BY TOM O'NEILL
The Cincinnati Enquirer
An unusual weather pattern at about 25,000 feet above the Louisville area directed the path of the rainstorm that devasted some Southern Ohio counties and Northern Kentucky.
Cincinnati was largely spared for one simple reason: luck.
''We knew it was going to rain, but what surprised us was the amount,'' meteorologist Steve Wilkinson of the National Weather Service in Wilmington, Ohio, said Sunday. ''Cincinnati was north of where it happened, just lucky, but there will be backwater flooding there.''
Cincinnati received .94 inch Friday night, 1.39 inches Saturday and none Sunday, Mr. Wilkinson said.
By contrast, areas of Brown and Adams counties, about an hour's drive from Cincinnati, got an estimated 8 to 10 inches of rain, causing at least two deaths and prompting mass evacuations.
The thunderstorm system combined with tornadoes to devastate parts of Little Rock, Ark., where 24 deaths were reported. It continued a northern path along the Ohio River in southwestern Kentucky, dumping 4ï inches on Paducah and 10.24 inches on Louisville.
But instead of continuing along the Ohio River up to Cincinnati, the storm moved inland, cutting a swath through north-central and Northern Kentucky. In southeastern Arkansas and northwestern Mississippi, converging systems caused several tornadoes in those states as a warm front from the Gulf of Mexico traveled north.
A second development, directly affecting Cincinnati, occurred north of Louisville, Mr. Wilkinson said.
Normally with a low pressure system, rain tapers off as the warm front moves north. This weekend, however, a diffluence appeared at about 25,000 feet above Louisville, which pushed the storm northeast, setting its path south of Cincinnati.
A diffluence occurs when high-atmosphere winds are blowing away from each other. When there is high moisture air below it, the combination causes a sharp increase in precipitation, Mr. Wilkinson said.
''This event isn't unusual by themselves but with everything coming together, it can be very dangerous,'' he said.