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Old 01-11-2010, 11:53 AM   #1
Potemkin
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Default Snow "Tumbleweeds"

http://www.dailymail.co.uk/news/arti...henomenon.htmlBig freeze gives rise to rarest frosty phenomenon: a snow pipe



By Neil Millard
Last updated at 9:24 AM on 11th January 2010

It looks like the work of aliens, late-night pranksters or an as yet undiscovered animal building a nest.


But this strange-looking snow formation has a very natural explanation.
'Snow rolls' are cylinders of snow found in freezing conditions on open ground and most commonly appear on the prairies of North America.
Also known as snowrollers, snow bales and snow doughnuts, the phenomenon requires a precise balance of air temperature, ice, snow, moisture and wind. They are essentially a wintry version of tumbleweed.





Totally natural: An example of the giant self-rolling snow rolls pictured by dog walker Ron Trevett

Builder Ron Trevett, 55, and his wife Aileen, 54, were amazed to find them in a field near their home in Yeovil, Somerset, as they walked their dogs.
'We saw them from a distance on the ridge of the field, and we thought some kids had been playing up there and making giant snowballs,' said Mr Trevett.

'But when we got up there we saw there were no footprints and there were hundreds of them, too many for children to have done it. We realised it must have been the wind.'

The couple considered themselves privileged to have had the chance to see them.

'We feel very lucky. I'm the wrong side of fifty and I've never seen anything like it in my life.


Dozens of snow rolls were found scattered across this Somerset field

'We were gobsmacked to look at them there in the sunlight. It was a really impressive sight and I took some pictures so other people could share it.'
Frank Barrow, a lecturer in meteorology at the Met Office, described the exact science behind the formations and said it was nature's version of a snowman.
He said: 'They start off with a nice thick layer of snow, with the top snow just on the point of melting either because of general temperature or sunshine on the surface.
'The top snow layer becomes a bit sticky and you then need a fairly strong wind. The sticky layer can be peeled off the colder and more powdery snow underneath by the wind, forming a roll.

'In the first picture you can see some of the powdery stuff sticking to the lower outside surface of the roll. I suppose it is a natural version of making a snowman.'
The rolls are not hollow to begin with, as a number of layers build up as the roll gets larger the further it is blown.

However, the inner layers are weaker as they are formed first and are easily blown away. Eventually the rolls become too big to be blown any further or come to rest against vegetation or at the bottom of a hill.

Liz Bentley, from the Royal Meteorological Society, said despite their rarity more snow rolls could appear in the UK in the coming days.
'These rolls are unusual here because we don't tend to have major snow events like the one we're experiencing now.

'They happen with the combination of lying snow and high wind speeds, mostly in North America and Northern Europe, and they can be as small as a tennis ball or they can be as large as two feet across – depending on how strong the wind is and how smooth the surface of the snow is,' she said.
'There are quite strong winds predicted this weekend as well as more snow, so if people keep a look out they might see a few more of these appearing around the country over the next few days.'

Read more: http://www.dailymail.co.uk/news/arti...#ixzz0cJs5RVJz
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