The agency says there's a possibility of scattered showers and thunderstorms after 2 p.m. Sunday, with a high near 88.
The most recent of 14 rain delays or postponements was in 2007, when the race was halted after 415 miles. In 2004, the race was delayed two hours by rain, stopped after 27 laps, restarted after another delay of almost two hours and stopped for good after 450 miles.
There was a record 3.8 inches of rain on race day in 2004.
The hottest Indy 500 was 92 degrees in 1937; the coldest was a high of 58 in 1992.