A Localized Lake Effect Cloud Formation

February 07, 2018



Photographer: Raymond Murphy 
Summary Author: Raymond Murphy 

The photo at tops shows a localized lake-effect cloud bank that has formed over the Montreal borough of Lachine, about 6 mi (10 km) to the east. It was taken from a lakeside park in Pointe Claire, Quebec on December 31, 2017. On the day the photo was snapped, the air temperature was -4 F (-20 C), and it had been bitterly cold for several days in a row.

The cloud is at the eastern end of Lake Saint-Louis, a lake in the St. Lawrence River that lies directly south of the western part of the island of Montreal. It's approximately 12 mi (20 km) long and 6 mi (10 km) wide. Most of the northern side of the river was frozen over, but the southern side was still unfrozen for most of its length. A strong prevailing wind was aligned with this open water. Lake-effect weather is generated when cold air moves across warmer open water, transferring moisture and resulting in frequent, and sometimes heavy, snowfalls on the windward shores of the Great Lakes.

The bottom photo, taken in Lachine at a point a little downwind of the center of the cloud-formation activity, shows the lake-effect cloud aloft, as well as the thick freezing fog on the open water. This fog contributed to an accumulation of rime on the trees and shrubs at places near the water’s edge. However, there was no apparent precipitation aside from that produced by the fog.

Photo Details: Top - Camera: Canon EOS 7D; Exposure Time: 0.0010s (1/1000); Aperture: ƒ/10.0; ISO equivalent: 160; Focal Length: 35.0mm; Software: Digital Photo Professional. Bottom - same except: Exposure Time: 0.0016s (1/640); Aperture: ƒ/10.0.