That said, the locations of the Hadley cells changes depending on how much heat is stored in the system, and adjustments to this is part of the whole El Niño, La Niña cycle. As you increase the rate of energy storage, this results in various chaotic changes, that can increase extreme events.

But the real problem with the rarity of the event is that you arrive at that figure by a probability model assuming independent storms, probably with a Poisson model for frequency. However storms are not actually independent events. If you have a stable pattern that results in many storms following the same track to Boston, the odds of an extreme event are way higher than the naive probability model would have suggested.