Heavy rain Tuesday turned the chuckwagon racetrack into a muddy pool, leading to safety concerns. (CBC)

Heavy rain has forced the cancellation of the chuckwagon races and grandstand show at the Calgary Stampede for the first time in 85 years.

A major hailstorm on Monday became steady rain Tuesday, turning the racetrack into a muddy pool. Calgary was forecast to receive up to 20 millimetres of rain and winds gusting up to 80 km/h by the end of the night.

Due to safety concerns, Stampede organizers cancelled the GMC Rangeland Derby and the evening grandstand show, which features fireworks and live musical performances, on Tuesday night.

"The safety of our patrons, participants and animals is our first priority, and with the weather forecast calling for even more rain and wind, we feel it's imperative to cancel the chuckwagon races and the grandstand show," said Paul Rosenberg, vice-president of programming.

People with Tuesday night tickets can obtain full refunds in person at the Stampede, or via phone or online. Patrons can also try to rebook for a performance later in the week or for an evening show next year, said Stampede officials.

The rest of Stampede Park, including the midway, indoor shows and exhibitions, remained open.

The cancellation of the evening grandstand show was a blow to the Friends of the Young Canadians, who raise money for the singing and dancing performers by selling souvenir programs every night.

The Stampede chuckwagon races have been cancelled only once before on July 6, 1925, according to Billy Melville, archivist for the World Professional Chuckwagon Association.

With files from the CBC's Doug Dirks