Forewarnings are the dramatic indicators that the story consequence is closing in and the goal is more in peril.  In a given story structure, all the forewarnings will pertain to the same kind of thing, such as cracks forming in a dam.

In some structures, forewarnings pertain to the past:

For example, discovering that the inhabitants of a stone age village that is being excavated died of a mysterious virus; finding love letters written by your spouse before you were married that are addressed to one of your friends with whom your spouse is currently working on a business project; seeing pictures of yourself in a hidden family album that lists you by a different name; learning that, historically, all the women in a family have died of breast cancer, etc.

From the Dramatica Software