Over at Politico, Larry Sabato predicts that the GOP will pick up four to eight seats in November. The Senate flips at six seats; at five, the Dems have Biden to break a tie. Sabato ranks the likelihood of seats flipping by state, from most to least likely: South Dakota, West Virginia, Montana, Arkansas, Louisiana, Alaska, North Carolina, Iowa, Colorado, Michigan, New Hampshire, Minnesota, Virginia, and Oregon.
As you watch polls between now and November, if the GOP does well in the states towards the bottom of that list, you may see a Republican wave breaking. Conversely, if the Dems look good in the states near the top of the list, 2014 may not be so bad for them.