What weather phenomenon was the Norse god Thor thought to control?

Thor is a prominent god in Germanic paganism. In Norse mythology, he is a hammer-wielding god associated with lightning, thunder, storms, sacred groves and trees, strength, the protection of mankind, hallowing, and fertility. Besides Old Norse Þórr, the deity occurs in Old English as Þunor, in Old Frisian as Thuner, in Old Saxon as Thunar, and in Old High German as Donar, all ultimately stemming from the Proto-Germanic theonym *Þun(a)raz, meaning 'Thunder'.

Thor is a prominently mentioned god throughout the recorded history of the Germanic peoples, from the Roman occupation of regions of Germania, to the Germanic expansions of the Migration Period, to his high popularity during the Viking Age, when, in the face of the process of the Christianization of Scandinavia, emblems of his hammer, Mjölnir, were worn and Norse pagan personal names containing the name of the god bear witness to his popularity.