Nocturnal Elevated Convection Initiation of the PECAN 4 July Hailstorm

Abstract

During the Plains Elevated Convection at Night (PECAN) experiment, an isolated hailstorm developed on the western side of the PECAN study area on the night of 3–4 July 2015. One of the objectives of PECAN was to advance knowledge of the processes and conditions leading to pristine nocturnal convection initiation (CI). This nocturnal hailstorm developed more than 160 km from any other convective storms and in the absence of any surface fronts or bores. The storm initiated within 110 km of the S-Pol radar; directly over a vertically pointing Doppler lidar; within 25 km of the University of Wyoming King Air flight track; within a network of nine sounding sites taking 2-hourly soundings; and near a mobile mesonet track. Importantly, even beyond 100 km in range, S-Pol observed the preconvection initiation cloud that was collocated with the satellite infrared cloud image and provided information on the evolution of cloud growth. The multiple observations of cloud base, thermodynamic stability, and direct updraft observations were used to determine that the updraft roots were elevated. Diagnostic analysis presented in the paper suggests that CI was aided by lower-tropospheric gravity waves occurring in an environment of weak but persistent mesoscale lifting.

The Mechanism and Predictability of an Elevated Convection Initiation Event in a Weak-Lifting Environment in Central-Eastern China

“…Nocturnal mesoscale convective systems (MCSs) frequently occur in many places in the world such as the central United States (e.g., Maddox 1980;Carbone et al 2002;Parker 2008) and central-eastern China (e.g., Zheng et al 2013). These systems produce a considerable portion of the warm-season precipitation (e.g., Wallace 1975;Bentley and Mote 1998;Yu et al 2007;Chen et al 2010) and pose a great threat to public safety and property, with hailstorms, flooding, and even tornadoes occurring (e.g., Wilson et al 2018;Trier et al 2006;Kis and Straka 2010). Nocturnal MCSs are often associated with elevated convection initiation (CI) (e.g., Colman 1990;Weckwerth et al 2004;Geerts et al 2017;Reif and Bluestein 2017), where the source of the convective updraft originates above the stable nocturnal planetary boundary layer (PBL).…”

Nocturnal Convection Initiation during PECAN 2015

“…In addition to the SBL, a second feature important for understanding both the initiation and maintenance of nocturnal convection in the Great Plains is the low-level jet (LLJ; e.g., Pitchford and London 1962;Maddox 1983;Astling et al 1985;Trier and Parsons 1993;Trier et al 2006;Tuttle and Davis 2006). The LLJ is a relatively shallow wind speed maximum that occurs between 300 and 1000 m above ground level (AGL), appearing shortly after sunset in the warm season and reaching maximum intensity between 0600 and 0800 UTC (e.g., Blackadar 1957;Bonner 1968;Mitchell et al 1995;Song et al 2005;Shapiro et al 2016).…”

An Evaluation of the Impact of Assimilating AERI Retrievals, Kinematic Profilers, Rawinsondes, and Surface Observations on a Forecast of a Nocturnal Convection Initiation Event during the PECAN Field Campaign

“…We choose to also assimilate PECAN observations on the outer, mesoscale domain with the same cycling configuration as the conventional observations. This is because elevated moist layers, which occur on the mesoscale and are often associated with nocturnal CI (Wilson et al 2018), could likely be improved by assimilating the thermodynamic profilers located at the FP sites. After 2100 UTC, the inner domain is initialized within the outer domain and conventional, PECAN, and level-2 Weather Surveillance Radar-1988 Doppler (WSR-88D) observations are assimilated at 10-min cycling intervals from 2110 UTC 25 June to 0000 UTC 26 June.…”