Contents:

• Introduction
• Supercells
• Terms associated with Supercells
• Tornado Intensity
• Other Hazards

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Introduction:

The following is an illustrated guide to what types of features are often seen before and during severe weather events. Since supercell thunderstorms produce the majority of severe weather and are common in many parts of the country, this page focuses on this phenomenon.

Caution: Storm spotting is an activity performed only by trained individuals! This page is not meant to be a substitute for official storm spotter training.

Contact your local NWS office for details on spotter training in your area. The NWS does not sponsor storm spotters or storm chasers, but works with them to obtain and provide up to the minute information on severe weather.

Thunderstorms are common in many parts of the U.S., and most area residents are quite familiar with them and the severe weather they can bring. Most individual thunderstorms only last several minutes, however some individual thunderstorms can last several hours. These long-lived thunderstorms are called supercell thunderstorms. Supercell thunderstorms are solely responsible for producing the majority of severe weather, such as large hail and tornadoes, however, strong squall lines can also produce widespread severe weather, primarily very strong winds and/or microbursts.

A supercell thunderstorm, in brief, is a thunderstorm with a persistent rotating updraft. This rotation maintains the energy release of the thunderstorm over a much longer time than typical, pulse-type thunderstorms which occur in the summer months in the U.S. A 3-D visualization of a simulated supercell thunderstorm is shown below. Notice the rotating streamlines around the orange, carrot-shaped object which indicates the location of the rotating updraft.

Tornado - A violently rotating column of air in contact with the ground. A condensation funnel does not need to reach to the ground for a tornado to be present; a debris cloud beneath a thunderstorm is all that is needed to confirm the presence of a tornado, even in the total absence of a condensation funnel. A description of tornado intensity classification is shown below.

LP storm (or LP supercell) - Low-Precipitation storm (or Low-Precipitation supercell). A supercell thunderstorm characterized by a relative lack of visible precipitation. Visually similar to a classic supercell, except without the heavy precipitation core. LP storms often exhibit a striking visual appearance; the main tower often is bell-shaped, with a corkscrew appearance suggesting rotation. They are capable of producing tornadoes and very large hail. Radar identification often is difficult, so visual reports are very important. LP storms almost always occur on or near the dry line, and therefore are sometimes referred to as dry line storms.

Tornado Intensity:

Tornadoes vary in size and destructive potential. The winds of a tornado have only recently been estimated with specialized radars (FM-CW), however up until then, the Fujita Scale or F-Scale has been used to quantify tornadic winds according to the extent of damage to buildings and structures.