US stocks Wednesday finished with modest gains as investors looked ahead to Thursday's congressional testimony by Federal Reserve Chair Janet Yellen. At the closing bell, the Dow Jones Industrial Average advanced 21.32 (0.13 percent) to 16,200.98. The broad-based S&P 500 finished essentially flat, up 0.09 of a point to 1,845.21, while the tech-rich Nasdaq Composite Index gained 4.48 (0.10 percent) to 4,292.06. Analysts said investors were looking ahead to Yellen's testimony at a Senate panel Thursday following a stream of mostly disappointing economic data that has been blamed in part on unusually cold weather. The S&P 500 again flirted with a new peak, but failed to close at fresh record. "We've seen a very powerful rally for the S&P 500," said David Levy, portfolio manager at Kenjol Capital Management. "What we're waiting for is a catalyst to drive the market higher." Levy said Wednesday data showing a big jump in new home sales, while positive, was already "priced in" to stocks.