From Wikipedia:
Weatherman, known colloquially as the Weathermen and later the Weather Underground Organization, was an American radical left organization founded in 1969 by leaders and members who split from the Students for a Democratic Society (SDS). The group organized a riot in Chicago in 1969 and bombed buildings in the 1970s.
They took their name from the lyric "You don't need a weatherman to know which way the wind blows," from the Bob Dylan song Subterranean Homesick Blues. They also used this lyric as the title of a position paper they distributed at an SDS convention in Chicago on June 18, 1969, as part of a special edition of New Left Notes. The Weathermen were initially part of the Revolutionary Youth Movement (RYM) within the SDS, splitting from the RYM's Maoists by claiming there was no time to build a vanguard party and that revolutionary war against the United States government and the capitalist system should begin immediately. Their founding document called for the establishment of a "white fighting force" to be allied with the "Black Liberation Movement" and other "anti-colonial" movements to achieve "the destruction of US imperialism and achieve a classless world: world communism."