UK referendum could be close and that could help BTC. Might be a bigger factor than the halving which I think is overplayed. What will be fascinating (and possibly frothy) is if we see two or more factors go the same direction at the same time (Ex. if we had both halving, the developers/miners/etc agreed on a road map to increase the block size, and MtGox bankruptcy starts payouts).
Global economy continues to look bad. It's not a worldwide recession by any means, but if a couple things go wrong (ex. Trump starts a trade war with China, energy/mining bankruptcies lead to problems with large banks/investment firms, one or more bubbles collapse, or Russia does something crazy).
I was just at the local Trader Joes and they had the largest lineup I've seen (line up to get in the store, and then inside the store the line literally snakes through the entire store and has to double back) - as people around here tend to panic a bit about storms (rain or snow). Even though we had three feet several years ago, so people are aware of what snow is =)