..wasn't this expected?...is this lighting bolt out the blue?
Not necessarily. The 'Rats managed to recruit their best-known candidate, and one who is somewhat less liberal than other Colorado 'Rats. Meanwhile, the Republican primary got nasty, and Coors is an untested, first-time candidate. So it wasn't inevitible that things would come together like they have.
Actually this is great news considering the Rat had a double-digit lead a month ago.