Across eastern North Dakota and northern Minnesota, more than half of our thunderstorms in summer happen overnight. This is due to a low-level jet stream, known as the Nocturnal Jet, which often forms at night about 1-2,000 feet above the ground. These nighttime storms can be weak or strong, depending on conditions, but rarely make tornadoes. Most Northern Plains tornadoes happen in the afternoon or evening. The air at night often cools near the ground more than at upper levels, causing a stabilizing effect. Severe storms can still rage when their energy comes from higher up, but it is hard for these storms to generate tornadoes. However, when surface conditions are able to remain unstable after dark, a middle of the night tornado becomes a rare but frightening possibility.
