What is an ACE index – Accumulated Cyclone Energy?

ace index accumulated cyclone energy

The Accumulated Cyclone Energy – the ACE index – is a metric that is used to express the energy used by a tropical cyclone during its lifetime. The calculation takes a tropical cyclone’s maximum sustained winds every six hours and multiplies it by itself to generate the values. The total sum of these values is … Read more

The highest ever measured thunderstorms

highest thunderstorms

How high into the sky can thunderstorms develop – what are the highest even measured thunderstorms? The strongest updrafts reach the tropopause and produce overshooting tops. The highest storms in the world have been recorded in the tropics, where the tropopause is the highest (15-18 km). Thunderstorms reaching 20-22 km high have been recorded there. … Read more

Mammatus clouds

mammatus clouds

Mammatus clouds form on the underside of a thunderstorm’s anvil. Their name comes from the Latin word mamma, meaning “udder” or “breast”. They appear as pouch-like structures protruding from underneath the anvil. Mammatus clouds are gentle downdrafts – sinking cool air – descending from the anvil, that form, evolve, and dissipate over a time span … Read more

Back-sheared anvil – updraft strength vs. wind shear

back-sheared anvil

A back-sheared anvil is the expression for a cumulonimbus anvil that spreads against (upwind) into relatively strong winds (jet stream) aloft. Anvil vs. wind As the anvil is forming, it is under the influence of upper-level winds. Typically as you go higher in the troposphere, winds increase. Under stable conditions with high pressure, winds in … Read more

Overshooting top

overshooting top

Overshooting tops develop on thunderstorms that have particularly strong updrafts. Overshooting tops typically develop on Cumulonimbus capillatus incus clouds. The updraft punches through the equilibrium level (and thus the anvil), rising higher due to its momentum, despite not being buoyant anymore. An overshooting top is usually short-lived, several tens of seconds, up to several minutes. … Read more


typical thunderstorm

In this section, we are going to take a general look at thunderstorms. What is a typical thunderstorm? We will take a thunderstorm apart into its basic components and how they make the thunderstorm work. Typical thunderstorm – Cumulonimbus capillatus incus   The most distinctive and typical cloud shape associated with thunderstorms is Cumulonimbus capillatus … Read more

Types of convective clouds – from fair-weather clouds to thunderstorms

convective cloud types

Convection forms distinct types of clouds. Convective clouds are divided into two types (genera): cumulus and cumulonimbus. Each successive type and species display more vertical development as a result of more convective energy being available. The more convective energy is available, the higher the convective cloud will reach. In terms of how high convection goes, … Read more

Convective initiation – how thunderstorms start

convective initiation

Initiation of convection   On a warm day, convection begins when the air close to the surface warms enough to become buoyant and start rising. This process is called free convection. The temperature at which free convection begins is called the convective temperature. When the convective temperature is reached on a clear, hot, and humid … Read more

Atmospheric instability


Atmospheric instability is a condition where the Earth’s atmosphere is generally considered to be unstable. As air near the ground heats, it becomes more and more unstable and becomes more and more likely to rise convectively. We now take a look at when the atmosphere is stable, less stable, and unstable, what that actually means, … Read more