Strange Weather Occurrence in Nova Scotia April 28, 2009

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http://www.novanewsnow.com/article-331480-Environment-Canada-explains-strange-weather-phenomena.html
http://www.novanewsnow.com/article-331480-Environment-Canada-explains-strange-weather-phenomena.html#photos

Environment Canada explains strange weather phenomena
 by Carla Allen/The Vanguard

Article online since April 29th 2009, 13:46
 
What many Yarmouth County residents saw in the sky Tuesday evening, April 28. Photo by Stephen Sollows  View all pictures Environment Canada explains strange weather phenomena
By Carla Allen

NovaNewsNow.com

Meterologists at Environment Canada are all abuzz about an ominous, dark, fast moving cloud that passed over much of Yarmouth County between 7 and 9 p.m. on April 28.

Meterologist Serge Deschamps says the cloud seems to be what is known as a roll cloud. The report created quite a stir in the office.

“It is very rare phenomena. All the right conditions have to be set up and I guess you had it set up yesterday,” he said.

“Everybody has heard about it and studied it, but never actually saw it or experienced it,” he said.

When the tephigram for the Yarmouth area was examined after the cloud’s passage, the anomaly was confirmed.

A tephigram provides a 3D picture of the upper atmosphere, providing temperature, humidity and winds.

A dramatic inversion took place at the time, with colder air near the surface, and warm air in the layer above. Meterologists refer to the event as “very stable”

“The roll cloud was right ahead of a cold front that was sweeping down across Nova Scotia. Greenwood went from 26 to 16 degrees in one hour,” said Deschamps.

The cloud is also known as a morning glory cloud because it is observed most often during spring near dawn. It is considered one of the world's most exotic meteorological phenomena and is best known from the Gulf of Carpentaria, northern Australia.

The clouds appear as one or more roll cloud formations extending from horizon to horizon, and sometimes measure more than 1,000 km in length, travelling 1 - 2 km. above the earth’s surface.

Despite being studied extensively, the Morning Glory cloud is not clearly understood. The clouds seldom produce measurable precipitation but are almost always accompanied by short-lived, often intense, surface wind squalls, intense low-level wind shear, and a sharp pressure jump at the surface.

In the front of the cloud, there is strong vertical motion that transports air up through the cloud to create a rolling appearance. Air in the middle and rear of the cloud becomes turbulent and sinks. They are reported to travel at speeds of about 40 km/hr, occasionally over 60 km/hr.

Burketown, Australia, annually attracts glider pilots bent on riding this phenomenon.

Morning Glory clouds have been sighted three times in 25 years on Sable Island (June 13, 2003; July 8, 2000, and in the summer of 1976.

For more information on Morning Glory clouds and photos,

visit: www.greenhorsesociety.com

People also reported a very quick and hard blowing wind that lasted only a few seconds and then was over further inland.