U.S. stocks gather steam; Europe closes mixed By: CNBC.com News February 27, 2014 at 11:58 AM EST Stocks turn positive, reversing early losses. Fed Chair Janet Yellen says harsh winter weather has played a role in recently weak economic data. Read More >> Related Stocks: Best Buy Chico's Fas Emrg Mkts Ishares MSCI ETF First Solar J C Penney Company Inc Sentinelone Inc Cl A