A supercell is a thunderstorm with a deep, persistently rotating updraft.
Supercells are the least common form of thunderstorm yet they are potentially the most violent. Large hail of greater than baseball size, strong damaging winds, and tornadoes can accompany these storms.
To storm chasers, Supercells are the grand catch — they are the bounty which storm chasers most commonly hunt for.
What are the Parts of a Supercell?
Supercells are made up of several different parts. At the most basic level, a supercell features a deep/rotating updraft and a strong downdraft. An updraft is where warm and moist air rises and condenses within the storm and thanks to strong wind shear, the updraft and the downdraft are typically in different places — which allows the storm to thrive as it can ‘breathe’.
Underneath the updraft at it’s strongest point is oftentimes a wall cloud. A persistent and rotating wall cloud indicates the potential for tornado formation and should always be watched closely.
What are the types of supercells?
There are three main types of supercells.
- Classic Supercells – The rear flank downdraft (RFD) oftentimes is pretty strong but doesn’t have much precip, which results in the updraft and updraft base being visible next to a heavy and opaque downdraft/storm core.These are the storms which most commonly produce the most tornadoes, as the RFD isn’t so strong as to overwhelm the storms updraft/area of rotation.
- HP Supercells – These storms are a nightmare to chase as the RFD is strong and wet, which results in much of the updraft base being obscured in heavy rain. When a storm is HP, tornadoes are oftentimes buried in rain and invisible as they approach. The cores on these storms can oftentimes look incredibly mean as heavy rain and hail accompany them.
- LP Supercells – LP supercells are almost always incredibly beautiful. They often feature weak RFDs and the downdrafts/hail cores and oftentimes be transparent. These storms are oftentimes big hail producers and can sometimes produce spectacular and photogenic tornadoes. To a storm chaser, an LP supercell is an amazing catch. They are most common in the high plains of the US.
How do supercells form?
A supercell requires several very unique factors coming together in order to see them form. All thunderstorms require three ingredients to form: moisture, instability, and lift.
Supercells, on the other hand, require all three of those plus an additional factor: wind shear.
- Moisture: Supercells require adequate moisture to be present in order to form. On the Plains, the base line for good supercell thunderstorms is usually 50F. For supercells to be tornadic, the base line figures are usually dewpoints of 55F on the High Plains and 60F for the lower plains. These vary setup to setup though.
- Instability and Lift: Unstable air is air that tends to rise when it is lifted. For air to rise, it has to be hotter than the air surrounding it, think about the old saying ‘hot air rises’. That saying is true for the atmosphere as well. Unstable air occurs when the air at the surface is warmed beneath cooler temps aloft. The faster the air tends to rise, the more unstable the atmosphere is.
- Wind Shear: Supercells need to have the updraft rotating, this is accomplished through wind shear or wind which veers (turns westward) and speeds up with height. This wind shear creates horizontal vorticity which is then titled upwards by a strong thunderstorm updraft, creating the deep/rotating updraft supercells require.