By many popular measures, the dollar has traded sideways for the last six months. Then there's the Federal Reserve's measure.

The greenback is surging, according to an index the Fed created to track the U.S. currency versus 26 of the country's biggest trading partners. It's risen 1.3 percent beyond a 12-year high reached in March, when the central bank fired the first of a series of warnings that a stronger dollar may hurt growth and lower inflation. 

At a time when the Fed's tightening path has become one of the biggest drivers in the $5.3 trillion-a-day foreign-exchange market, the discrepancy between Wall Street's view -- largely based on the dollar's performance against the euro and the yen -- and that of policy makers may lead to a jolt for investors expecting recent ranges to persist. The rapid trade-weighted appreciation this quarter has come mostly against big exporters such as China and Mexico, and it undercuts the Fed's goal of quicker inflation. It may trigger further jawboning from officials looking to cool the dollar's broad gains as the Fed begins raising interest rates for the first time in almost a decade. 

``The dollar still continues to strengthen on a trade-weighted basis and the Fed definitely takes that into the equation,'' said Brad Bechtel, a managing director at Jefferies Group LLC in New York. ``The risk is the Fed starts really emphasizing that, and the market would be caught offside.''