The Eclipse May Require a Coat
Maybe you can bring a parka.
In some places the difference could be double digits
According to the Washington Post, areas where the eclipse reaches totality will see a sudden drop in temperature. The Post tells us nighttime cool downs are gradual. The eclipse brings sudden darkness. In some places, the difference could be double digits in a matter of a couple of minutes.
While this would be a concern in winter, most people watching in Idaho will likely appreciate the brief chill especially following a hot summer.