Like the thesis statement, (or thesis sentence or topic sentence), a forecasting statement gives your reader an initial sense of a essay's meaning and organization. A forecasting statement previews what lies ahead. It is an effective way to tell your reader in advance about the organization of your composition.
You should provide enough detail so that your reader knows something
specific about the arrangement of the essay that follows. For instance,
in the basic five-paragraph essay it is customary to develop three points in
the three supporting paragraphs. These three points should be stated
specifically in the forecasting statement.