ʿĀdah denotes the ordinary observed order in which certain circumstances are customarily followed by certain outcomes. Khāriq al-ʿādah refers to an event departing from that order.
An extraordinary occurrence is not, simply by being extraordinary, a logical impossibility. An unexpected transformation may contradict normal experience, but its mere rarity does not validate an unrelated claim to prophethood.
The evidential force of a sign depends also on its setting, its relation to the claim and the failure of credible opposition to match it.