Snow devils are natural phenomena characterized by a swirling column of snow. They appear as rotating pillars of snow, extending upward from a snow-covered surface. While sharing a visual resemblance to dust devils, snow devils emerge under specific winter atmospheric conditions.
The Science Behind Their Formation
Snow devils develop from atmospheric and surface conditions, operating as a type of vortex similar to a dust devil. Their formation begins when a warmer ground surface, such as dark asphalt or bare earth, exists beneath a layer of colder air. Direct sunlight can warm these surfaces, even when ambient air temperatures are cold. As the surface warms, it heats the air directly above it, causing this warmer, less dense air to rise.
This rising warm air creates an updraft. When this updraft encounters descending cooler air, it can initiate a rotating column. Wind shear, which is the change in wind speed or direction with height, also plays a role in generating the rotational motion. The combination of convection and wind shear allows the vortex to form and pick up loose, dry snow from the ground. Snow devils require precise conditions, including the presence of dry, uncompacted snow, to become visible.
Key Features and Visuals
Once formed, a snow devil is a spinning column of snow. Its height can vary, ranging from a few feet to tens of feet. Many observed snow devils average between 12 to 15 meters (40 to 50 feet) in height, with diameters between 4.5 to 9 meters (15 to 30 feet). Some can even reach over 10 meters (33 feet) in both height and diameter.
These swirling columns are transient, lasting for only a short period. Their lifespan ranges from 30 seconds to two minutes before dissipating. The rotational direction of a snow devil can be either clockwise or counter-clockwise, influenced by factors like the local temperature gradient and the direction of wind shear. Despite their appearance, they are light columns of snow that do not pose a hazard.
Common Environments for Observation
Snow devils are observed in specific settings where atmospheric and surface conditions align. They appear in large, open, snow-covered areas such as frozen lakes, expansive fields, or paved surfaces like parking lots and roads. The presence of fresh, loose, and dry snow is a prerequisite for these phenomena to become visible.
The weather conditions conducive to their formation include clear, sunny skies following a snowfall. This allows solar radiation to reach and warm the ground surface, creating the temperature difference needed for convection, even if the air above remains cold. These conditions contribute to their rarity.