Drop whatever you're doing, make this full screen, turn up the volume, and prepare to collect your jaw off the floor: This is quite simply the clearest and most stunning time-lapse footage of growing supercell storm systems I have ever seen.
Yegads. I actually got chills watching that. Photographer Stephen Locke caught these monsters forming over (yes, seriously) Climax, Kansas, on May 10, 2014. His location and framing are perfect. In almost every shot, the motion of the huge anvil forming at the top is accented by the more rapidly spinning mesocyclone, the massively rotating column of air at the bottom. The mesocyclone walls are exquisite, perfectly formed. Classic and textbook. I love the aquamarine/green hue to the sky in some of the shots; this is a well-known but not completely understood phenomenon.
A supercell is a rotating thundercloud; the spinning vortex in the middle is called a mesocyclone. Conditions need to be just so to create one. First you need a wind shear, where wind blows faster in one spot than another, so a blanket of air is flowing over another one. This sets up a rolling vortex, a horizontally rotating mass of air like the way a wave breaks when it gets to a beach. An updraft then lifts that vortex, which then spins vertically.
The warmer air in the vortex rises; this is called convection. If there’s a boundary layer of air above it, called a capping layer, it acts like a lid, preventing the vortex air from rising. It builds up power and can suddenly and explosively grow to a huge size. Wikipedia has a good description and diagrams of how this works.
I would love to see one of these myself someday ... form a healthy distance. But then, that's how you get the full effect. We do get interesting weather here in Boulder, Colorado, but (perhaps thankfully) not this interesting.
Locke has a gallery of photographs of storms he's shot over the years, and it's truly magnificent.
Tip o' the tornado shelter hatch to Elise Andrew at IFLS.