Nocturnal Severe Thunderstorms Over the Great Plains: Environmental Differences Among CI Modes and Storm Types

Severe-weather potential in thunderstorms typically decreases throughout the night as a near-surface stable layer is created and forcing for convection initiation decreases. Many thunderstorms, however, produce severe weather at night, including damaging winds and tornadoes, despite this near surface stable layer. During the warm season over the Great Plains there is a nocturnal maximum in thunderstorms, many of which are severe. In a 20-year climatology, we identified three different modes of nocturnal CI: events that initiate on a surface boundary, events that initiate on the cold side of a surface boundary, and events that initiate with no nearby surface boundary. The characteristics of severe storms differ among the modes. For example, approximately half of the events that initiate on a surface boundary and half of the events that initiate on the cold side of a surface boundary are severe while only one quarter of the events that initiate without a nearby surface boundary are severe. A 20-year climatology of severe nocturnal thunderstorms will be presented and each type of severe event (including hail, wind, tornadoes, and flooding events) will be examined to identify environmental characteristics not present in the non-severe events.