The Structure, Evolution, and Dynamics of a Nocturnal Convective System Simulated Using the WRF-ARW Model

Ben Blake
Noon Mar 29 in Room 2155

Previous studies have documented a nocturnal maximum in thunderstorm frequency across the central United States. Forecast skill for nocturnal convection remains relatively low, and the explanation for this nocturnal maximum is still an area of active debate. This study utilized the WRF-ARW model Version 3.6.1 to simulate a nocturnal mesoscale convective system event that occurred over the southern Great Plains on 3-4 June 2013. The purpose of this study was to advance the knowledge of the dynamics, structure, and evolution of nocturnal convection through examining the structure of the simulated storm from the perspective of two dynamical frameworks.

The structure and evolution of the storm was influenced by a strong horizontal gradient in CAPE and CIN corresponding to a narrow corridor of high mixing ratios associated with the low-level jet. These CAPE values in the jet exceeded the magnitude of CAPE observed in the daytime boundary layer. During the night, the source of convectively unstable parcels was almost entirely above 1 km, the storm was elevated with positive buoyancy limited to heights above ~4 km, and the cold pool became stronger aloft than at the surface. Significant variation in the depth and structure of the ascent was found around the cold pool. The reasons for this variation are examined via two frameworks: i) The RKW framework for vertical shear/cold pool interactions; ii) The dynamical framework of wave theory (e.g. Froude number, Scorer parameter). The application of these theories allowed insight into the three-dimensional structure of the convective system and provided a possible explanation for how convection is maintained at night in the presence of a low-level jet.