Perpetual Storm creates the Storm battlefield effect in all battles while the global is active. It also prevents all flying units that do not have the flies in storms ability (eg - Air Elementals and Queens of Elemental Air) from flying over land. This reduces the map movement of most flying units by one, removes the ability to ignore terrain penalties, and prevents them from moving over enemy territory or attacking enemy territory from non adjacent provinces. As the spell description states, it also closes all mountain passes, preventing any unit that does not both have flight and the ability to fly in storms from passing through them.
Because Perpetual Storm is activated in the magic phase, any movement orders that become impossible due to the effects of the Perpetual Storm are cancelled.
Perpetual Storm raises unrest in all provinces worldwide.