The Dow Jones Industrial Average has surged 6 percent so far this year, and Thomas Lee, chief U.S. equity strategist for JPMorgan Chase, says the party can keep going for a long time.

He predicts to CNBC that the Dow may hit 20,000 within four years, and the Standard & Poor’s 500 Index 2,400 to 2,500.

That would represent a 44 percent gain for the Dow and as much as a 67 percent increase for the S&P 500.

Editor's Note: 'It’s Curtains for the US' — Hear Unapologetic Warning from Prophetic Economist.

Lee is impressed with the market’s ability to hit five-year highs, despite the reluctant participation of individual investors.

"There are a lot of reasons investors are sort of fighting the tape," he says. "There are still a lot of memories of '08 [the financial crisis]. We still have a taint on owning stocks."

However, crucial statistics argue for a continuation of the stock rally, Lee says. First, S&P 500 earnings now total about $100 a share. But, “the [historical] cycle peak in earnings is closer to $150.”

In addition, the price-earnings ratio for the S&P 500 is now 12.5 to 13, compared with the mid-cycle norm of 17, he says.

Other stock experts forecast more gains too. David Bianco, chief U.S. equity strategist for Deutsche Bank, lifted his forecast for the S&P 500 Friday by 25 points to 1,600 for this year.

And Dan Greenhaus, chief global strategist at BTIG Strategy, predicts 1,650, The Wall Street Journal reports.

Editor's Note: 'It’s Curtains for the US' — Hear Unapologetic Warning from Prophetic Economist.