This one chart signals a bear market may be here

Louise Yamada, who spent 25 years as the top technical analyst for Citigroup and now runs her own firm, believes stocks are not out of the woods and remain vulnerable to a large drop.

In the past two years, equities have been contained in a trading range, moving sideways as momentum faded, Yamada said, explaining that the combination of those factors has not been a positive sign for stocks in the past.

In May 2015, the chart analyst alerted clients to a long-term momentum sell signal, which has not reversed despite the temporary rallies the market has experienced. "That leaves us a little suspect as to how this is going to pan out," Yamada said, emphasizing the potential for a bear market.

In this extensive strategy session about technical analysis hosted by CNBC's Mike Santoli earlier this week, Yamada runs through charts of the S&P 500 in order to decipher what could be ahead for stocks. The analyst also shares her investment outlook and investment approach. PRO members can access the full interview here.