Adam Clarke on Habakkuk 3:4

He had horns coming out of his hand - קרנים karnayim, rays. His hand - his power - was manifested in a particular place, by the sudden issuing out of pencils of rays, which diverged in coruscations of light, so as to illuminate the whole hemisphere. Yet "there was the hiding of his power." His Majesty could not be seen, nor any kind of image, because of the insufferable splendor. This may either refer to the lightnings on Mount Sinai or to the brightness which occasionally proceeded from the shechinah or glory of God between the cherubim, over the mercy-seat. See Capellus and Newcome. If lightnings are intended, the dense cloud from which they proceeded may be meant by the "hiding of his power;" for when the lightnings burst forth, his power and energy became manifest.

Probably from this the Jupiter Keraunos or Jupiter Brontes of the heathens was borrowed; who is always represented with forked or zigzag lightnings in his hand.