If you happened to check the weather radar out of Aberdeen, South Dakota before sunrise last Wednesday (who didn't?), you saw an incredible and unusual sight: a small, spiraling cyclone of snow racing southeast. The swirl almost looks like a small tropical cyclone, with an eye and everything. Here's a look at how the impressive feature formed.
As a weak little wave of energy in the atmosphere moved through the region, it created a bit of a swirl in the radar echos. In reality, these types of features look more ominous than anything, but they can lead to a bit of an enhancement in snow as they pass through if they remain intact.
Here's a look at the circulation using multiple altitude sweeps of the radar, showing the swirl around 4,000 feet above ground level as it passes the radar site and heads southeast.
...and here's a 3D view, just because it's cool looking:
The enhanced band of snow on the west side of the circulation likely produced a quick inch of snow when it passed over mostly rural areas of South Dakota.
[Images: Gibson Ridge's GR2A]