After months of trading in a well-defined range, the is about to see a major move, says one top technician.

"This is the single most important chart on my screen," Rich Ross told CNBC's "Trading Nation" on Wednesday. The index bounced from a 16-month low in the session, but according to Ross it's now sitting at a dangerously fragile level.

"We established a very important bullish reversal at this key support [around 93]," Evercore ISI's head of technical analysis said. The index briefly dipped below this level earlier in the week but quickly recovered.

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But for Ross, rather than confirm a reversal in trend, the hold is merely a delay of further losses. "I actually think that after a short-term bounce we could actually break below [93]," he added.

Ross noted that beneath the 93 support area, the possibilities for losses could be endless. "A break below that level could take you all the way down to the 86 level on the dollar," he said. That's a more than 7 percent move lower than current levels and puts the index at levels not seen since October 2014.

The move lower would mark an end to the torrid run in the dollar, which rallied more than 27 percent from the low of 78 in May 2014 to the high of around 100 in December 2015. The decline in the dollar has been supportive of commodities and oil in particular, which has helped the S&P 500 surge 13 percent from its February lows.

"[A breakdown] would be bearish for the dollar and bullish for crude oil, emerging markets and other commodities," Ross said. "It would also, unfortunately, be bullish for the yen and euro, which is a negative for Japan and Europe."