From "Scientific" American: Montana is allegedly much warmer than it was in the 1950s, and wheat yields have "increased exponentially" since then

[Given a huge increase in wheat yields along with warming temperatures, here's the conclusion]

A new analysis reveals that higher average temperatures in Montana over the last six decades equal less wheat.
...
Plant scientist Luther Talbert of Montana State University and his colleagues looked at weather records for the Mountain State from 1950 to 2007. The month of March has had the most warming overall, increasing by nearly 0.1 degrees Celsius per year on average. As a result, farmers now plant wheat 10 days earlier.

In addition, higher temperatures in July linked up to less wheat to harvest and lighter grains.

In 2007, the U.S. grew 12.8 million metric tons of hard red spring wheat, which is primarily used to make bread. Yields of this staple grain have increased exponentially since the 1950s because better farming practices and new wheat breeds have more than made up for those hot Julys.