A climatology of the origin, movement, duration, and termination of convective systems in the north-central United States

Lighting observations from the summer season of 2004 were used to develop a climatology of the origin, movement, duration, and termination of convective systems in the north-central United States. Previously-proposed mechanisms of nocturnal convection were assessed based on the characteristics of the convective systems. Most nocturnal systems that occurred in the central plains and Great Lakes region formed upstream and propagated into these regions. Nearly 60% of non-local nocturnal systems in the central and eastern plains (99.9°W-90°W) formed near the Rocky Mountains, typically during the afternoon hours. These results support earlier work suggesting that the nocturnal precipitation maximum in the central United States is largely due to propagating systems from the lee of the Rocky Mountains. Additionally, the findings suggest that propagating systems that form farther eastward in the central plains contribute to nocturnal convection in the Great Lakes region. Locally-formed nocturnal convection was also observed. The majority of local nocturnal systems formed during the nighttime or morning hours when the low-level jet is climatologically most frequent. Convection that formed over the Great Lakes at all times of the day was often short-lived, and propagating systems typically terminated within 2 hours after moving over the Great Lakes. These observations suggest that the lake surfaces, which are typically cooler than the surrounding land surfaces especially during the daytime hours, inhibit convection.