"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.
Thanks, but you didn’t have to Google it. I included it in the original posting. Scroll up to the top.