[dyestymum]

As I said earlier I'm sure there's some logical explanation for why some contrails disappear within a few minutes and others are there for a while.

Well yes, there are different layers of atmosphere, almost like an onion, with differing layers of humidity, temperature, and percipitation. This will more than likely result in a contrail lasting a bit longer, but the entire day? Also, since the humidity that day was low enough to prevent cloud formation, I'm assuming that contrail formation would remain at a minimum.