It seems like a top-ranked NCAA team loses every time a day ends in "Y" this season. With the top of brackets as unstable as astatine-213, it's time to ask: Could this finally be the year a No. 16 seed takes down a No. 1?

The Giant Killers statistical model tells us it's not actually likely that a No. 1 seed will become the first ever to lose its first March Madness game, but the odds are much better than we have seen in recent seasons. We estimate there's a 27 percent to 30 percent chance of an upset in 2013, compared with a range of 7 percent to 17 percent in tournaments since 2007. And if the right Killer steals an auto bid and gets seeded against a vulnerable Giant, the probability of an enormous upset could zoom to more than 40 percent. This season, it will make sense to pause at least a moment before advancing No. 1 seeds through your brackets.

Allow us to explain why and show you which potential No. 16 seeds have the best chance of pulling an upset, and which potential No. 1 seeds are most vulnerable.