Notes
Since the Thunderstorm Effect sprites cover an area of 2×2 map fields and it was initially intended to be used on multiple juxtaposed fields (triggered by area spells), the overlapping of sprites was avoided by having every other map field to display a blank (transparent) sprite.
This, however, had a negative side effect when it was intended to be triggered on single map fields. For example, when a character would use an equipped The Rain Coat, there would have a map field on which no effect would be noticed for every juxtaposed field that would correctly display the effect's specific sprites.
In order to fix this, this effect which does not skip juxtaposed map fields was implemented.