WASHINGTON - A snowstorm Wednesday didn't keep Federal Reserve Chairman Ben S. Bernanke from outlining how the central bank might pull back its unprecedented intervention in the U.S. economy. In prepared testimony, Bernanke provided new details of how the Fed might scale back the steps it had taken to keep credit flowing without pushing the U.S. economy back into recession, including raising interest rates and reducing outstanding bank reserves. Although Bernanke talked a lot about what the Fed could do, he said little about when it might do it, using vague terms such as "in due course" and "at some point."