"We can already feel right now how activity's shutting down for the weekend. It feels like they pulled the plug on the market momentum," said Bank of Tokyo-Mitsubishi chief financial economist Chris Rupkey.
Trading volumes are expected to be sluggish on Friday, and desks should still be relatively lightly staffed, but they will be primed for Yellen's 1 p.m. ET speech on the economy to the Greater Providence Chamber of Commerce. The consumer price index is released at 8:30 a.m. ET, and is expected to show a 0.1 percent gain on the headline, or 0.2 percent, without food or energy.