An Overview of the Formation of Nighttime Thunderstorms

What is it about?

Nighttime thunderstorm formation is more difficult to anticipate and forecast than daytime thunderstorm formation. A major component of the Plains Elevated Convection at Night (PECAN) field campaign in the U.S. Great Plains was to study the formation of nighttime thunderstorms. In this article, we summarize different formation types observed during PECAN: 1 June–16 July 2015. These NCI types, classified using PECAN radar composites, are associated with 1) a cold front, 2) the low-level jet (LLJ), 3) a preexisting large thunderstorm system, 4) a bore or density current, and 5) no obvious forcing mechanism (pristine). An example and description of each of these different types of PECAN events are presented. The University of Oklahoma real-time 4-km Weather Research and Forecasting (WRF) Model ensemble forecast runs illustrate that the above types having larger-scale organization (e.g., associated with cold fronts and near a preexisting thunderstorms) were better forecasted than the pristine type. Based on current knowledge and data from PECAN, conceptual models summarizing key atmospheric features are presented and physical processes underlying the development of each of these different types of thunderstorm formation events are discussed.

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Why is it important?

Nighttime thunderstorms contribute to the nighttime rainfall maximum in the central U.S. Forecasting skill for nighttime thunderstorm formation is worse than that for daytime thunderstorm formation. A better understanding of the different types of nighttime thunderstorm formation mechanisms may improve forecasting skill of nighttime rainfall.

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