MESOSCALE PRECIPITATION DISCUSSION 0330
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
301 AM EDT THU AUG 28 2014
 
AREAS AFFECTED...ERN NE...WRN IA...FAR SE SD...FAR NW MO 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 280700Z - 281200Z
 
SUMMARY...MODELS SIGNAL THE INTENSIFICATION OF ORGANIZED HEAVY
RAIN THROUGH EARLY MORNING OVER EASTERN NE AND WESTERN IA. SOME
LOCATIONS WILL RECEIVE 2 INCHES OF RAIN IN A SHORT TIME DURING THE
ONSET. ISOLATED STORM TOTALS OF GREATER THAN 4 INCHES ARE
POSSIBLE...AND FLASH FLOODING IS LIKELY.

DISCUSSION...THE 00Z HIRES MODELS AND SEVERAL HRRR RUNS PREDICT
ESCALATION OF THE COVERAGE OF HEAVY RAIN...AND ITS LONGEVITY OVER
A GIVEN POINT...DURING THE EARLY MORNING HOURS. THIS APPEARS TO
OCCUR AS THE UPPER AIR PATTERN AMPLIFIES WITH A TROUGH PULLING
PAST THE ROCKIES FRONT RANGE. THIS PLACES A DIVERGENCE MAXIMUM IN
SYNC WITH A PRE-EXISTING MCV PER RADAR LOOPS...AND A STRONG LOW
LEVEL JET IN EASTERN NEBRASKA. THIS SETUP...ALONG WITH SUFFICIENT
CAPE AND UNUSUALLY DEEP/RICH MOISTURE...WILL SUPPORT UPSCALE
GROWTH OF CONVECTION PRODUCING VERY EFFICIENT RAINFALL...AT LEAST
2 INCHES PER HOUR WHEREVER TRAINING OCCURS.

ALTHOUGH STRONG WIND FIELDS WILL YIELD QUICK MOTION FOR INDIVIDUAL
CELLS AND THE MCV...THE MODELS PREDICT AN INCREASE OF WEST TO EAST
TRAINING AS THE MCV SETTLES ONTO THE NOSE OF ENHANCED 700 MB
SOUTHERLY FLOW. THIS MAY OCCUR WITHIN 50 MILES NORTH OR SOUTH OF
THE LATITUDE OF OMAHA NE...AND EXTENDING BOTH WEST AND EAST OF THE
NE/IA BORDER. THE 00Z NAM CONEST AND 00Z NSSL WRF PRODUCE
PARTICULARLY HEAVY SWATHS OF RAIN AT THAT LATITUDE...WHILE OTHER
MODELS PLACE THE RAINFALL AXIS FARTHER SOUTH AND NEARER TO THE
CAPE AXIS. OTHER POCKETS OF HEAVY RAIN WILL LIKELY OCCUR AROUND
THE PERIPHERY OF THE MORE ORGANIZED MCS...AS LARGE SCALE
ADVECTIONS AND HEIGHT FALLS PLAY UPON THIS MOISTURE RICH
ENVIRONMENT...IN WHICH PRE-CONVECTIVE PW VALUES ARE JUST UNDER 2
INCHES...OR 2.5 STANDARD DEVIATIONS FROM CLIMATOLOGY. ONE AND
THREE HOUR FLASH FLOOD GUIDANCE IN THIS REGION IS AS LOW AS 1 TO
1.5 INCHES...A FURTHER INDICATION THAT FLASH FLOODING IS LIKELY.

BURKE

ATTN...WFO...DMX...EAX...FSD...OAX...GID...LBF...

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

LAT...LON   43649526 43159456 41919401 40319483 40029757 40379962
            41599973 43499704 43649526