Bismarck has a classic continental climate — short, hot summers and very long, very cold winters. July is the warmest month, with average highs around 29°C (85°F), and conditions are genuinely pleasant for outdoor activities along the Missouri River. The Fort Lincoln and Double Ditch sites are best in summer when the sites are fully open and the weather is dry.
Winter is brutal: temperatures regularly drop below -20°C (-4°F) and blizzards are common from November through March. Driving conditions can be treacherous and some outdoor sites close or are difficult to access. Spring and autumn are brief transition seasons — April and May can be muddy and cold, while September and October offer the best combination of milder weather and reduced tourism. The Bismarck-Mandan area hosts the United Tribes Technical College International Powwow in early September, one of the larger powwows on the northern Plains and worth planning around.