Tom Lee: S&P could be up double digits this year

The market's message
The market's message

Despite soft a first-quarter GDP, longtime bull Tom Lee still sees room to run for the .

Lee, co-founder of equity research firm Fundstrat Global Advisors, told CNBC's "Squawk on the Street" on Monday that he's looking at the correlation between high-yield bonds and the stock market.

"The year after high yield has a negative return year, which is 2015, the S&P's almost always up double digits," Lee said.

"I'll dismiss people who say the stock market's expensive because bull markets peak at 25 times. We're roughly 15 times forward. So, I wouldn't say it's out of the question to say the S&P's up double digits this year," he said.

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Scott Brown, chief economist at Raymond James, is also positive on the stock market. For investors who point to weak data points as a reason to stay conservative, Brown said that in the last six years the United States has seen a rebound after a soft first quarter. That being said, Brown isn't as bullish as Lee.

"Early indications are we'll see a pickup in growth in the second quarter and beyond, but it may not be especially strong," Brown said Monday on "Squawk on the Street."

"When you look at the market in the first part of the year, it was really dominated by fear for the first six weeks or so, fear of recession, fear of a weak global economy, fear of the Fed. A lot of those fears have subsided, but not necessarily gone away completely," he said.

Is the S&P 72% overvalued?
Is the S&P 72% overvalued?