MESOSCALE PRECIPITATION DISCUSSION 0397
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1234 AM EDT WED JUL 04 2018

AREAS AFFECTED...WESTERN AND NORTHERN SD...SOUTH CENTRAL ND...

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

VALID 040433Z - 041000Z

SUMMARY...GROWING TREND FOR SW-NE ORIENTED MST
CONVERGENCE/TRAINING CORRIDOR ACROSS SD INTO S ND POSING POSSIBLE
FLASH FLOODING OVERNIGHT.

DISCUSSION...VWP FROM BIS SHOWS RECENT VEERING OF THE FLOW ABOVE
THE BOUNDARY LAYER WITH SLOW INCREASE FROM 20S TO 30KTS FROM THE
SOUTH...THIS ALONG WITH LNX INCREASING TO 40KTS SHOWS THE LLJ WELL
BEGINNING LEADING TO INCREASED MST CONVERGENCE ALONG THE SW TO NE
ORIENTED 850-7H BOUNDARY.  WHILE DEEPEST INSTABILITY WELL EXISTS
FURTHER SOUTHEAST WITH MU CAPES STILL OVER 5000+ J/KG PER RAP
ANALYSIS FROM THE UPPER 70S TDS...IT IS SHOWING SIGNS OF NORTHWARD
AND SLOW WESTWARD SHIFT PER GOES CAPE/LI IMAGERY LOOP.  THE
STRENGTHENED MOISTURE CONVERGENCE AND SLIGHTLY FASTER THAN
EXPECTED HEIGHT-FALLS ALONG SOUTHEAST PERIPHERY OF 110KT 250MB JET
AXIS OVER NE MT/W ND HAS AIDED RECENT RAPID CONVECTIVE DEVELOPMENT
WITH COOLING TOPS FROM MCLEAN,ND TO ZIEBACH,SD COUNTY WITH TOPS
NEARING -70C.  AS THE JET STREAK EXITS, THE 850-7H FRONTAL
BOUNDARY FLATTENS FURTHER FROM CONVECTIVE COMPLEX NEAR/SOUTH OF
THE BLACK HILLS TOWARD THE CENTER OF THE ND/SD BORDER...LEADING TO
POTENTIAL FOR SOME CELLS TO TRAIN OR CROSS TRACK ESPECIALLY IN
CENTRAL AND NORTHERN SD WHERE MID-LEVEL FLOW IS SLIGHTLY WEAKER. 
STILL MEAN CELL MOTIONS WILL BE 30KTS TO THE NORTH OF THE LINE AND
CLOSER TO 20KTS ALONG THE SW TRAILING EDGE.  WITH INCREASED
MOISTURE CONVERGENCE FROM SSELY LLJ SLOWLY VEERING TO SOUTH AND
SSW TOWARD 07-09Z...TPWS WILL CLIMB FROM 1.5 TOWARD 1.75 AND NEAR
2" OVER NE SD ALLOWING FOR MORE EFFICIENT RAIN GENERATION WITH
RATES UP TO 2"/HR BECOMING INCREASINGLY MORE LIKELY WITH TIME. 
THOUGH ANGLE OF INTERSECTION WILL REDUCE WITH THE VEERING OF THE
LLJ TO THE BOUNDARY AFTER 7Z...CELLS PARTICULARLY ON THE SW EDGE
WILL STILL RECEIVE SOLID MOISTURE FLUX TO MAINTAIN HEAVY RAINFALL
THREAT THROUGH EARLY MORNING HOURS.

HI-RES GUIDANCE IS SLOW OVERALL WITH MOST GUIDANCE DELAYED IN THE
CURRENT DEVELOPMENT BY AT LEAST AN HOUR OR SO AND SOME GUIDANCE
LIKE THE NMMB ARE WEST BY AN HOUR AS WELL.  THE CLOSEST GUIDANCE
APPEARS TO BE THE HRRRV3 BUT STILL IS APPEARS A BIT SLOW BUT ALSO
SHOWS GREATER W-E ORIENTATION OF THE FORECAST QPF WITH TOTALS IN
THE 3-5" MAXIMIZED IN NORTH CENTRAL SD...WHICH HAS BEEN A TREND IN
THE OPERATIONAL HRRR AS WELL.  WHILE THE EXACT PLACEMENT REMAINS
UNCERTAIN IN THE GUIDANCE...CURRENT TRENDS WOULD SUGGEST A CENTRAL
PENNINGTON, SD TO LOGAN, ND COUNTY AXIS IS MOST LIKELY WITH
SIMILAR TOTALS SUGGESTED OF 2-4" ISOLATED 5" BY A GOOD MAJORITY OF
THE HI-RES CAMS. WHILE THIS DOES NOT ALIGN WITH THE LOWEST FFG
VALUES THERE ARE MODERATE NEIGHBORHOOD PROBABILITIES TO EXCEED FFG
VALUES AND SUGGEST FLASH FLOODING IS POSSIBLE ACROSS THE
DISCUSSION AREA THROUGH 10Z. 

GALLINA

ATTN...WFO...ABR...BIS...FGF...UNR...

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

LAT...LON   47420048 47349896 46979811 45959774 45369800
            44909868 44570004 43690224 43810377 44670318
            45490236 46000191 47020127