资源环境科技发展态势分析平台

Snow rollers have been spotted over the weekend in Wiltshire - https://www.bbc.co.uk/news/uk-england-wiltshire-47108382?SThisFB.

Snow rollers are snow balls formed naturally by strong winds blowing across a flat, snow-covered field or hillside. Three conditions need to occur for snow rollers to form:

• The ground must be icy or covered with a snow crust
• Winds must be strong and gusty
• Snowfall must be wet and at least a couple of inches deep

Once a snow roller is formed the wind gets it to roll, collecting snow as it moves, in some cases even creating tracks of bare ground. The appearance of a snow roller resembles a scaled down version of large rolled hay bales made of snow. Conditions need to be just right for this rare phenomenon to occur. If the wind is too strong or weak these peculiar shapes will not form. The snow roller keeps rolling until it becomes too large or the slope of the ground increases too much for the wind to propel it further. They can vary in size and can get be as large as 1.5 m in length.