Pop Quiz: When is it too late to cancel a class?

See my post about Monday August 11 to understand where the content for this quiz is coming from.

So I am not going to beat around the bush. A natural disaster happened on the way to work the other day and I did not cancel class because it happened so fast and I was in the middle of it I could not. However, there are times when a school does not close (like the other day) and the weather prompts you to think should I cancel class?

What do you think? Does it make sense to cancel class half-way through a commute when you know other students are on their way? Should you cancel a class due to weather when the school does not close? 

Featured image: Auditorium