NEW YORK (TheStreet) -- U.S. stocks jumped on dovish comments from Federal Reserve Chair Janet Yellen. Trading is expected to be more volatile as investors close their first-quarter positions, a time when fund managers often sell their worst-performing stocks and buy the best-performing stocks to improve the appearance of portfolio statements. Global equity markets rose as Chinese and European Central Bank stimulus hopes persisted.

Yellen described the U.S. economy and labor market as far from healthy, suggesting the Fed's low interest rate policy will persist for some time. She told a conference the U.S. economy was "still considerably short" of the two goals assigned to the central bank: supporting low, stable inflation and maximum sustainable employment.

The Dow Jones Industrial Average added 0.82% to 16,457.66, while the S&P 500 rose 0.79% to 1,872.34. The Nasdaq closed up 1.04% to 4,198.99. Monday marked the end of the first quarter, and despite early struggles, the S&P 500 rebounded in March to post a quarterly gain of 1.3%. During the quarter, the Nasdaq added 0.54%, but the Dow lost 0.72%. 

  • China Premier Li Keqiang on Friday provided reassurances that the Chinese government has the required policies and steps laid out to provide the support needed for a cooling economy and would pursue infrastructure investment. As the European Central Bank gets ready for its monthly policy meeting on Thursday, speculation points to an easing of policy amid pressures that arose after reports showing a drop in inflation in Spain and Germany on Friday. Inflation in the eurozone slowed to a greater extent than expected in March to the lowest level in over four years. Consumer prices rose 0.5% following a 0.7% gain in February, spelling renewed pressure on the ECB to bolder the region's economic recovery.
  • International markets were mixed on Monday, with the Hong Kong Hang Seng settling up 0.39%, Japan's Nikkei 225 closing up 0.9%, the DAX in Germany shedding 0.33%, and the FTSE 100 in London off 0.26%.
  • Weekend talks between the U.S. and Russia failed to resolve the crisis in Ukraine, though both sides recoiled from escalating tensions any further.
  • In stock news, Cal-Maine Foods (CALM) - Get Report rose 9.2% after beating fiscal third-quarter earnings estimates by 36 cents at $1.77 a share amid improved volumes through the holiday season and higher average selling prices.
  • Panera Bread (PNRA) gained 1.4% after being raised to "outperform" from "neutral" by analysts at Wedbush.
  • Novartis (NVS) - Get Report popped 4.2% after the company announced that the trial of a chronic heart failure treatment is closing early based on the strength of interim results. Top gainers in the S&P included
  • Micron Technology (MU) - Get Report -- the stock closed up 8%; the company is expected to post a strong year over year rise in earnings when it reports this Thursday;
  • Biogen (BIIB) - Get Report and Delta Air Lines (DAL) - Get Report, shares of which gained 4% and 3.3% respectively;
  • Johnson & Johnson (JNJ) - Get Report, which added 0.81% after accepting an offer of about $4 billion from the private-equity firm Carlyle Group to buy its Ortho-Clinical Diagnostics business.

-- By Jane Searle, Andrea Tse and Joe Deaux in New York