Fed Chair Janet Yellen could clear the air next week, sounding more concrete on whether the central bank will squeeze in a rate hike or two this year, but more likely she won't.

Yellen is scheduled to speak next Friday in Jackson Hole, Wyoming, and for markets that has been the most important event on the calendar this month. It also comes after the debate in markets heated up about whether the Fed could actually raise rates in September, or will wait until the end of the year or even later.