Retail sales finally blossomed in April, but scratch the surface and those impressive gains are only skin deep.

Up against the easiest comparisons of the year so far and benefiting from both the early Easter shift and warmer weather, same-store sales posted the biggest monthly gains since November 2007.

But investors weren't overwhelmed and remain cautious that an upturn is on the horizon for what has been a tough retail season so far. The S&P Retail Index fell 1.9 percent to 395.16, while the WWD Composite Index dropped 0.6 percent to 911.37. The Dow Jones Industrial Average was up 0.4 percent to 12,866.78 and the broader S&P 500 rose 0.4 percent to close at 1,397.68.

"If you look at March and April together, as we have been trained to do, results were not that impressive and really only mediocre," said Eric Beder, retail analyst at Brean Murray, Carret & Co.

Combining March and April provides investors with a more accurate picture of comp trends given the calendar shift.

Same-store sales in April were also cosmetically altered by retailers who "bought" their numbers with increased promotions and markdowns, said Christine Chen, retail analyst at Needham & Co.

Despite April's numbers and the presumed benefit of tax-rebate checks, both retailers and analysts predict it is still a bumpy road ahead.

"We are looking for modest improvement in May and June comp-store sales buoyed by rebate checks," said Ken Perkins, research analyst at Retail Metrics Inc. "The impact of the stimulus will likely be muted somewhat by the continuous upward drumbeat of higher prices at both the [gas] pump and grocery stores."

Upwardly revised earnings guidance by a number of companies will hopefully stem the free fall in first-quarter retail earnings estimates, he continued. A slew of major retailers report their first-quarter numbers next week, including Wal-Mart Stores Inc., Macy's Inc., J.C. Penney Co. Inc. and Nordstrom Inc.

Across the board consumers were looking for bargains last month, making the discount sector the standout winner in terms of comps. Of the retailers tracked by WWD, the mass merchant sector posted an average gain of 7.1 percent, while the specialty sector increased 3.9 percent. The department store channel rose a modest 1.1 percent.