MESOSCALE PRECIPITATION DISCUSSION 0470
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
752 PM EDT THU AUG 27 2015
 
AREAS AFFECTED...NORTHEAST NEBRASKA....NORTHWEST IOWA...SOUTHEAST
SOUTH DAKOTA...SOUTHWEST MINNESOTA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 272339Z - 280539Z
 
...CORRECTED TO ADD SUMMARY...

SUMMARY...FOCUSED FLASH FLOODING POTENTIAL AS SHARPLY DEFINED
SHORTWAVE ENHANCES LLJ CYCLE THIS EVENING.

DISCUSSION...IN COORDINATION WITH NESDIS SAB...PLEASE REFER TO
SPENES ISSUED AT 2229Z DESCRIBING THE SYNOPTIC SETUP FOR FOCUSED
FLASH FLOODING THREAT THAT WILL BE INCREASING THIS EVENING ACROSS
THE MID MISSOURI RIVER VALLEY.  

SHORTWAVE LIFTING NORTHEAST ACROSS CENTRAL NEBRASKA IS PRODUCING
GOOD PVA AND HEIGHT FALLS ACROSS EASTERN NEBRASKA...INCREASING
ASCENT AND STRENGTHENING LOW LEVEL FLOW THAT IS MAXIMIZING 850MB
MOISTURE FLUX TOWARD WARM FRONT DRAPED ACROSS THE AREA. INITIALLY
ELEVATED CONVECTION OVER NEBRASKA WILL ONLY SET THE STAGE FOR THE
INCREASING CONVECTIVE ACTIVITY AT NIGHTFALL.  AT THE SAME TIME
BINARY INTERACTION WITH UPSTREAM VORTICITY FEATURE OVER SOUTH
DAKOTA SHOULD HELP SLOW AND POTENTIAL PIVOT THE LEAD SHORTWAVE
NORTHWESTWARD INTO DIVERGENT 7H FLOW...ALLOWING FOR A ZONE OF
DEFORMATION TO HELP NARROWLY FOCUS THE LINE OF CONVECTION ACROSS
NORTHEAST NEBRASKA INTO NW IOWA.  THE OVERNIGHT ENVIRONMENT WILL
BE MARKED BY DECENT REMAINING INSTABILITY AND LLJ IN EXCESS OF
50KTS WITH MODERATE MOISTURE...TPWS INCREASING TO 1.75". THE
DEVELOPING MCS SHOULD SUPPORT RATES OF 1.5-2"/HR AND TOTALS OF
2-4" LIKELY WITH POSSIBLE HIGHER TOTALS OCCURRING IN MERGERS.
THERE IS FAIRLY GOOD AGREEMENT TOWARD THIS SCENARIO WITHIN THE
HI-RESOLUTION CONVECTION ALLOWING MODEL SUITE...WITH WPC
PARTICULARLY FAVORING THE 18Z GEM-REGIONAL AND NSSLWRF AND RECENT
ESRL EXPERIMENTAL HRRR RUNS. 

AN ADDITIONAL ELEVATED BAND OF ENHANCED SHOWERS AND THUNDERSTORMS
ORIENTED UNDER THE UPPER-LEVEL SHORTWAVE RIDGING (SEE WV LOOP)
ACROSS SE SD INTO SW MN SHOULD BE DEVELOPING AROUND 02-04Z. WITH
SOME REDUCED FLUX DUE TO UPSTREAM CONVECTION THE SAME MODELS
APPEAR TO HAVE GOOD ORIENTATION TO QPF BUT MAY BE OVERDOING THE
TOTALS A SHADE...THINKING A MORE SCATTERED 1-2" WITH ISOLATED
HIGHER AMOUNTS POSSIBLE. 

GALLINA

ATTN...WFO...DMX...FSD...LBF...OAX...

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

LAT...LON   44269727 43259423 41849440 41189609 41549770 
            41949871 42659931 43499912