MESOSCALE PRECIPITATION DISCUSSION 0404...CORRECTED
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1119 PM EDT TUE JUN 27 2017

CORRECTED FOR NAM CONEST RUN REFERENCED

AREAS AFFECTED...SOUTHWEST MN & VICINITY

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

VALID 280305Z - 280905Z

SUMMARY...THUNDERSTORMS ARE EXPECTED TO DEVELOP AND EXPAND IN
COVERAGE BETWEEN 04Z AND 07Z.  HOURLY RAIN RATES TO 2", WITH LOCAL
AMOUNTS TO 5", ARE EXPECTED.

DISCUSSION...A STRENGTHENING AREA OF LOW PRESSURE IS JUST EAST OF
BISMARCK ND AT THIS TIME.  TO ITS SOUTHEAST, A STATIONARY FRONT IS
SEEN IN SURFACE OBSERVATIONS WHICH APPEARS TO BE CONFIRMED IN THE
MVX RADAR ECHOES TO THEIR WEST.  PRECIPITABLE WATER VALUES OF
0.9-1.3" EXIST HERE PER GPS VALUES.  INFLOW AT 850 HPA IS 35-45
KTS OUT OF THE SOUTH-SOUTHWEST -- 10-15 KTS BEYOND THE MAGNITUDE
OF THE MEAN 850-400 HPA WIND -- WHICH IS CAUSING MUCAPE VALUES TO
RISE NEAR AND EAST OF THE FRONT.  THE UPWIND MUCAPE VALUES ARE IN
THE 500-2000 J/KG RANGE.  EFFECTIVE BULK SHEAR OF 30-50 KTS EXISTS
NEARBY, WHICH IS SHIFTING EASTWARD WITH THE CYCLONE.  DIVERGENCE
ALOFT IS SIGNIFICANT TO THE SOUTHEAST OF AN UPPER LOW IN WESTERN
CANADA, AND AN MCV MOVING INTO THE REGION FROM CENTRAL SD MAY ALSO
AID UPPER DIVERGENCE/INCREASING VORTICITY ADVECTION WITH HEIGHT.

AS INSTABILITY INCREASES AND THE FRONT EDGES EASTWARD, BOUNDARY
LAYER MOISTURE CONVERGENCE IS FORECAST TO INCREASE ACROSS
SOUTHWEST MN AND THE EAST-CENTRAL DAKOTAS WITH TIME, WHICH SHOULD
ACT THE FOCUS FOR THE CONVECTION.  A FEW SHOWERS ACROSS NORTHWEST
IA MAY BE THE BEGINNINGS OF THE EXPECTED ACTIVITY, WHICH SHOULD
BUILD NORTHWESTWARD UP THE BOUNDARY AS MOISTURE VALUES INCREASE TO
1.5-1.75".  BY 06Z, THE INFLOW AT 850 HPA IS EXPECTED TO BE DOUBLE
THE MEAN WIND, WHICH IS A TIME WHEN DEVELOPING CONVECTION SHOULD
EXHIBIT BACKBUILDING CHARACTER.  THE MEAN FLOW ACCELERATES TO THE
VALUES OF THE LOW-LEVEL INFLOW BY 09Z, WHICH SHOULD CAUSE ANY
BACKBUILDING CONVECTION TO CEASE BY THEN. 

THE MESOSCALE GUIDANCE WHICH GOT THE RADAR DEPICTION MOST CORRECT
AT 02Z WERE THE 00Z HRRR AND 18Z NAM CONEST.  THEY SHOW OUTFLOW
BOUNDARIES FROM THE CONVECTION IN THE DAKOTAS SHIFTING EASTWARD
WHICH MAY HELP INITIATE CONVECTION NEAR THE BOUNDARY.  SHOULD ANY
CONVECTION ATTEMPT TO FORWARD PROPAGATE, IT WOULD TO THE SOUTHEAST
AT ~ 20-25 KTS, WHICH CONSIDERING THE BREADTH OF THE INFLOW OVER
THE FRONT COULD LEAD TO SHORT PERIODS OF TRAINING.  THE 18Z SSEO
NEIGHBORHOOD PROBABILITIES OF EXCEEDING THE THREE HOUR FLASH FLOOD
GUIDANCE MAXIMIZE BETWEEN 07Z AND 11Z.  THE BETTER PERFORMING
MESOSCALE GUIDANCE SO FAR, ALONG WITH THE 27/00Z WRF NSSL,
INDICATE THAT LOCAL MAXIMA ~5" ARE MOST LIKELY IN SOUTHWEST MN. 
WITH THE EXPECTED UPTICK IN MOISTURE, HOURLY RAIN RATES UP TO 2"
ARE POSSIBLE WHERE CELLS ATTEMPT TO TRAIN IN SHORT SEGMENTS,
BACKBUILD, OR WHERE MESOCYCLONES TRY TO FORM GIVEN THE DEGREE OF
EFFECTIVE BULK SHEAR EXPECTED.

ROTH

ATTN...WFO...ABR...DMX...FGF...FSD...MPX...

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

LAT...LON   46009682 45899434 44219330 43009428 43649592
            44959668