Shelf Cloud and Squall Line Approaching Syracuse, Italy

December 08, 2021


Photographer: Barbara Pindo

Summary Author: Barbara Pindo; Cadan Cummings

The photo above shows a shelf cloud that formed on the leading side of a squall line, also known as a Groppo line, near the city of Syracuse, Italy. This distinct cloud formation was visible over the city in the afternoon on May 10, 2021 and appeared as a long, narrow band of strong storms that continually regenerated. Squall-line formations can at times be 60 to over 180 miles (100 to 300 km) long and often precede severe weather. These events develop on the separation line between warm, humid air present on the ground, and colder, heavier air in the atmosphere that is being pushed by a cold front. The cold, dry air raises the warm, humid air forming a series of cumulonimbus clouds parallel to the advancing front. At the transition of a Groppo Line, there are several weather conditions that often occur together or in succession. Initially very strong wind-- just as what was experienced in Syracuse-- develops and precedes heavy rain or mixed rain/ hail and an ensuing area of lighter rain from stratiform clouds. Prior to this event, I had not seen this phenomenon before but luckily I was able to capture it in this panoramic photo.

Photo details: Canon Eos 1100D; Focal length 18.00 mm; Exposure 1/200 sec; f/3.5; ISO-200. Five photos combined into a single panoramic photo.

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