If it goes up, that's inflation and people will start thinking that the Federal Reserve will tighten money by eventually raising interest rates.
If it goes down, that's deflation and everyone gets very, very scared, since there's no way rates can go below zero, and Republicans in Congress get snarky if the Fed stimulates the economy in other ways.
Appropriately, Chicago Fed Pres. Charles Evans gives a speech at 11:15 a.m. He is the Lone Accommodationist (like the Lone Ranger but without the mask), who dissented in a November Federal Open Market Committee vote to maintain current policies, arguing that the Fed should do more to encourage growth.
A deflationary price index number would buttress his position.