I saw a graphic earlier that they are calling for an %80 chance of snow in Iowa. I actually happen to think this election is the one that is more fluid than any other. So many strange things are happening (the Cruz mailer, the rubio surge, trump not showing to the debate, the mismedication of Dr. Ben Carson so that he looks like he is gonna fall asleep on stage)... The polling could be correct for 3 days ago, and still not portray what we will see Monday.
The vast majority of the snow is supposed to come down after 12 AM on Monday night, after the caucuses are over. The southwestern part of the state may get a little bit of rain mixed with snow during the caucuses, but that's it. At least that's what they're predicting right now.