Weather can make or break a roadtrip, so here's some data about year-round temperatures in Atomic City to help you plan yours: The hottest months are usually July and August with an average temp of 66°F, while the coldest months are January and December with an average of 21°F. The snowiest months in Atomic City are January, March, April, and November, with each month seeing an average of 13 inches of snowfall.