We'd have to look at every predictor to know, but let's have a look at Iowa's track-record:
Sometimes one party has no contest. I'm not giving Iowa credit for picking the ONLY guy in the race, nor for calling a TIE for nomination since that's impossible. Otherwise, one point for picking a party nominee.
2008: Iowa gave us Obama vs Huckabee for 1/2 of possible points.
2004: Iowa gave us Kerry. 1 more, 2/3 total.
2000: Iowa gave us Gore vs Bush. Perfect. 3/5 total.
1996: Iowa gave us Dole. 4/6 total.
1992: Iowa gave us Harkin. 4/7 total.
1988: Iowa gave us Gephardt vs Dole. 4/9 total.
1984: Iowa gave us Mondale. 5/10 total.
1980: Iowa gave us Carter vs Bush. 6/12 total.
1976: Iowa gave us Uncommitted vs Tie. 6/14 total
1972: Iowa gave us Uncommitted. 6/15 total
Before that, it's harder to find data so screw 'em. Call it. Final score: 40%.
There you have it. Winning Iowa generally means you DON'T get your party's nomination.