Multiscale Processes Leading to the Development and Longevity of a Mesoscale Convective System

Nocturnal mesoscale convective systems (MCSs) frequently develop over the Great Plains in the presence of a nocturnal low-level jet (LLJ), which contributes to convective maintenance by providing a source of instability, convergence, and low-level vertical wind shear. While these nocturnal MCSs often dissipate during the morning, many continue into the following afternoon despite the cessation of the LLJ with the onset of solar heating. A lack of understanding currently exists about which environmental factors control the daytime persistence of nocturnal MCSs.

Routine observations, RAP analyses, and a convective-allowing WRF-ARW simulation were utilized to understand the evolution of a long-lived MCS on 6 October 2014. Elevated convection developed in response to a frontal merger in central Oklahoma, which subsequently grew upscale into a quasi-linear convective system (QLCS). The western portion of the QLCS reorganized into a bow echo with a pronounced cold pool and rear-inflow jet (RIJ) as it encountered increasingly unstable air supported by the LLJ. Differential advection relating to the interaction of the nocturnal LLJ with the topography of West Texas was responsible for establishing considerable heterogeneity in moisture, CAPE, and CIN within the environment, which influenced the structure and evolution of the MCS. An inland-advected moisture plume over central Texas led to rapidly-increasing CAPE during the nighttime, which reduced the reliance of the MCS on the LLJ as the source of instability prior to sunrise. Therefore, convective dynamics in tandem with mesoscale variability influenced by the geography of the southern Plains enabled the daytime persistence of the MCS.