The S&P 500 would be poised for a strong advance if the index were able to really break through resistance at 2,400, technical analyst Katie Stockton told CNBC on Monday.
S&P 2,400 has kept a lid on the market since the index reached a record close of 2,395.96 on March 1, the chief technical analyst at BTIG said on "Squawk Box."
Last Monday, the S&P 500 closed above 2,400 for the first time ever. But at 2,402.32, that was not convincing enough to signal the start of a serious new spike higher, Stockton said.
The S&P has formed a "triangle pattern," she said, which "tends to be an interruption in the trend not a reversal of trend."