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Growing Climate
Iowa generally has hot summers, cold winters, wet springs, and sometimes unpredictable falls. Summers are warm and humid with daytime temperatures averaging 74°F (23°C) in July. Tropical air masses from the Gulf of Mexico bring frequent thunderstorms, with persistent rain in June. Winters are cold, with January temperatures averaging about 14°F in the northwest and 22°F in the southeast. 
Snowfall, however, is moderate compared to some other states. Iowa’s climate typically supplies sufficient precipitation to foster successful grape production, but seasonal droughts do occur, and soil characteristics can negatively impact moisture availability.
Iowa's climate presents grape growers with a challenge. As has been proven on at least two occasions over the past century or so, Iowa winters can be bitterly cold and absolutely lethal to many grape varietals. Late spring frosts can damage vine buds, and hot humid summers can contribute to the development of molds and mildews, which can be difficult and expensive to control. Finally, Iowa’s growing season is relatively short.
More than any other factor, Iowa’s climate is the major influence on the grape grower’s choice of which grape varietal to plant. Grapes have to be tolerant of Iowa’s wide swings in temperature and humidity, they must produce fruit within a relatively short growing season, and the ability to bear fruit from a secondary bud break (even after the first one has been damaged by an early spring frost) is a desirable characteristic.
