Yes. There are. To best understand how the turnip stalk market works, I suggest reading this. Dataminers put this together to explain exactly how turnips work in NH.
If this is the first time anyone has ever bought Turnips on your island, you're automatically guaranteed to have a "Small Spike" pattern, which will always result in a modest profit. If you're not TTing and today is currently Thursday/Friday in-game, I believe that the Small Spike can see its maximum amount of decreases on Thursday's AM price, and it only goes up from there. So unless you bought Turnips before this week, or you missed checking a price, you should be seeing decent increases soon.