CNBC’s Jim Cramer on Monday said there could be an opportunity to buy stocks ahead of a possible rally.”The charts, as interpreted by Larry Williams, suggest that Christmas is not going to be canceled for Wall Street — he thinks we still have a Santa Claus rally coming, and the ideal time to buy is sometime around this Thursday,” he said. Stocks fell for a fourth consecutive trading session on Monday, weighed down by mounting recession fears. Cramer said that the market’s recent downturn is the perfect setup for a Santa Claus rally, which describes US stocks’ tendency to rise near the end of the year and the beginning of the new year. For Williams, it’s a matter of when, not if, stocks will run up, according to Cramer. To explain Williams’ analysis, he examined the daily chart of the S&P 500 futures from November 2021 to January 2022. Zoom In IconArrows pointing outwardsThe blue line at the bottom is Williams’ seasonal forecast, and suggests the best buying opportunities come in mid-to-late December, with the Santa Claus rally tending to last through January 10. The chart shows that stocks rallied from December 20 through the end of the year, in line with the forecast. Cramer then compared these findings to the data shown in the daily chart of the S&P futures from September of this year until now. Zoom In IconArrows pointing outwardsThe chart suggests that the market just entered the “seasonal sweet” spot,” Cramer said. He added that Thursday’s trading session would be the ideal moment to buy ahead of a potential rally, according to Williams.”I know it’s hard to believe that the market’s ready to run, but that’s how it always is with Larry’s calls. Although it’s possible this year will be different, historically, betting against him has been a real bad strategy,” he said.For more analysis, watch Cramer’s full explanation below.Jim Cramer’s Guide to InvestingClick here to download Jim Cramer’s Guide to Investing at no cost to help you build long term wealth and invest smarter.