It's not just Republicans who will make the difference on Tuesday; Iowa voters may register as a Republican on caucus day, meaning that independents could also influence the outcome.
Those independents will most likely support Paul, says Kedron Bardwell, chair of the political science department at Simpson College—it's just a question of how many come out.
"The one thing you don't know about Ron Paul supporters is exactly how many independents will show up at the site and register as republicans," says Bardwell. "They don't have any Democratic caucus to compete for their votes."
Those independents would add to Paul's rock-solid base of support, which helped him to a second-place finish in the August straw poll. Steve Payne, a homemaker from Des Moines, is an independent-turned-Republican who plans to cast his vote for Paul—even through the general election.
"If I have to, I'm probably going to write in Ron Paul [in November]," he said at a Ron Paul event Monday in Des Moines.
In addition to candidates' event appearances, campaign ads will certainly affect voters' choices.
Newt Gingrich has consistently spoken out against negative ad campaigns over the past week. A barrage of negative ads from opponents is credited with contributing to Gingrich's waning poll numbers.
Yet many voters say the recent glut of negative ads has had a counterproductive effect on them.
"The candidates don't need to be continually running each other down," said Wayne Burkhart of Woodward, who works for Costco, at a Sunday Gingrich event in Ames. The chair of his precinct, Burkhart is still undecided about whom to vote for, but says he is turned off by negative ads.
Still, says Bardwell, those ads are effective on the whole.
"There's a pretty strong consensus in political science that negative ads do work," he said.
Whatever eventually makes the difference, it won't be the weather. Today's forecast for much of Iowa features plenty of sun and above-average temperatures.