S&P 500 headed for a Friday fall with futures down 26 points

1. Uncertainty reigns

If non-farm payrolls was worse, you'd have traders buying stocks expecting a dovish Fed. Or if it was stronger but with weak wage growth, you'd have a different reason to buy. Overall, no one really knows what the Fed is thinking or what's happening with China so the safest place is the sideline.

2. Long weekend

The best way to ruin your weekend is to put on a big trade on Friday. That's even more true ahead of a long weekend.

3. China returns Monday

Chinese markets have been closed since Wednesday and reopen Monday. A main driver is Chinese stock market sentiment at the moment and US traders won't get a crack until after two full days of Chinese trade. Given the volatility in that market, it's another reason to pare risk.