It’s clear that a strong El Nino pattern has developed over the United States as Iowa farmers prepare for the upcoming harvest season. But weather experts are mixed on how El Nino will impact Iowa’s 2015 harvest.

Some predict a favorable dry weather pattern that will allow corn to dry naturally in the field and open a wide window for farmers to bring home the crops. While others expect El Nino to trigger added rainfall in some parts of the state, which could turn fields soggy and harvest into a slog.

Conversely, weather experts do agree on El Nino’s effect on Iowa’s winter weather. The weather pattern, they say, is likely to...