All thunderstorms are dangerous. Every thunderstorm produces lightning. Lightning continues to be one of the top three storm-related killers in the United States. Thunderstorms can generally form and develop in any geographic location, perhaps most frequently within areas located at mid-latitude when warm moist air collides with cooler air. Thunderstorms are responsible for the development and formation of many severe weather phenomena. Thunderstorms, and the phenomena that occur along with them, pose great hazards to populations and landscapes. Damage that results from thunderstorms is mainly inflicted by downburst winds, large hailstones, and flash flooding caused by heavy precipitation. Flash flooding is responsible for more fatalities than any other thunderstorm associated hazard. Stronger thunderstorm cells are capable of producing tornadoes and waterspouts. Dry thunderstorms that do not produce rain that reaches the ground can start wildfires.
Lightning often strikes outside of heavy rain and may occur as far as 10 miles away from any rainfall. Heat lightning is actually lightning from a thunderstorm too far away from thunder to be heard. However, the storm may be moving in your direction.
Terminology
- Severe Thunderstorm Watch - Tells you when and where severe thunderstorms are likely to occur. Watch the sky and stay tuned to NOAA Weather Radio, commercial radio or television for information.
- Severe Thunderstorm Warning - Issued when severe weather has been reported by spotters or indicated by radar. Warnings indicate imminent danger to life and property to those in the path of the storm.
- Downburst - A downburst is created by a column of sinking air that, after hitting ground level, spreads out in all directions and is capable of producing damaging straight-line winds of over 150 mph.
- Bow Echo - A bow echo is a term describing the characteristic radar return that is shaped like an archer's bow. These systems can produce severe straight line winds and occasionally tornadoes, causing major damage.
Classifications
- Single Cell - This term technically applies to a single thunderstorm with one main updraft. Also known as air-mass thunderstorms, these are the typical summer thunderstorms in many temperate locales.
- Multicell Clusters - This is the most common type of thunderstorm development. Mature thunderstorms are found near the center of the cluster, while dissipating thunderstorms exist on their downwind side. Multicell storms form as clusters of storms but may then evolve into one or more squall lines.
- Squall Line - Is an elongated line of severe thunderstorms that can form along and/or ahead of a cold front. The squall line contains heavy precipitation, hail, frequent lightning, strong straight line winds, and possibly tornadoes and waterspouts. Severe weather in the form of strong straight-line winds can be expected in areas where the squall line itself is in the shape of a bow echo, within the portion of the line that bows out the most.
- Supercells - The most powerful type of thunderstorm, with wind speed and direction that vary with height ("wind shear"). These storms normally have such powerful updrafts that the top of the cloud (or anvil) can reach into the lower levels of the stratosphere and can be 15 miles wide. At least 90 percent of this type of thunderstorm bring severe weather. These storms can produce destructive tornadoes, sometimes F3 or higher, extremely large hailstones (4 inches diameter), straight-line winds in excess of 80 mph, and flash floods. In fact, most tornadoes occur from this type of thunderstorm.