While lightened volumes due to Christmas could make for extra volatility, the market's seasonal bias strongly suggests that investors should bet on stocks this week.
"It's going to be a merry Christmas for everyone—if they're long equities," predicted Anthony Grisanti of GRZ Energy. "I definitely think this week, the market goes higher. Five out of the last six years, the market rallies into the last two weeks of the year."
The historical statistics are compelling. Looking at the performance of the S&P 500 from December's post-Christmas trading sessions through the second session of January, the market has posted a 1 percent gain on average, rising 71 percent of the time.
The trend also looks good in a slightly longer-term context. If one bought the S&P on Dec. 20 and sold it on Jan. 7 (or the subsequent day on which the market was open) one would have enjoyed 17 winning trades over the past 20 years, for a total return of 337 S&P points on the trade.
(Read more: Which stocks should be in Santa's sack?)
The phenomenon is known as the "Santa Claus Rally," though that term technically refers only to the generally positive performance of stocks in the last five trading days of the year and the first two of the new year. The trend was discovered in 1972 by Yale Hirsch, the creator of the Stock Trader's Almanac.