Supercells

Science 123		Spring 2020
	Supercells

Supercells
- severe thunderstorm with a single rotating updraft with a life-span of several hours
- photo image
- cross-sectional view
- plan view
- radar image
- mesocyclone - rotating updraft with diameters as large as 15 km
  - Twin supercell development - Iowa City storm of April 13, 2006
  - one theory on the development is the spinning vortex tube in an environment of vertical wind shear
  - explanation of hodograph and the development of helicity
- mesocyclone: cyclostrophic flow and vertical pressure gradient

Other Features
- wall cloud - rotating clouds that extend from the initial cloud base
  - formed by condensing moisture in the updraft
  - parcels are cooled by adiabatic expansion while entering the lower pressure mesocyclone
  - eventually, a vortex or funnel cloud may form and extend to the surface - if so, a tornado has formed
- Weak Echo Region (WER)
- Bounded Weak Echo Region (BWER) - the (nearly) precipitation free strong updraft region associated with the mesocyclone
- overshooting top
- forward downdraft
  - rain-cooled air associated with the precipitation
  - relatively cool and moist
- rear flank downdraft
  - air from aloft that collides with the storm and brought down to the surface
  - relatively warm and dry
- gust front

Formation Environment
- synoptic scale features
- large CAPE
- strong, deep vertical wind shear
- sounding