Gust front collision: 2 July 2010

Introduction

Low-level convergence is commonly enhanced along thunderstorm gust fronts. This convergence can be further increased by interactions between gust fronts. Under suitable vertical stratifications of moisture and instability, gust front-related convergence can initiate the development showers and thunderstorms. During the afternoon of 2 July 2010, the CSU-CHILL radar was making low elevation PPI scans at time intervals of ~ 4 minutes. While these scans were in progress, the collision of two gust fronts was observed. Following this collision, a thunderstorm developed in the immediate vicinity of Denver International Airport.

Reflectivity loop

Reflectivity "fine lines" marked the locations of the two gust interacting gust fronts. Convergence along these gust fronts locally collects the insects that are present in the undisturbed boundary layer. The increased insect concentrations result in a stronger radar reflectivity level.

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Radial velocity loop

Converging radial velocity patterns were commonly present along the fine lines; especially in the vicinity of the collision area.

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Differential Reflectivity Loop

Differential reflectivity values are quite positive (> ~+5 dB) in the insect echo regions. This is due to the highly oblate body shapes that insects typically present. A pulse of positive Zdr values can also be seen during the intense phase of the thunderstorm over KDEN.

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