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."
Stockton predicted some possible near-term selling with support at 2,340, but argued "momentum is still quite strong."
If the S&P were to blow past 2,400, Stockton said the index could then soar 10 percent to 2,460, she predicted. The S&P closed at 2,381.73 on Friday.
"The 2,640 level is really assuming the same trajectory as the current trend, which is pretty steep when you go back to the November lows," she said.
The S&P 500 has gained 11.3 percent since won the 2016 presidential election in November.
Addressing concerns about the Trump rally, Stockton said, "The breadth is actually quite strong behind the market ... most stocks have participated in the uptrend."
Last July, Stockton predicted on CNBC that the S&P would make a move to 2,400. The index was trading around 2,135 at the time.