MESOSCALE PRECIPITATION DISCUSSION 0670
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
542 PM EDT THU SEP 15 2016
 
AREAS AFFECTED...EASTERN NEB...NORTHWEST IA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 152145Z - 160315Z
 
SUMMARY...FAVORABLE ENVIRONMENT FOR BACKBUILDING WITH SOME
TRAINING OF CONVECTION.

DISCUSSION...CONVECTIVE DEVELOPMENT HAS SPROUTED ALONG AND
NORTHEAST OF DEVELOPING WARM FRONT ACROSS E NEB INTO NW IA ON
EITHER SIDE OF THE CONVECTIVELY REINFORCED OUTFLOW BOUNDARY FROM
EARLY MORNING MCS.   STRONG 850MB FLOW/MST FLUX ACROSS E NEB
TOWARD EXITING WAVE SUPPORTS SUFFICIENT ISENTROPIC WAA ASCENT TO
MAINTAIN CONVECTION COINCIDENT WITH MODERATE ENVIRONMENTAL
PARAMETERS (2000 J/KG MLCAPES AND 1.6" TPWS) FOR STRONG UPDRAFTS
AND RAINFALL GENERATION/EFFICIENCY.  RATES OVER 1.5"/HR ARE LIKELY
WITH SOME ISOLATED RATES REACHING 2 OR 2.25" AT TIMES. UPPER LEVEL
JET PATTERN IS IDEAL FOR WEDGE TYPE MCS TO DEVELOP AS CYCLONICALLY
CURVED 70KT POLAR JET FROM NE CO THROUGH E SD ALONG WITH
ANTICYCLONIC 70KT SUBTROPICAL JET ACROSS E KS/N MO SUPPORT
EXCELLENT DIFFLUENCE ALOFT...AND WITH HEIGHT FALLS UPSTREAM
SUPPORT A BACK BUILDING NATURE TO CONVECTION.  RAP PROPAGATION
VECTORS SUPPORT THIS WITH WEAK SUB-10KT VALUES ACROSS THE AREA BY
01-03Z AS NEXT SHORTWAVE APPROACHES. THIS WILL ALSO SUPPORT FAIRLY
UNIDIRECTIONAL FLOW IN THE CLOUD BEARING LAYER TO SUPPORT SOME
TRAINING OF UPSTREAM REDEVELOPMENT COMPOUNDING LOCAL RAINFALL
TOTALS. THIS EVOLUTION IS SUPPORTED BY HI-RES CAMS SUCH AS THE
HRRR/ARW/NMMB PROVIDING CONFIDENCE IN 3-5" TOTALS THROUGH 03Z.
GIVEN LOWER FLASH FLOOD GUIDANCE VALUES (1.5"/1HR AND 2.5"/3HR)
COULD EXPECT SOME FLASH FLOODING TO OCCUR PARTICULARLY IN FAVORED
TRAINING SW TO NE CORRIDORS ACROSS E CENTRAL NEB INTO NW IA.

JUST SOUTH OF THE MN BORDER IN NORTHERN IA...STRONG ISENTROPIC
ASCENT OVER THE REINFORCED OUTFLOW BOUNDARY SHOULD BE MAINTAINED
THROUGHOUT THE EVENING CONTINUING CONVECTIVE DEVELOPMENT. AS THE
WAVE CONTINUES TO EXIT ACROSS MN...THIS WILL FAVOR EASTWARD
PROPAGATION OF THE LINE THROUGH CENTRAL IA...STILL THE BROAD AREA
OF ISENTROPIC ASCENT SUPPORTS CONVECTION UPSTREAM FOR TRAINING
ACROSS THIS AREA AS WELL...KEEPING FLASH FLOOD THREAT POSSIBLE IN
THIS AREA AS WELL. 
 
GALLINA

ATTN...WFO...DMX...FSD...GID...OAX...

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

LAT...LON   43449485 43179338 42569356 41869486 40919666 
            41229763 41809766 42169757 42789712 43369616