I wrote a post before the primary election on predicting turnout. That was quite a bit more involved since there was the issue of the new summer date to consider. Predicting turnout this Tuesday should be a little more straight forward since there are not really any unknown variables to consider, unless you think there will be a GOP surge.
I'm not discounting that possibility, I just don't think that it will have nearly the same effect in Minnesota where we already turnout at a high rate.