On August 21, 2014 several meteorological variables came together across East Central Indiana leading to flash flooding of historic proportions, which many are calling a "1 in 100 year" event.
That morning, a slow-moving frontal boundary began lifting north out of the Ohio Valley, with dewpoints soring into the low 70s behind the front. At the same time, an advancing ridge of high pressure began to build east across the Midwest from the Central Plains. The ridge also aided in baroclinic lift, with showers and thunderstorms training along the periphery of the surface high.
Showers and heavy thunderstorms began impacting the region shortly after daybreak, as the first of a series of mid-level impulses rounded the ridge axis. These impulses - referred to as vort max's by Meteorologists, promote enhanced lift downstream of the direction wind is coming from. As air enters one of these impulses, it is accelerated by ageostrophic components.
By Noon, the front had lifted far enough north and east for ongoing convection to spread across Central Ohio. Breaks in cloud cover aided in daytime heating and atmospheric instability across East Central Indiana. By the mid-afternoon hours, most of the area lied within the warm sector, with surface dewpoints well in the 70s.
The front then began to slowly drift south, as another series of mid-level impulses moved southeast from Wisconsin. By dark, the front had become nearly stationary, with showers and severe thunderstorms impacting Northern Illinois and Northwest Indiana.
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12-hour NEXRAD loop from August 22, shows showers and heavy thunderstorms training along a stationary front across Central Indiana (image courtesy of NEXLAB - College of Dupage and UCAR).
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By Midnight, a slow-moving MCC - or Mesoscale Convective Complex, had formed across North Central Indiana. As this complex moved southeast, additional showers and thunderstorms exploded along the stalled front, ahead of a very moist and unstable air mass.
With little steering winds aloft, storm movement was very slow. Heavy rain - in upwards of an inch an hour, inundated portions of East Central Indiana. Particulary hardest hit was Hartford City in Blackford County, which lied directly in the path of an elongated vort max. By daybreak, as much as 11 inches of rain had fallen within a 12-hour window.
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48-hour precipitation totals show a corridor of dark red, indicating as much as 10 inches or more of rain fell along a Marion to Muncie line, much of which occurred within a 12-hour window (image courtesy of the National Weather Service).
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Climatologically, the atmospheric variables that came together on August 22, 2014 to produce historic flash flooding across East Central Indiana were a 1 in 50-100 year event.
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Afternoon storms in the Central Plains should be minimal, but not ruled out, with the main threat for storms starting along a cold front later in the day. Dew points reaching the mid-upper 60s by late afternoon, deep vertical shear, steep lapse rates, high cape values, westerly flow aloft, and a moist southerly flow bringing in tropical moisture from the gulf, creates the perfect environment for severe storm development. Isolated supercells should begin the storm development along the cold front that will be making its way through the area later today. Later in the evening storms should start to grow and develop into bowing segments capable of producing damaging winds and large hail. Expect to see a few isolated tornados and some very heavy rain with these storms as well.
