The race has always been scheduled in conjunction with Memorial Day. Through 1970, the race was held on Memorial Day proper (May 30), regardless of the day of the week, unless it fell on Sunday. In those cases it was scheduled for Monday May 31. After the Uniform Monday Holiday Act took effect in 1971, the race was scheduled as part of the three-day Memorial Day weekend instead, either the Saturday, the Sunday, or the Monday. Since 1974, the race has been scheduled for the Sunday of Memorial Day weekend, and has been held on Sunday with only two exceptions due to rain delays.

What's the best answer to this question: has the indy 500 ever been rained out?
yes