Astraphobia
An abnormal and persistent fear of thunderstorms.
Sufferers experience anxiety even when they realize the risk of harm is very small.
Consequently, when indoors they might seek shelter under a bed, in a closet or in a basement.
They generally keep a watchful eye on the sky and remain alert for reports of electrical storms.
'Astraphobia' is derived from the Greek 'aster' (star) and 'phobos' (fear).
Related term: Brontophobia: Fear of thunder.