Top Shelf Cloud ...the talk of the county!
Maureen Foster snapped this photo of an ominous shelf cloud from her backyard in Middle Stewiacke NS
Published Tuesday, June 27, 2017 11:58AM ADT
Last Updated Tuesday, June 27, 2017 12:02PM ADT
Yesterday’s blog was about an intriguing and relatively new cloud type that was spotted in our region Friday - the undulatus asperatus. I wouldn’t normally blog about clouds 2 days in a row, but I have to make an exception today.
I’ve been getting so many photos and comments regarding the ominous clouds that billowed over Hants and Colchester counties yesterday morning that I felt like I really should address it.
The cloud was a shelf cloud. A shelf cloud is a low-hanging, well-defined, sometimes wedge-shaped formation that occurs along the leading edge of an intense line of thunderstorm. Shelf clouds most often form in a gust front – a rush of air from the top of the cloud. Cool, sinking air from a storm cloud's downdraft spreads out across the land surface, with the leading edge called a gust front. This outflow cuts under warm air being drawn into the storm's updraft. As the lower cooler air lifts the warm moist air, its water condenses, creating a cloud which often rolls with the different winds above and below. You don’t normally find persistent rotation on a vertical axis with this cloud.
Shelf clouds can be very scary-looking since they are usually low-hanging; they can sit only a couple hundred meters above the ground. There are two other phenomena that might resemble tornadoes or funnel clouds but are not: dark rain shafts and the white color of a hail shaft that could create a light-dark contrast with surrounding rain, resulting in what might appear to be a funnel cloud or a tornado to the untrained eye.
Remember, the presence of a shelf cloud is a sign of some powerful thunderstorms in the area; take shelter and stay safe if you happen to spot one!