAD OF THE CONVECTION). THEREFORE THIS MCS WAS
GENERALLY EXHIBITING A WEAKENING TREND. FURTHER WEST...A BROKEN
LINE OF CONVECTION EXTENDED FROM SW MINNESOTA INTO NRN AND WRN
NEBRASKA. THIS BAND ROUGHLY PARALLELED THE DEEP LAYER MEAN
WINDS...WHICH WAS LEADING TO SOME TRAINING. HOWEVER...THE RAGGED
APPEARANCE OF THE LINE...WITH RELATIVELY LARGE GAPS BETWEEN
INDIVIDUAL CONVECTIVE CLUSTERS...WAS LIMITING THE 2-4HR RAIN RATES
(AND THUS FLASH FLOOD POTENTIAL) SOMEWHAT. IN INDIVIDUAL
CLUSTERS...THE RAIN RATES WERE FAIRLY HIGH (1-2 IN/HR). IF THE
CONVECTION CAN FORM A MORE CONTINUOUS LINE OVERNIGHT THEN FLASH
FLOODING WOULD BECOME MORE LIKELY. THE WESTWARD EXTENT OF THE
GREATEST FLASH FLOOD CHANCES SHOULD BE LIMITED BY THE NEBRASKA
SAND HILLS...WHICH HAVE MUCH HIGHER FLASH FLOOD GUIDANCE AND
GENERALLY TAKE MUCH MORE RAINFALL TO GENERATE FLASH FLOODING.

PRECIPITABLE WATER VALUES ARE CLOSE TO 2 INCHES...WHICH IS ABOVE
THE 99TH PERCENTILE FOR THE SIOUX FALLS AREA FOR JULY. THIS SHOULD
CONTINUE TO SUPPORT HEAVY RAIN RATES WHERE STRONGER CONVECTIVE
CLUSTERS DEVELOP OR EXPAND. THE PRIMARY QUESTION RELATED TO FLASH
FLOOD POTENTIAL IS WHETHER OR NOT THE CONVECTION WILL BECOME MORE
CONTINUOUS OVERNIGHT. THIS DOES NOT SEEM TO BE THE MOST LIKELY
SCENARIO BASED ON CURRENT TRENDS... MODEL FORECASTS SHOWING STEADY
OR SLIGHTLY DECREASING LOW-LEVEL INFLOW THAT WILL VEER WITH
TIME... AND CONVECTIVE MODE SUGGESTED BY CONVECTION-ALLOWING MODEL
REFLECTIVITY FIELDS. THEREFORE...FLASH FLOODING DOES SEEM POSSIBLE
BASED ON FAVORABLE ENVIRONMENTAL CONDITIONS FOR EFFICIENT RAINFALL
PRODUCTION AND CELL TRAINING...BUT THE PROBABILITY AND COVERAGE
MAY BE LIMITED BY CONVECTIVE MODE.

LAMERS

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

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

LAT...LON   45119567 44799447 44409345 43499341 42879434
            42159605 42049743 42569851 42959960 44009865
            44699723