As a vigorous complex of thunderstorms barreled southeast through central and southern Wisconsin Thursday morning, it was fronted by a menacing, wicked-looking cloud formation.
Shelf clouds form from cold air or outflow racing out ahead of the storm, which sinks and clashes with warm, moist air feeding into it. The humid air rises quickly through this cold layer and condenses into a horizontal cloud resembling a shelf. Sometimes, this happens in multiple layers resulting in a stunning shelf deck resembling a massive flying saucer or “mothership.”
As a shelf cloud arrives, there is usually a sudden burst of heavy rain and strong winds. Then the intensity of the storm tends to ease.
The thunderstorm complex formed ahead of a cold front pushing southward through the Great Lakes toward northern Illinois, Indiana and Ohio. In this vicinity, the National Weather Service has outlined a slight risk zone for severe thunderstorms through Thursday evening.
See more stunning views of the shelf clouds associated with these storms below...
Even with some clutter, what structure! So unusual for us to get such clear definition here in southern Wisconsin.— Kyle Griffin (@kgriffin0) May 16, 2019
Rain just beginning in earnest now, about 10 minutes after this passed. Not much wind either, some gusts to ~30. @NWSMKX #wiwx pic.twitter.com/7au0yl9pEm
More shelf clouds: