Rain is in the forecast for the Indy 500 on Sunday, May 24, and it could arrive with thunderstorms. The National Weather Service is calling for a 30% chance of rain, mostly cloudy skies and a high around 81 degrees, while AccuWeather also puts the chance of rain at 30% and says a thunderstorm is possible.
For race fans, that is enough uncertainty to keep an eye on the sky. AccuWeather forecasters said rain can delay or cancel the race, and Weather Underground is more aggressive, showing a 60% chance of rain with precipitation starting at 12 a.m. and lasting most of the day, aside from a short dry window at 8 p.m. It also pegs the high around 75 degrees.
The difference in the forecasts is the story. One outlook leaves room for a mostly dry afternoon. Another suggests the track could be dealing with rain for nearly the entire day. In a sport where even a brief shower can change pit strategy, push back the start or force officials to wait it out, that spread matters as much as the percentage itself.
The weather is also shifting through the rest of Indianapolis 500 week. The National Weather Service says Carb Day on Friday, May 22, is likely to bring showers, with thunderstorms possible after 2 p.m. and a 90% chance of rain. Highs are expected in the low 70s. On Saturday, May 23, Legends Day is forecast to turn wet by mid-morning, with rain and thunderstorms lasting through the afternoon and possibly building again into the evening. Highs should reach near 78 degrees.
By Monday, May 25, the National Weather Service is predicting a 40% chance of rain for Memorial Day, with mostly cloudy skies and a high around 83 degrees. Weather Underground shows a similar 41% chance of rain and a high near 75 degrees.
That long view helps explain why every Race Day forecast draws attention. IndyStar analyzed 20 years of historic Weather Underground data for May 24 and found that it has rained only one day out of the last 20 May 24 race days since 2006. The average temperature over that stretch has been in the upper 60s, and even on rainy Indy 500 days, precipitation has usually been light, with the highest on record at just one-tenth of an inch.
The outlier remains May 30, 2004, when Race Day was inundated with nearly 4 inches of precipitation and the race eventually ran but was cut short because of a tornado in the area. That memory still hangs over every wet forecast, even when the numbers point to a lesser threat.
For now, the best answer to the weather tomorrow question is this: rain is possible, thunderstorms are possible, and the most likely outcome depends on which forecast holds up first. The next few days leading into Race Day should tell whether Indianapolis is headed for a damp delay or just another close call.
