MESOSCALE PRECIPITATION DISCUSSION 0547
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
715 PM EDT THU AUG 11 2016
 
AREAS AFFECTED...IOWA...EXT EASTERN NEBRASKA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 112315Z - 120515Z
 
SUMMARY...INCREASING CONVECTIVE ACTIVITY ACROSS IA...WITH TRAINING
AND EVENTUAL MERGERS WITH STRONG TRAILING COMPLEX IN E NEB LEADING
TO POSSIBLE FLASH FLOODING.

DISCUSSION...ELEVATED CONVECTION NORTH OF SURFACE WARM FRONT THAT
EXTENDS EAST FROM SURFACE WAVE NEAR KOFK BISECTING IA TO NEAR KDBQ
(AS A LIFTING OF OUTFLOW BOUNDARY FROM LAST NIGHT'S CONVECTION).
THE ELEVATED CONVECTION ACROSS N IA HAS GENERALLY WANED WITH
SLIGHTLY REDUCED SWLY LOW LEVEL UPGLIDE ACROSS THE BOUNDARY AND
GENERATED AN OUTFLOW BOUNDARY THAT IS NEARING INTERSECTION WITH
THE WARM FRONT PER DMX RADAR. THIS HAS LEAD TO A GENERAL
PERCOLATION OF TCU AND ISOLATED CBS BETWEEN THE BOUNDARIES WHICH
WILL CONTINUE TO EXPAND WITH TIME.  EXPECTATION IS FOR INCREASE AS
THE LLJ BECOMES NOCTURNALLY ACTIVE...YET SURFACE MST CONVERGENCE
ALONG THE BOUNDARY ALONG WITH AVAILABLE MLCAPES IN THE 3000-4000
J/KG RANGE PER THE RAP MAY SUPPORT VIGOROUS UPDRAFTS BEFORE LLJ
MAXIMIZES INFLOW LATER TOWARD 02-03Z.  ADDITIONALLY CONVECTION
ALONG THE WARM FRONT IN IA IS WITHIN HIGHLY DIVERGENT 500-1000MB
THICKNESS FIELD SUPPORTING SLACKENED PROPAGATION VECTORS WITH
GENERALLY 15-20KTS TOWARD THE ENE SUPPORTING OVERALL EWARD
TRAINING ALONG THE FRONTAL BOUNDARY.

GOES-E WV LOOP SHOWS A SHEARED WAVE LIFTING NE ACROSS NEB
PROVIDING BEST DPVA FOR ASCENT AS WELL LOCALLY BACKED LOW LEVEL
FLOW TO RAPIDLY DEVELOP LARGE CLUSTER OF CONVECTION ACROSS NE NEB
AT THIS TIME.  THIS IS ALSO SUPPORTED IN THE UPPER LEVELS WITH
MODERATE SPEED DIVERGENCE ON THE RIGHT ENTRANCE QUADRANT OF THE
80-90KT GENTLY ANTICYCLONIC 3H JET ACROSS NE SD AND MN.  TOPS TO
-77C AND BROAD UPDRAFT CORES SUPPORT A LARGE AREA OF HVY
RAINFALL...AND GIVEN LOW LEVEL BACKED FLOW...TPWS HAVE BEEN
POOLING INTO THE 2.0-2.25" RANGE...SUPPORTING HIGH RAIN RATES. 
THIS CLUSTER'S EVOLUTION ON THE FSD RADAR SUGGESTS SOME COLD POOL
GENERATION ALREADY AND INCREASED FORWARD PROPAGATION INTO IA ALONG
THE FRONTAL ZONE.  THIS WILL LEAD TO MERGERS WITH SLOWER MOVING
CONVECTION INCREASING SHORT TERM RATES AND INCREASING FLASH
FLOODING THREATS.  HI-RES CAMS LEAD BY THE LAST FEW RUNS OF THE
OPERATIONAL HRRR, HRRR PARALLEL AND WRF-ARW PAINT THE BEST SWATH
OF RAINFALL WITH GENERAL 3-4" TOTALS OVER THE NEXT 4-6HRS ALONG
THE LINE (HIGHER WEST WITH THE MORE EFFICIENT CLUSTER) WITH SOME
HINTS OF 5-6" POSSIBLE FROM RUN TO RUN WHICH SEEM PLAUSIBLE GIVEN
THE SETUP.  

WILL INCLUDE THREAT FOR QUICK/HIGH RATE FLASH FLOODING THREAT INTO
THE AREA OF CONCERN DUE TO CELLS THAT WILL CONTINUE TO DEVELOP
ALONG A SSW TO NNE PRE-FRONTAL PRESSURE TROF/SFC WIND CONVERGENCE
LINE ACROSS SE NEB INTO KS AS IT PROGRESSES INTO SW IA...WITH FF
GUIDANCE AND ANTECEDENT CONDITIONS A BIT MORE SUPPORTIVE OF
HANDLING THIS RAINFALL THE THREAT REMAINS MORE SCATTERED AND LESS
LIKELY FOR FF CONDITIONS TO OCCUR. 

GALLINA

ATTN...WFO...ARX...DMX...DVN...FSD...OAX...

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

LAT...LON   43209334 42899207 42379055 41679042 41579214 
            41019396 40639558 40659657 41449638 41979633 
            42849632 43169518