MESOSCALE PRECIPITATION DISCUSSION 0483
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1057 PM EDT MON SEP 07 2015
 
AREAS AFFECTED...VICINITY OF THE NE/MO/KS/IA BORDER JUNCTION 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 080256Z - 080856Z
 
SUMMARY...THUNDERSTORMS ACROSS SOUTHEAST NE ARE EXPECTED TO EXPAND
EAST TO EAST-SOUTHEAST WITH TIME. FLASH FLOODING IS POSSIBLE
WITHIN A REGION OF SATURATED SOILS.

DISCUSSION...AN EXPANDING AREA OF SCATTERED THUNDERSTORMS ACROSS
SOUTHEAST NE IS BEING CAUSED BY AN INCREASE IN LOW-LEVEL INFLOW
OVER THE TOP OF A WEAK THERMAL BOUNDARY.  PRECIPITABLE WATER
VALUES IN THE AREA ARE ~1.75", 2.5 SIGMAS ABOVE THE MEAN FOR EARLY
SEPTEMBER.  A SHORTWAVE MOVING IN INTO THE AREA FROM THE NORTHWEST
ALONG WITH A JET STREAK INVADING FROM CO APPEAR TO BE THE CULPRITS
IN THUNDERSTORM FORMATION.  INFLOW AT 850 HPA IS 25-40 KTS PER
RECENT VAD WIND PROFILES OUT OF THE SOUTH-SOUTHWEST, ABOVE THE
MEAN 850-400 HPA WIND FLOW.  THIS INFLOW IS IMPORTING MUCAPES OF
2000+ J/KG.

AS LOW-LEVEL INFLOW AND EXPANDS EASTWARD, THE THUNDERSTORM AREA
SHOULD FOLLOW SUIT.  AS THE LOW-LEVEL INFLOW INCREASES, THERE IS
THE POTENTIAL FOR BACKBUILDING.  OTHERWISE, THERE IS A BIT OF
DIRECTIONAL WIND SHEAR IN THE REGION, WHICH SHOULD FORCE FORWARD
PROPAGATION TO THE EAST TO EAST-SOUTHEAST AT 35 KTS PER FORWARD
PROPAGATING CONVECTIVE VECTORS; CELL MERGERS AND TRAINING ARE
CONSIDERED THE MAIN HEAVY RAIN THREAT.  THERE ARE TWO CONDUITS
AVAILABLE TO HELP FOCUS CONVECTION: THE MAIN FRONTAL BOUNDARY
ACROSS IA AND THE MESOSCALE BOUNDARY IN NORTHEAST KS.  THE
MESOSCALE QPF GUIDANCE IS IN FAIRLY GOOD AGREEMENT, IN ADVERTISING
LOCAL AMOUNTS IN THE 3-5" RANGE THROUGH 09Z.  THIS RAIN COULD FALL
QUICKLY, AS AVAILABLE MOISTURE SUPPORTS HOURLY RAIN RATES UP TO
2".  BELIEVE THE NON-HRRR GUIDANCE HAS A GOOD HANDLE ON THE QPF
PLACEMENT DURING THIS TIME FRAME FROM THIS CONVECTIVE AREA; WILL
EXPLORE SHORTLY WHETHER OR NOT CONVECTION FROM SOUTHERN SD COULD
HAVE A SIMILAR IMPACT IN AREAS FARTHER NORTH ACROSS IA.  FLASH
FLOODING IS POSSIBLE OVER AN AREA OF RECENTLY SATURATED SOILS.

ROTH

ATTN...WFO...DMX...EAX...GID...OAX...TOP...

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

LAT...LON   41649482 41089279 39349313 40109577 40229840 
            41059756