MESOSCALE PRECIPITATION DISCUSSION 0692
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
203 AM EDT FRI SEP 23 2016
 
AREAS AFFECTED...PORTIONS OF NORTHERN IA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 230602Z - 230902Z
 
SUMMARY...DISORGANIZED THUNDERSTORMS CONTINUE TO SHOW SOME CELL
TRAINING CHARACTER OVER AREAS WITH SATURATING SOILS.  FLASH
FLOODING REMAINS POSSIBLE.

DISCUSSION...A QUASI-STATIONARY FRONT HAS SAGGED SLIGHTLY
SOUTHWARD OVERNIGHT DUE TO EARLIER CONVECTION IN SOUTHERN IA.  AS
INSTABILITY HAS LESSENED DOWN THERE, CONVECTION IS BECOMING A
LITTLE MORE CONCENTRATED IN NORTHERN IA NEAR THE 850 HPA PORTION
OF THE FRONTAL ZONE.  PRECIPITABLE WATER VALUES OF 1.8-1.9" REMAIN
ACROSS THE REGION, AND INFLOW AT 850 HPA OF 20-30 KTS IS
OVERRIDING THE SURFACE BOUNDARY, NEARLY DOUBLE THE MEAN 850-400
HPA WIND, WHICH IS AIDING PRECIPITATION EFFICIENCY.  INSTABILITY
ACROSS NORTHERN AND SOUTHWEST IA HAS BARELY BUDGED FOR THE LAST
SEVERAL HOURS, REMAINING ABOVE 1000 J/KG.

OVER THE NEXT SEVERAL HOURS, LOW-LEVEL INFLOW AND MUCAPES IN THE
REGION ARE EXPECTED/FORECAST TO DEGRADE, WHICH SHOULD EVENTUALLY
END THE FLASH FLOOD EPISODE.  SLIGHT NORTHWARD MOVEMENT IN THE 850
HPA BOUNDARY IS ALSO FORECAST.  RECENT RAP-BASED MASS FIELDS
INDICATE MUCAPES DROPPING UNDER 1000 J/KG BY 09Z AND INFLOW
SLACKENING BY 11Z.  GFS-BASED GALVEZ-DAVISON INDEX VALUES FROM ITS
18Z AND 00Z RUNS IMPLY DECLINING CONVECTIVE COVERAGE/ POTENTIAL
WITH TIME OVERNIGHT.  HOURLY RAIN RATES OF UP TO 2" WITH LOCAL
AMOUNTS IN THE 2-4" RANGE COULD LEAD TO OR CONTINUE FLASH FLOODING
OVER AREAS WITH SATURATING/SATURATED SOILS.

ROTH

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

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

LAT...LON   43419380 43189167 42299088 41929137 41869231 
            42209432 42769533 43209487