One of the thing that makes it difficult to forecast primaries (as opposed to general elections) is that people tend to make last second decisions.  This problem is not because primary voters are more indecisive than general election voters, but mostly because they have more choices.  In the general, 96% of the voters know well in advance whether they will be voting Republican or Democrat.  In a primary, voters have to choose which Republican or which Democrat will best represent them and their party in the general election.  That choice involves every voter deciding what is more important — pragmatism or ideology.