Supercells are what storm chasers are after each and every year. Ask any storm chaser what they’re really after out there and it is probably either tornadoes or incredible storm structure — both of those are most common with supercells! These rotating storms pack a punch, creating some of the most dangerous weather on earth while being the primary manufacturers of tornadoes.
If you are new to severe weather, weather, climate, or really anything to do with all of this genre of content — you may be wondering about how these supercell storms form, where they form, what the different types are, and (of course) how they churn out twisters. Here is a brief introductory primer on these monster supercells. In this video we talk about what supercells are, how supercells form, the different types of supercells, and how tornadoes are born from supercells.
What are the ingredients for supercells to form?
The ingredients required to come together to create these storms are similar parts miraculous and devastating. To create a supercell, you need the ultimate atmospheric recipe.
The first ingredient you need is warm and humid air in place at the surface with colder and drier air aloft. This is atmospheric instability and you need this for storm clouds to rise up into the atmosphere. [See more on CAPE]
But what causes storms to rise in the first place? That’s lift. You can get lift from many sources, from surface boundaries like fronts or the dryline, to warm air advection, and to upslope flow. Lift is usually maximized near clashing air masses, but you can also get lift from other processes as well.
If you have both instability and lift, the final crucial ingredient still needs to be in place. For supercells to form, you need ample wind shear. But what you really need is a special type of wind shear, with winds from the south or southeast at the surface turning to the west aloft with increasing wind speeds as you go up. This helps create and maintain the mesocyclones that all supercells possess. [See more on Wind Shear]
When you mix all three together: instability, lift, and wind shear — you get an environment ripe for the tornado factories known as supercells.
Not all supercells are created equal. In fact, there are three main types of supercells that you will commonly see.
The first is the high precipitation supercell. These monster storms have the lowest levels of the mesocyclone obscured by rain. These are dangerous storms to document, with the tornado oftentimes hidden behind a wall of rain.
Another type of supercell is a favorite of mine, the low-precipitation supercell. These storms are typically the exact opposite of the HP, with sometimes seemingly no precipitation falling at all. Tornadoes with these types of supercells are more rare. But beware, driving near these spinning storm clouds could result in you encountering giant hail.
The ideal tornado factory though is the classic supercell. As you might have guessed, these are a middle ground between the HP and LP storms. Classic supercells are examples of supercells perfectly in balance. The low-level mesocyclone isn’t too waterlogged but there is enough of a storm core to set in motion the processes you’d look for to get a tornado to form. Many of the most notorious tornadoes in history have come from classic supercells.
Why Supercells Are So Good At Churning Out Tornadoes
But why are supercells so good at producing tornadoes anyways? Let’s look at how these factories churn out twisters.
Tornadoes form in environments with both lower cloud bases thanks to higher humidity near the surface and stronger low-level wind shear. Both of these, along with my preferred isolated storm modes, are the ingredients I look for to choose which chase days to pursue each Spring.
After a supercell has formed, the manufacturing process begins immediately to produce a tornado. Storms that are by themselves, or isolated, stand the best chance to manufacture a tornado. This is because the processes that go into producing tornadoes are very fickle. Disturbances from other storms can jam up the gears, putting the entire process on hold.
The Tornado Manufacturing Process
The first stop on the assembly line is the storm pulling in the rich and unstable air into its updraft. The updraft is the visible cloud of the storm. This is called inflow, and you’ll hear storm chasers talk about this being the first sign a tornado could be coming.
Once a storm is pulling in sufficient inflow, another process begins to take shape on the back side of the storm: the rear flank downdraft. This piece of the process is a unique component of the supercell. It likely plays a key role in the formation of a tornado. Science hasn’t quite settled why, but there are some clues.
As the rear flank downdraft descends and wraps around the southern end of the mesocyclone and then around to the east side, this helps focus the rotation in a smaller area and smaller area while lowering the pressure underneath the updraft. As the spin of this feature increases and deepens, a funnel may become visible and start reaching towards the surface. Eventually, you will see signs of ground contact as this process plays out. When you see this, you know the tornado factory has done it again.