"...One variety of weather phenomena that exemplifies the 'Dangerous' category is extra-Equestria systems, more commonly known as 'wild storms'. These originate outside the borders of Equestria and move inwards, wreaking havoc over any lands they cross. These systems are not built or managed by pegasi, instead being manifested by unknown forces and acting without direction or goal. As such, they are highly unpredictable and often are characterized by vicious cross-winds, lightning storms, hail, and immense size. Such storms are immediate A-2 category significance, and all available weather workers are to muster and develop a plan to disperse or divert these dangerous systems with all haste. However, no fewer than six pegasi should take action against a wild storm, and it is highly preferable that a full wing of a dozen work together. Should a lone flyer come into contact with a wild storm, immediately flee the area and report to the nearest town or city containing a branch of the Weather Workers..."
-excerpt from the Manual of Meteorological Manipulation