MESOSCALE PRECIPITATION DISCUSSION 0565
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
614 PM EDT TUE JUL 25 2017

AREAS AFFECTED...NORTH CENTRAL NEB...SOUTHEAST SD

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

VALID 252215Z - 260315Z

SUMMARY...DEVELOPING LOW TO MID-LEVEL STACKED LOW WILL FOCUS
STEADY MST CONVERGENCE WITH LITTLE CELL MOTION AND REDEVELOPMENT
ALLOWING FOR POCKETS LONG DURATION HEAVY RAINFALL LEADING TO
POTENTIAL FLASH FLOODING.

DISCUSSION...22Z SFC ANALYSIS DEPICTS A WELL DEFINED FRONTAL ZONE
EXTENDING FROM CENTRAL SD TOWARD AN INFLECTION NEAR ICR IN S
CENTRAL SD AND FURTHER EXTENDING TOWARD THE DEEPER 1007MB LOW NEAR
BFF WITH WEAK TO MODEST DRY LINE EXTENDING DUE SOUTH TO JUST WEST
OF THE CO/KS BORDER.

EVENTUALLY AFTER 00Z THE LOW WILL BEGIN TO CLOSE OFF FROM THE
SURFACE UPWARDS THROUGH 850MB TO 7H BY 05/06Z OVER THE NEB
PANHANDLE.  THIS ORIENTATION/DEEPENING WILL SUPPORT 20KT SOUTHERLY
LLJ TO REMAIN FAIRLY CONSISTENT WHILE STRENGTHENING TO 30-35KTS
SUPPORTING CONSISTENT STRONG MST CONVERGENCE ALONG THE NW EXIT
REGION NEAR THE INFLECTION ACROSS N CENTRAL NEB/S SD THROUGH THE
EVENING. EFFECTIVELY THE WARM CONVEYOR BELT SPLITS/ASCENDS NEAR
THE FRONTAL BOUNDARY INTO A STRONG LOW LEVEL DEFORMATION ZONE WITH
THE WESTERN BRANCH BREAKING AS AN EFFECTIVE TROWAL.  THIS
ALIGNMENT WILL SUPPORT FAIRLY CONTINUOUS BACKBUILDING/SLOW CELL
MOTIONS ACROSS THE NORTHERN SAND HILLS THROUGHOUT THE REMAINDER OF
THE EVENING TOWARD OVERNIGHT HOURS.

IN THE UPPER LEVELS STRONG JET OVER THE DAKOTAS TURNS SLIGHTLY
ANTICYCLONICLY OVER MN/IA WITH STRONG GRADIENT OF THE JET OVER THE
AFFECTED AREA ALLOWING FOR EXCELLENT SUPER-GEOSTROPHIC RIGHT
ENTRANCE LEVEL OUTFLOW FOR THESE CELLS TO MAINTAIN THEMSELVES AS
WELL. 

INITIALLY THESE CELLS WILL SHOW VERY STRONG SEVERE SIGNATURES (SEE
SPC MCD 1420 FOR ADDITIONAL DETAILS) GIVEN FAIRLY DRY MID-LEVELS
THOUGH WITH PERSISTENCE AND MST FLUX FROM WARM CONVEYOR (SFC/850MB
TDS OF MID TO UPPER 60S) TO MOISTEN THE OVERALL PROFILE...RAIN
RATES WILL INCREASE IN INTENSITY AND GIVEN REDEVELOPMENT
POTENTIAL.  HI-RES CAMS SUGGESTIONS OF 3-6HR TOTALS OVER 3-4" SEEM
PLAUSIBLE AND GIVEN CLUSTERING...CONFIDENCE IS INCREASED AS WELL.
HOWEVER...LIMITING FACTOR TO FLASH FLOODING WILL OBVIOUSLY BE THE
GROUND CONDITIONS IN THE SAND HILLS THAT ARE LIKELY TO ABSORB THIS
MAGNITUDE THERE STILL REMAINS A POSSIBILITY OF FLOODING IS
NON-ZERO ESPECIALLY IN/NEAR URBAN CENTERS.

ACROSS SE SD...CLOSER PROXIMITY TO MID TO UPPER LEVEL JET WILL
ALLOW FOR CELLS TO PROPAGATE EASTWARD TO AMELIORATE FLOODING
CONCERNS...THOUGH WITH SOME ABILITY FOR BACKBUILDING AND REPEAT
TRACKS HERE AS WELL...FLASH FLOODING IS CONSIDERED POSSIBLE HERE
AS WELL.  

GALLINA

ATTN...WFO...ABR...FSD...LBF...UNR...

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

LAT...LON   44029825 43739681 43179808 42679940 41900212
            42790264 43160142 43829928