Kinematics, Thermodynamics, and Microphysics of the 25-26 June 2015 Kansas MCS during PECAN

Abstract

This case study analyzes a nocturnal mesoscale convective system (MCS) that was observed in northeast Kansas as part of the Plains Elevated Convection at Night (PECAN) field experiment on 25-26 June 2015. Over the course of the observational period, a broken line of nocturnal convective cells initiated around 0230 UTC on the cool side of a stationary front and subsequently merged into a quasi-linear MCS that later matured and developed strong outflow and a trailing stratiform region. This study combines radar observations with mobile and fixed mesonet and sounding data taken during PECAN to analyze the dynamics, thermodynamics, and microphysics of the MCS from 0300 to 0630 UTC. This study is unique in that 38 consecutive multi-Doppler wind analyses were studied over the 3 and a half hour observation period allowing for a long-lived analysis of the evolution of the kinematics and microphysics of the nocturnal MCS. Radar analyses indicated that the initial convective cells and linear MCS were elevated which is supported by the Hiawatha mesonet site which showed gradual cooling due to precipitation evaporation. During upscale growth, individual convective cells developed storm scale surface-based cold pools which were measured by MM1. By 0500 UTC, the linear MCS was surface-based and a bowing MCS developed which produced a wind report 20 minutes later. The mobile and Kansas mesonet sites recorded a large temperature drop when the convective lines passed over and a similar final theta-v value indicating the homogeneity of the cold pool over time. Trajectory analysis using diabatic Lagrangian analysis confirms the conclusions from the observations showing that parcels from below 500 m were being ingested in the convective line updrafts of the MCS indicating that the system was at least partially surface-based. The transition from elevated to surface based was due to the formation of a surface-based cold pool that was driven by diabatic cooling due to graupel melting and rain evaporation. In this environment, the elevated system became surface-based when the cold pool lifting was sufficient for surface-based parcels to overcome the CIN associated with the frontal inversion.