July has already been more humid than average, and now another, less obvious factor will enhance humidity this week: corn sweat. Like a person breathing, corn exhales water vapor through its leaves — a process called evapotranspiration — which exacerbates humidity in agricultural regions during the summer.

As Illinois braces for another summer heat wave, this week's conditions will be worsened by an unusual weather phenomenon: corn sweat.

The heat wave baking the central United States this week may feel worse than those earlier in the summer, and corn is partly to blame, forecasters say.