Early-warning signal

Name the observable indicator that tells you the floor is being approached while you still have room to act. It has to be something you can actually see or measure in the moment, not a conclusion you reach afterward.

Name the observable indicator that tells you the floor is being approached while you still have room to act. It has to be something you can actually see or measure in the moment, not a conclusion you reach afterward.

Example

On the hike: less than 90 minutes of daylight margin left, or the slowest member needing rest stops more than twice an hour. Either one is visible on the trail, and either one fires well before the group is stuck above treeline in the dark.