MESOSCALE PRECIPITATION DISCUSSION 0505
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1039 PM EDT SAT JUL 21 2018

AREAS AFFECTED...SOUTHWEST SD

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

VALID 220239Z - 220554Z

SUMMARY...A SHORT TRAINING BAND OF THUNDERSTORMS IS EXPECTED TO
PERSIST ANOTHER 2-3 HOURS.  HOURLY RAIN TOTALS TO 2" WITH LOCAL
AMOUNTS TO 4" ARE POSSIBLE UNTIL IT SHORTENS/FORWARD PROPAGATES.

DISCUSSION...A MESOSCALE LOW MARKS THE WESTERN END OF A SHORT
TRAINING BAND IN SOUTHWEST SD.  DIVERGENCE ALOFT APPEARS TO BE
SPONSORED BY A PAIR OF SHORTWAVES ACROSS CENTRAL AND NORTHEAST MT.
 PRECIPITABLE WATER VALUES ARE ~1.5" PER THE RAPID CITY SD
SOUNDING.  INFLOW AT 850 HPA IS SOUTHEAST AT 20 KTS PER VAD WIND
PROFILES AND RAP MASS FIELDS, WHICH IS IMPORTING MU CAPE VALUES OF
2000-4000 J/KG.  EFFECTIVE BULK SHEAR OF 30-40 KTS HAS HELPED
ORGANIZE THE BAND. INSTANTANEOUS RAIN RATES HAVE RISEN INTO THE
3-4" RANGE PER INFORMATION FROM THE RAPID CITY SD FORECAST OFFICE.
    
BELIEVE THE 00Z NAM CONEST HAS A REASONABLE IDEA OF FUTURE
EXPECTATIONS.  SOME WEST TO EAST TRAINING IS EXPECTED ALONG THE
BAND, WHICH IS EXPECTED TO SAG SLIGHTLY SOUTHWARD WITH TIME WHILE
SHORTENING FROM WEST TO EAST.  ONCE IT MOVES THROUGH THE
INSTABILITY POOL TO ITS SOUTH, IT IS EXPECTED TO EVOLVE INTO A
FORWARD PROPAGATING CONVECTIVE ARC.  UNTIL THEN, HOURLY RAIN
TOTALS TO 2" (SHORTER TERM RAIN RATES UP TO 3-4") WITH LOCAL
AMOUNTS TO 4" APPEAR POSSIBLE.

ROTH

ATTN...WFO...UNR...

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

LAT...LON   44060401 44040337 44030254 43860183 43570103
            43030122 43250314 43570386 43990415