MESOSCALE PRECIPITATION DISCUSSION 0466...CORRECTED
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
642 PM EDT TUE JUL 11 2017

CORRECTED FOR CORRECTION FOR LOCATION OF LANGDON

AREAS AFFECTED...NORTHEAST ND & NORTHWEST/CENTRAL MN

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

VALID 112236Z - 120436Z

SUMMARY...THUNDERSTORMS ARE BEGINNING TO DEVELOP ACROSS NORTHEAST
ND.  WITH THE POTENTIAL FOR MESOCYCLONES, HOURLY RAIN RATES UP TO
2" AND LOCAL AMOUNTS TO 4" ARE ANTICIPATED.

DISCUSSION...THE 22Z SURFACE ANALYSIS SHOWS AN OCCLUDED CYCLONE
WITH A 1003 HPA CENTRAL PRESSURE NORTH OF LANGDON ND. 
THUNDERSTORMS HAVE BEGUN TO FORM FROM THE LOW SOUTHEAST TO JUST
NEAR THE CYCLONE'S TRIPLE POINT, WHICH IS ALSO NEAR WHERE THE
DRYLINE INTERSECTS THE FRONTAL BOUNDARIES.  MLCAPE VALUES OF 4000+
J/KG LIE IN THIS REGION.  EFFECTIVE BULK SHEAR OF 25-50 KTS LIES
HERE PER SPC MESOANALYSES.  PRECIPITABLE WATER VALUES WERE
1.4-1.6" AT 14Z PER GPS VALUES AND THE XWI SOUNDING JUST NORTH OF
THE ND/MN/MANITOBA BORDER JUNCTION.  VAD WIND PROFILES SHOW
CONVERGENT SOUTHWEST 850 HPA INFLOW AT 20 KTS.

THE EXPECTATION IS FOR BOUNDARY LAYER MOISTURE CONVERGENCE TO
STRENGTHEN SOUTHEAST OF THESE THUNDERSTORMS NEAR AND NORTHEAST OF
THE WARM FRONT WHICH SHOULD ACT AS THE FOCUS FOR ADDITIONAL
CONVECTION.  WHILE CONVECTION COULD REMAIN ELEVATED, AVAILABLE
INSTABILITY SHOULD KEEP SUCH ELEVATION MINIMAL TO THE EAST OF THE
WARM FRONT.  WITH TIME, INFLOW AT 850 HPA SHOULD EXCEED THE MEAN
850-400 HPA BY UP TO 50%, WHICH SHOULD AID RAINFALL EFFICIENCY. 
THE 20Z RAP BOUNDARY LAYER MOISTURE CONVERGENCE ROUGHLY ALIGNS
WITH THE 12Z-18Z GFS-BASED GALVEZ-DAVISON INSTABILITY INDEX
MAXIMUM AND IS IN THE NEIGHBORHOOD OF THE 12Z WRF NSSL
PRECIPITATION FORECAST, SHOWING A NORTHWEST-SOUTHEAST AXIS ACROSS
NORTH-CENTRAL MN NEAR AND SOUTHEAST OF THE MN LAKES COUNTRY.  THE
BULK SHEAR AVAILABLE SUPPORTS MESOCYCLONES, WHICH CAN YIELD HIGH
RAIN RATES.  THUNDERSTORMS SHOULD EVENTUALLY MOVE SOUTHEAST AT
CLOSE TO 30 KTS, WITHIN THE MLCAPE/MUCAPE INSTABILITY GRADIENT. 
HOURLY RAIN RATES UP TO 2", WITH LOCAL AMOUNTS TO 4", ARE
EXPECTED. 

ROTH

ATTN...WFO...DLH...FGF...MPX...

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

LAT...LON   48829743 48439614 47649478 46429378 45819424
            46119601 47359787 48799933