The USD's most important risk factor are tapering concerns.

If QE remains then you should see BTC going back up with a weaker dollar.
Also vice versa, lower bitcoins with more faith in the dollar.

Start thinking about the bigger picture when you want to play cryptocurrencies.
If the Eurozone of US show signs of weakness in their currency, albeit anything really -- btc's value will go up.

A good way to keep track of US dollar's trend is by looking at the Dollar Index vs. 6 major currencies.