Know the Lingo: Severe Storms and Tornadoes

Preparing For a Heatwave

Severe Storms Terminology


A supercell is a thunderstorm that is characterized by the presence of a mesocyclone: a deep, persistently rotating updraft. Supercells are typically also classified as severe thunderstorms, and tornadoes most commonly form from these kinds of storms.

Severe Thunderstorm

A very strong thunderstorm in which at least one of the following is present:

  • Hail 3/4 of an inch or greater
  • Winds greater than 58 mph
  • A tornado

A rotating column of air that stretches from the base of a thunderstorm. Upon impact with the ground, strong winds associated with a tornado can kick up dust and debris, and cause great damage.

Straight-line Winds

Strong winds that aren't associated with a tornado, but cause considerable damage.


A frozen form of precipitation consisting of individual balls or lumps of ice called hail stones, produced from cumulonimbus or thunderstorm clouds. A bigger hail stone signifies a longer lifespan within the cloud, which also signifies a strong thunderstorm with strong updrafts. Hail can cause significant damage.

Watches, Warnings, and Advisories

Severe Thunderstorm Watch

A severe thunderstorm watch is issued when there is a possibility that thunderstorms in and near the watch box area may produce the following severe weather conditions:

  • Hail 3/4 of an inch or greater
  • Winds greater than 58 mph
Severe Thunderstorm Warning

A severe thunderstorm warning is issued when a storm with any of these severe weather criteria is approaching the warning area:

  • Hail 3/4 of an inch or greater
  • Winds greater than 58 mph

Severe thunderstorms can and do produce tornadoes.

Tornado Watch

Tornadoes are possible. Remain alert for approaching storms. Watch the sky and stay tuned to NOAA Weather Radio, commercial radio or television for information.

Tornado Warning

A tornado has been sighted or indicated by weather radar. Take shelter immediately.

Enhanced Fujita Scale

Dr. T. Theodore Fujita developed the Fujita Tornado Damage Scale (F-Scale) to provide estimates of tornado strength based on damage surveys. Since it's practically impossible to make direct measurements of tornado winds, an estimate of the winds based on damage is the best way to classify a tornado. The new Enhanced Fujita Scale (EF-Scale) addresses some of the limitations identified by meteorologists and engineers since the introduction of the Fujita Scale in 1971. The new scale identifies 28 different free standing structures most affected by tornadoes taking into account construction quality and maintenance. The range of tornado intensities remains as before, zero to five, with 'EF-0' being the weakest, associated with very little damage and 'EF-5' representing complete destruction, which was the case in Greensburg, Kansas on May 4th, 2007, the first tornado classified as 'EF-5'. The EF scale was adopted on February 1, 2007.

Rating Typical Damage:
EF-0 (65-85 mph) Light damage. Peels surface off some roofs; some damage to gutters or siding; branches broken off trees; shallow-rooted trees pushed over.
EF-1 (86-110 mph) Moderate damage. Roofs severely stripped; mobile homes overturned or badly damaged; loss of exterior doors; windows and other glass broken.
EF-2 (111-135 mph) Considerable damage. Roofs torn off well-constructed houses; foundations of frame homes shifted; mobile homes completely destroyed; large trees snapped or uprooted; light-object missiles generated; cars lifted off ground.
EF-3 (136-165 mph) Severe damage. Entire stories of well-constructed houses destroyed; severe damage to large buildings such as shopping malls; trains overturned; trees debarked; heavy cars lifted off the ground and thrown; structures with weak foundations blown away some distance.
EF-4 (166-200 mph) Devastating damage. Whole frame houses Well-constructed houses and whole frame houses completely leveled; cars thrown and small missiles generated.
EF-5 (>200 mph) Incredible damage. Strong frame houses leveled off foundations and swept away; automobile-sized missiles fly through the air in excess of 100 m (109 yd); high-rise buildings have significant structural deformation; incredible phenomena will occur.

Some content from:

Prepare For the Extreme

By the time severe weather hits, it's already too late. Disaster preparedness is about having an established safety plan. Whether it's preparedness for floods, earthquakes, hurricanes, or fires, the key to survival in disasters is planning. Use our preparedness section to stay informed, make a plan, and most importantly—remain safe in an emergency.