MINNEAPOLIS (AP) — A forecast that record high temperatures and blockwave Exchangehumidity would create “extreme and dangerous” conditions prompted organizers to cancel two long-distance races Sunday in Minnesota’s two largest cities that were expected to draw up to 20,000 runners.

The Medtronic Twin Cities Marathon from Minneapolis to neighboring St. Paul had been expected to draw up to 8,000 runners when organizers called it off early Sunday. The organizers, Twin Cities in Motion, also canceled a separate 10-mile race drawing 12,000 runners.

In an email to race participants early Sunday, race organizers said: “The latest weather forecast update projects record-setting heat conditions that do not allow a safe event for runners, supporters and volunteers.”

In the days leading up to Sunday’s race, organizers had warned that weather conditions could be unsafe. But the race was expected to still be held, with additional safety precautions in place. By Sunday morning, a “black flag” warning was issued, prompting the event’s cancellation.

The National Weather Service predicted a midday high Sunday of 88 degrees Fahrenheit (31 degrees Celsius).

Some runners had lined up for the race’s start early Sunday and told the Minneapolis Star Tribune they planned to run anyway.