The Dow is coming off its best August since "Ghostbusters" dominated the Billboard's top 100 list 36 years ago.
But it's the next four weeks that could give investors a scare.
Ally Invest's Lindsey Bell predicts volatility will make a big comeback due to seasonal trends combined with rising uncertainty.
"In September, you usually see the chance of a positive return on the month very low — below 50%," the firm's chief investment strategist told CNBC's "Trading Nation" on Monday. "We are going to see the rubber really hit the road."
She ranks uncertainty as September's biggest overall market risk. Bell cites the stalemate over a second virus relief package on Capitol Hill, upcoming fiscal budget debates, the presidential election countdown and corporate conference season as headwinds.
"With the increase of uncertainty, you're going to see an increase in volatility," said Bell. "We've seen it today. The VIX index is creeping back up."
The VIX, or CBOE Volatility Index, is considered the market's fear gauge and reflects future volatility over a monthly time span. Over the past two months, the index is down more than 13%. But it's up 18% over the last five sessions.
Bell expects the uncertainty to drive frequent 1% to 1.5% daily swings in September.
"As we get closer to the election and some of these other events, it gives room for that type of volatility in the market to return," she said.
Bell, who has been taking a barbell approach to investing, suggests using weakness as a strategic opportunity. She believes cyclical or value groups will eventually find solid footing on better news surrounding the coronavirus and a vaccine. She uses the consumer discretionary group as an example.
"You may want to consider rotating out of the bigger names like an Amazon or Home Depot ... which have done very well and have helped carry the sector into some smaller names that haven't done as well on a year-to-date basis," said Bell, a CNBC contributor.
But she wouldn't buy value at the expense of the year's winners.
"Remain in some of these growth and tech areas that have continued to do well," Bell said. "You can hide out there to an extent because they don't necessarily need economic growth to do well."