During July and August, warm nights may accelerate maturity of corn to the detriment of yield. In most areas of Iowa, 2015 and 2016 were much alike for corn. In this case, nighttime temperatures may indeed be the major factor resulting in a yield improvement or diminished yield in 2016 since warm nights accelerate maturity and thereby reduce yields.
Look at July and August—the period from silking to maturity. If nights are mainly warmer than usual (red) the yield is reduced. Nights cooler than usual (blue) tend to enhance yields.
Automated Data Plotter
Click here to access the Automated Data Plotter on the Iowa Environmental Mesonet and pick a city near a farm of interest to make the graphic (or select the reporting district of interest or statewide, if desired). For your interest, pick a high yield year (2009 perhaps), and then a low yield year (2012 or 1995 for example) and note the July-August temperature deviation (blue vs red).
Remember.... this is a good indicator by itself ONLY when the years are otherwise similar.