La Nina conditions currently exist in the tropical Pacific and will influence winter conditions across the Northern Hemisphere. Certain weather conditions become more likely in certain areas during La Nina and this winter's outlook is mostly based on these historical La Nina conditions. For current information on the ongoing La Nina, click here.
The official forecast for Iowa can be seen in the two following images which indicate equal chances for above, normal, and below normal temperatures and precipitation for central Iowa. A more detailed analysis of winter conditions during La Nina in Iowa can be found here.