Although no humans were there to witness the giant comet of 65 million years ago, in this case it really did portend disaster.
-- Walter Alvarez, T. Rex and the Crater of Doom
With mortal crisis doth portend My days to appropinque an end.
-- Samuel Butler, Hudibras. Part i. Canto iii. Line 589 ,
I see five separate moving clouds of dust; they portend some sort of magic.
-- Laurie Fox, My Sister from the Black Lagoon: A Novel of My Life
Many signs portended a dark and stormy day.
Portend comes from Latin portendere, to indicate, to predict, from por- (variant of pro-), before + tendere, to stretch out, to spread. Thus that which portends is that which stretches out before us into the future.