Art Cashin of UBS Financial Services said markets got a bounce partly due to oversold conditions.
Major indexes are higher across the board with the and Nasdaq looking to snap three-day losing streaks after global growth concerns and geopolitical tensions have soured markets the past several sessions.
Read MoreWatch Art Cashin: Global growth concerns weigh on markets
"You had a bit of an opening bounce," Cashin said. "That rolled over and then the bulls found salvation on the cocktail napkins because we stopped at the 50-day moving average on the S&P: 1,978."
Cashin cautioned there are concerns about how markets will hold up the rest of the week. This week has a downside reputation: There's an old tradition to sell on Rosh Hashanah and wait until Yom Kippur to buy.
Wednesday's rally may be due to the buy-the-dip crowd, which waits for major averages to fall several percentage points before getting back into the market. (Think: Buy low, sell high.) The Dow Jones Industrial Average, for instance, is on track for its best day five weeks.
"Thursday and Friday will be very interesting," Cashin noted. "If [stocks] roll over and go south again, then people may take a slightly more cautious look. But if they continue on the upside, everybody is going to say: It happened again. A 2 or 3 percent drop, and you had to buy the dip."