A bust for the S&P 500 just in time for spring? That’s what one market technician says could be in the pipeline if a bearish chart pattern he’s watching pans out.

Sven Henrich, otherwise known as NorthmanTrader, flags what’s known as a rising-wedge pattern that he says points to a potential 20%-to-25% meltdown by spring. It’s a negative technical signal that starts wide at the bottom of the chart and narrows as it moves up, in step with rising prices and tighter ranges. It’s polar opposite to a bullish falling-wedge pattern.

Read:Why stocks are primed for a meltdown in the spring

Northman says the index has experienced this rising-wedge bust several times, including in the 1980s and 1990s, and then in 2000 and 2008.

Here’s a monthly chart for the S&P SPX, +1.05% in his blog post that shows how that pattern has developed over the years. He’s had his eye on the latest rising-wedge pattern since 2015.

NorthmanTrader.com

Henrich says this rising wedge is developing alongside “extremely steep support lines,” with the market still completely uncorrected. He notes that while there’s no guarantee that a wedge go to a peak apex, this wedge is getting harder and harder to sustain. Piling on the pressure are concerns about a brewing U.S. recession and presidential election uncertainty, he noted.

“Every major top in the past 30 years has come on rising wedges with major negative RSI (relative strength index) divergences,” he tells MarketWatch. “And every one retraced between 0.50% and 0.618% of the move at least. Every time.”

As for how investors should prepare for a potential big drop for the S&P 500 by spring, Henrich says his strategy has been to sell into strength over the past two months. “As a long-term investor, my personal view would be to not be afraid, to have some cash and be able to adjust. Valuations are high and using strength to diversify into some cash is probably a solid idea,” he said.

After all, as he points out, billionaires are holding nearly 22% cash.

Now on its face, a 20% drop for the S&P 500 would potentially put it into a bear market. The “Northman” blogger says that up to a 20% drawdown is correction territory, and a sustained move over that yardstick would be considered bear-market territory.

“So yes, if we dropped below 1,745, if current highs stick, then that would be a bear move,” he said.

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His view is not exclusive to the S&P 500. On his website, Henrich lays out a couple of other charts that show corrections looming, such as in Facebook shares FB, +2.66% .

NorthmanTrader.com

There’s also this “extremely steeply rising wedge” for the exchange-traded fund that charts high-yield bonds, the SPDR Barclays High Yield Bond JNK, +0.31% . Henrich said a break lower could “seriously test this year’s rally.”