The usual increase in volatility and volume that typically comes along with quadruple witching—the last trading day for stock options on indexes, equities and futures, with futures themselves also expiring—on Friday will be accompanied by the S&P 500's quarterly rebalancing.
"All our way of helping the triple-witching hour day," said Howard Silverblatt, senior index analyst at the S&P Dow Jones Indices, of the rebalancing that will have Facebook joining the S&P 500 and three other issues getting the boot.
"The only guarantee at the end-of-the-year expiration is a lot of volume. You can't read too much in terms of direction; we're going to get a lot of volume, that's all I can predict," said Peter Boockvar, chief market analyst at The Lindsey Group.
"There is usually some volatility right at the opening, and then throughout the day because of the rebalancing, and as we head into the last hour, there will be a lot of order inbalances, one way or the other," said JJ Kinahan, chief strategist at TD Ameritrade.
Major U.S. Indexes
"New stocks come in, old stocks go out, Facebook is probably the one people care about," said Kinahan added of the companies being added by Standard & Poor's to the S&P 500 Index after the close of business on Friday.
In addition to the social media company, floor coverings products maker Mohawk Industries is joining the S&P 500, while Abercrobie & Fitch, JDS Uniphase and Teradyne are getting ousted, with the trio headed to the S&P MidCap400.
"There's a lot of quarterly rebalancing going on, and some people are attributing yesterday's move to it," added Bockvar of the rally that followed the Federal Reserve's decision to start cutting stimulus.
—By CNBC's Kate Gibson