MESOSCALE PRECIPITATION DISCUSSION 0480
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1009 PM EDT WED JUL 18 2018

AREAS AFFECTED...PORTIONS OF NE/SD/IA

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

VALID 190208Z - 190808Z

SUMMARY...BACKBUILDING AND MERGING CONVECTION ACROSS THE REGION
SHOULD BE CAPABLE OF PRODUCING HOURLY TOTALS TO 2" AND LOCAL
AMOUNTS TO 4" OVER THE NEXT SEVERAL HOURS.

DISCUSSION...AN UPPER LOW IS SITUATED NEAR THE WESTERN BORDER OF
THE DAKOTAS, WHILE A PAIR OF SURFACE LOWS SPIN ACROSS NORTHERN NE
AND SOUTHERN SD.  ACTIVE CONVECTION CONTINUES WITHIN A DIVERGENT
AREA ALOFT ACROSS SD AND NE WITHIN THE WARM ADVECTION PATTERN EAST
OF THE DEEP LAYER LOW.  PRECIPITABLE WATER VALUES OF ~1.6" LIE
ACROSS THE AREA PER NEARBY GPS DATA AND THE OAX/VALLEY NE
SOUNDING.  INFLOW AT 850 HPA IS CONVERGENT AT 10-15 KTS. 
EFFECTIVE BULK SHEAR OF 30-50 KTS HAS LED TO SUPERCELL STRUCTURES
WITHIN THE CONVECTION, WHICH EVEN ACCOUNTING FOR HAIL
CONTAMINATION, APPEARS TO BE YIELDING 2" AN HOUR TOTALS. MU CAPE
VALUES OF 500-3000 J/KG EXIST IN THIS AREA.

THE MESOSCALE GUIDANCE SUGGESTS THAT AREAL COVERAGE OF THE
CONVECTION SHOULD BE PEAKING NOW.  HOWEVER, INFLOW AT 850 HPA IS
EXPECTED TO RAMP UP OVERNIGHT, WHICH COULD LEAD TO EITHER A SLIGHT
UPTICK IN COVERAGE AFTER CIN DEVELOPS THIS EVENING OR CONTINUE
CELL BACKBUILDING FOR A WHILE LONGER.  CIN DEVELOPMENT ALONG WITH
EASTWARD MOVEMENT OF THE DEEP LAYERED LOW SHOULD ALLOW FOR SOME
EASTWARD SHIFT IN CONVECTION OVERNIGHT.  THE 700 HPA 12C ISOTHERM
IS EXPECTED TO ACT AS THE SOUTHWEST FRINGE OF THE BROADER
CONVECTIVE COVERAGE.  THE GUIDANCE HAS A WIDELY SCATTERED
SIGNATURE WITH LOCAL AMOUNTS OF 3-4" BETWEEN NOW AND 08Z.  THE
HEAVY RAIN THREATS HERE ARE MESOCYCLONE DEVELOPMENT, BACKBUILDING,
CELL MERGERS, AND THE POSSIBILITY OF MULTIPLE CONVECTIVE ROUNDS. 
HOURLY RAIN TOTALS TO 2" SHOULD CONTINUE TO BE AN ISSUE.  COVERAGE
OF HEAVY RAIN WITHIN THE DEPICTED AREA IS EXPECTED TO BE MORE
SCATTERED/ISOLATED THAN USUAL FOR AN MPD.

ROTH

ATTN...WFO...ABR...DMX...FSD...GID...LBF...OAX...TOP...UNR...

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

LAT...LON   44609840 43919650 42809532 41559567 40769648
            39949770 40329857 42200006 43040006