MESOSCALE PRECIPITATION DISCUSSION 0563
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
517 PM EDT TUE JUL 25 2017

AREAS AFFECTED...EASTERN SD...SOUTNERN MN

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 252115Z - 260300Z

SUMMARY...INCREASING MOISTURE FLUX AND RAINFALL EFFICIENCY ALONG
WITH TRAINING CORRIDOR ALONG FRONTAL BOUNDARY SUGGEST FLASH
FLOODING POSSIBLE THROUGH LATE EVENING.

DISCUSSION...20Z SFC ANALYSIS DEPICTS AN ELONGATED SURFACE TROF
WITH WEAK INFLECTION NEAR LYMAN COUNTY, SD WITH A WARM FRONT
EXTENDING EASTWARD ACROSS SOUTHERN MN TOWARD THE TWIN CITIES. 
THIS BOUNDARY IS FAIRLY DEEP AS WELL EXTENDING UP THROUGH AT LEAST
850MB WITH CONFLUENT 7H FLOW.  ABOVE THAT THE FLOW BECOMES
INCREASINGLY UNIDIRECTIONAL OUT OF THE DUE WEST SUPPORTING A W-E
CORRIDOR FOR TRAINING GENERALLY PARALLEL TO THE FRONTAL BOUNDARY.

CURRENTLY CONVECTION HAS BROKEN OUT JUST NORTH OF THE SFC FRONTAL
BOUNDARY WITH MORE OF A SEVERE SIGNATURE (PLEASE REFER TO SPC MCD
1420 AND 1421 FOR FURTHER DETAILS).  STILL GIVEN THE ACTIVITY
CONVECTION SHOULD ACT TO MOISTEN THE LOWER TO MID-LEVEL PROFILE
EVEN THOUGH SFC TDS ARE IN THE UPPER 60S TO EVEN MID 70S IN SW MN.
THIS CONCURRENT WITH BROAD 20-25KT SOUTHERLY 850MB FLOW ACROSS NEB
INTO SE SD...RAP FORECASTS SUGGEST RAPID INCREASE OF TOTAL PWS
FROM 1.75" ALONG THE BOUNDARY CURRENTLY OVER 2 TO EVEN 2.25"
FAIRLY QUICKLY.  AS SUCH RAIN RATES WILL INCREASE AS WELL WITH
1.5"/HR CURRENTLY SHIFTING TOWARD 2"/HR.  ONLY POTENTIAL NEGATIVE
FACTOR CURRENTLY IS OUTFLOW BOUNDARIES MAY DISRUPT BEST TRAINING
IN THE NEAR TERM BEFORE BECOMING BETTER ORGANIZED TOWARD 23-00Z.

HI-RES GUIDANCE SHOWS FAIRLY GOOD AGREEMENT IN THE OVERALL
EVOLUTION AND TRACK ALONG THE FRONTAL BOUNDARY BUT WAS POOR WITH
TIMING OF INITIALIZATION (2+ HOURS SLOW) BUT STILL SUGGEST TOTALS
OF 2-3" FROM E SD ACROSS S MN WITH POTENTIAL OF POCKETS AS HIGH AS
5". GIVEN INCREASED DURATION THESE TOTAL MAY EVEN A BIT UNDERDONE.
 THIS LINE OF CONVECTION IS ALSO FAIRLY WELL ALIGNED WITH A SWATH
OF WETTED SOILS RECENTLY WITH AHPS 7 DAYS PERCENT OF NORMAL OVER
300% FROM HURON, SD TO AROUND THE CONFLUENCE OF THE
COTTONWOOD/MINNESOTA RIVER IN SW MN...INCREASING THE LIKELIHOOD OF
FLOODING CONCERNS HERE AS WELL.  ALL ELEMENTS CONSIDERED....A FEW
AREAS OF FLASH FLOODING IS CONSIDERED LIKELY THROUGH 03Z.   

GALLINA

ATTN...WFO...ABR...FSD...MPX...

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

LAT...LON   45299412 45239301 44649287 44179333 43989468
            43979670 44109792 44599833 45099763 45199603