A Severe Thunderstorm Outbreak North of 70°N Over the Canadian Arctic Islands with Unusual Lightning Characteristics

Abstract

ABSTRACT This study explores the causes of a severe thunderstorm outbreak north of 70°N on 24–25 July 2014 and provides the first characterization of lightning over the Canadian Arctic Islands. Lightning data were obtained from the Global Lightning Dataset (GLD360) network. Convective available potential energy calculated using representative soundings and surface conditions indicated high instability that, combined with large vertical wind shear and storm-relative helicity, likely caused severe thunderstorms to form over Victoria Island. These storms subsequently drifted northeastward over Parry Channel, where they transitioned into elevated storms and travelled as far north as and passed close to Grise Fiord (76.4°N). Satellite imagery suggested that overshooting tops reached 11.6 km. The GLD360 network detected more than 15,000 strokes north of the Arctic Circle and an unusually high ratio of positive strokes during this outbreak.