My highly uneducated guess on this would be that the water molecules moving up are cooling down a tiny little bit. Being cooler would then be making it unable

My highly uneducated guess on this would be that the water molecules moving up are cooling down a tiny little bit. Being cooler would then be making it unable for them to climb further when a certain threshold is reached, meaning they would need the surrounding environment to heat it up a little again to allow it to move further.