Down here, a lot of time it isn’t so much that the RD wants to cancel or modify a race at the last minute. It’s that as a condition of getting a permit, he has to agree to let the sheriff’s department, National Park Service, Department of Defense, etc. revoke the permit, even at the last minute, if the group issuing the permit feels like conditions are unsafe or otherwise inappropriate.
As long as the sheriff’s department gives it a go, people will pretty much race in anything down here, including posted Tropical Storm Warnings (‘Hey, we’ll get the race in before the bad feeder bands make shore, and just tell everyone to call the bike shop on Monday for results…’) though course modifications are relatively common.
The only out and out cancellation within a few days of the race I can remember was Santa Rosa Island in 2004 because of Hurricane Ivan, and that was because the swim course was too hazardous to use because too many peoples’ homes had washd into the Gulf, the bike and run courses were under four feet of sand, and the National Guard wasn’t letting anyone on the island anyways.
And then people were apparently tracking down the temporarily homeless RDs’ cell phone number and bitching about getting full refunds.