Fog becomes more likely later in August

Plot showing the number of fog observations at the Eastern Iowa Airport by date and time of day. The circled area highlights August mornings. (IOWA ENVIRONMENTAL MESONET)
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CEDAR RAPIDS, Iowa (KCRG) - While summer fog isn’t common in Iowa, the back half of August does see a spike in the morning hours, especially between 4 a.m. and 8 a.m. We’re starting to see that change, since the past three mornings have featured fog over portions of eastern Iowa during those hours.

This is due to maturing crops transpiring moisture into the air, along with a rapid loss of daylight. These longer nights and high humidity values lead to an increased potential of fog. Since the crop is late this year by a week or two, the risk of foggy mornings may extend well into September.