MESOSCALE PRECIPITATION DISCUSSION 0140
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
926 AM EDT THU JUN 19 2014
 
AREAS AFFECTED...SOUTHERN MN/NORTHERN IA/SOUTHWEST WI 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 191326Z - 191926Z
 
SUMMARY...FLASH FLOODING WILL BECOME INCREASINGLY LIKELY ACROSS
THE MOST SUSCEPTIBLE AREAS AS CONVECTION ACCOMPANIED BY HIGH
RAINFALL RATES EXPANDS.

DISCUSSION...CURRENT ANALYSIS AND OBSERVATIONAL TRENDS INDICATE
GREATER COVERAGE AND PERSISTENCE OF CONVECTION OCCURRING NORTH OF
A STATIONARY FRONT DRAPED ACROSS CENTRAL IOWA...FFG VALUES
CONTINUE TO LOWER IN RESPONSE TO ANTECEDENT AND ONGOING RAINFALL. 
THESE TRENDS ARE ON CONTRAST THE MAJORITY OF HIGH RESOLUTION
NUMERICAL GUIDANCE THAT SUGGESTS CONVECTION SHOULD BE WANING. 
HELPING TO SUSTAIN CONVECTION IS ENHANCED STORM RELATIVE
CONVERGENCE AND ASCENT CREATED BY THE NORTHEASTERLY FLOW NORTH OF
THE FRONT AND MODERATE SOUTHWESTERLY FLOW ASCENDING THE SLOPING
FRONT. 

CONVECTION IS ALSO EXPANDING WITHIN THE WARM SECTOR SOUTH OF THE
FRONT INCLUDING MUCH OF SOUTHWEST IOWA...SUPPORTED BY NEARLY
SATURATED SURFACE TO 700 MB MOISTURE ADVECTION AND NEARLY ZERO CIN
WHICH IS EVIDENT BY RADAR TRENDS AND THE 12Z KTOP RAOB...AND
DEPICTED AT THE SURFACE AS A WAVE OF LOW PRESSURE OVER SOUTHEAST
NEBRASKA.   

FINALLY...THERE IS CONSIDERABLE DISPARITY BETWEEN WSR-88D AND DUAL
POL RAINFALL ESTIMATES...WITH THE DUAL POL ESTIMATES AS MUCH AS 50
TO 100 PERCENT HIGHER. GAGE OBSERVATIONS ARE TOO SPARSE AT THE
MOMENT TO DETERMINE WHICH ESTIMATES ARE MORE CORRECT.  ASSUMING
THAT BOTH TECHNIQUES ARE SOMEWHAT CORRECT...COARSE ESTIMATES OF
HOURLY RAINFALL RATES OF 0.5 TO 1.5 ARE LIKELY TO CONTINUE...WHICH
ARE LIKELY TO EXACERBATE EXISTING FLOODING PROBLEMS.

JAMES 

ATTN...WFO...MKX...DVN...ARX...MPX...DMX...FSD...

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

LAT...LON   42528996 43899087 44899290 44859456 44109531 43269527
            42369441 41699297 41529103 42528996