Janet Yellen is preparing to walk a tightrope.

When the Federal Reserve chair addresses lawmakers this week in Washington, she will have to strike a balance between sounding confident on the domestic economy and acknowledging increased risks from abroad. Two weeks after officials signaled interest rates may rise more slowly than previously expected, economists and investors will be trying to gauge Yellen's willingness to delay tightening at the March meeting.

With financial market-turmoil causing uncertainty about the outlook, energy prices damping inflation and the European Central Bank preparing a stimulus boost that may bolster the dollar, the market-implied probability for a rate increase next month has dropped to 10 percent from more than 50 percent at the start of the year. Policy makers including Vice Chairman Stanley Fischer have cautioned that it's still too soon to decide the next step.