Because clear nights allow for rapid cooling, temperatures in Petrified Forest National Park can vary as much as 40 F between the highs of daytime and the lows of night. Summertime temperatures, from late May to early September, are in the mid to high 90s F, yet go down to the mid 60s F overnight. Winter temperatures, November to March, often average in the teens and 20s F at night with daytime sunshine warming the area up to the 40s or 50s F.