Severe Thunderstorms – Associated Hazards


Hazardous weather conditions can be packed into very concentrated zones in and around thunderstorms. Hazards include high winds, straight-line winds, large hail, icing, lightning, tornadoes, heavy rain and poor visibility.

A thunderstorm affects a relatively small area when compared to a hurricane or a winter storm. The typical thunderstorm is 15 miles in diameter and lasts an average of 30 minutes. Despite their small size, ALL thunderstorms are dangerous! Below are the many hazardous weather events are associated with thunderstorms:[1]

Lightning is a giant spark of electricity in the atmosphere between clouds, the air, or the ground. In the early stages of development, air acts as an insulator between the positive and negative charges in the cloud and between the cloud and the ground. When the opposite charges builds up enough, this insulating capacity of the air breaks down and there is a rapid discharge of electricity that we know as lightning. The flash of lightning temporarily equalizes the charged regions in the atmosphere until the opposite charges build up again.

Data from the National Lightning Detection Network shows that over the continental U.S. an average of 20,000,000 cloud-to-ground flashes occur every year. Around the world, lightning strikes the ground about 100 times each second, or 8 million times a day.

Lightning causes thunder! Energy from a lightning channel heats the air to around 18,000 degrees Fahrenheit. This causes the air to rapidly expand, creating a sound wave known as thunder. The stepped leader causes the initial tearing sound, and the ground streamer causes the sharp click or crack heard at a very close range, just before the main crash of thunder.[2]

Read more about lightning safety from NOAA.

How Lightning Forms[3]
When the charge difference between the ground and the cloud becomes too large, a conductive channel of air develops between the cloud and the ground, and a small amount of charge (step leader) starts moving toward the ground. When it nears the ground, an upward leader of opposite charge connects with the step leader. At the instant this connection is made, a powerful discharge occurs between the cloud and the ground. We see this discharge as a bright visible flash of lightning.[4]











Wind Damage in Munfordville, KY in 2005[6]

Damaging winds are often called “straight-line” winds to differentiate the damage they cause from tornado damage. Strong thunderstorm winds can come from a number of different processes. Most thunderstorm winds that cause damage at the ground are a result of outflow generated by a thunderstorm downdraft. Damaging winds are classified as those exceeding 50-60 mph.

Damage from severe thunderstorm winds account for half of all severe reports in the lower 48 states and is more common than damage from tornadoes. Wind speeds can reach up to 100 mph and can produce a damage path extending for hundreds of miles.

Since most thunderstorms produce some straight-line winds as a result of outflow generated by the thunderstorm downdraft, anyone living in thunderstorm-prone areas of the world is at risk for experiencing this hazard.

People living in mobile homes are especially at risk from injury and death.  Even anchored mobile homes can be seriously damaged when winds gust over 80 mph.[5]

Flash Flood in Mountain Stream[9]

Flash Flooding Is the #1 cause of deaths associated with thunderstorms with more than 140 fatalities each year. Most flash flood fatalities occur at night and most victims are people who become trapped in automobiles.[7]

Flooding causes more damage in the United States than any other severe weather related event, an average of $5 billion a year. Flooding can occur in any of the 50 states or U.S. territories at any time of the year.[8]



Hail is a form of precipitation that occurs when updrafts in thunderstorms carry raindrops upward into extremely cold areas of the atmosphere where they freeze into balls of ice. Hail can damage aircraft, homes and cars, and can be deadly to livestock and people. How does hail form?

Hailstones grow by colliding with supercooled water drops. Supercooled water will freeze on contact with ice crystals, frozen raindrops, dust or some other nuclei. Thunderstorms that have a strong updraft keep lifting the hailstones up to the top of the cloud where they encounter more supercooled water and continue to grow. The hail falls when the thunderstorm's updraft can no longer support the weight of the ice or the updraft weakens. The stronger the updraft the larger the hailstone can grow.[10]

Table. Hail Diameter Sizes and Updraft Speeds
Hail size is estimated by comparing it to a known object. Most hail storms are made up of a mix of sizes, and only the very largest hail stones pose serious risk to people caught in the open.[11]

Hail size Measurement (in) Updraft Speed (mph)
pea 0.25 40
penny 0.75 44
quarter* 1.00 49
half dollar 1 1⁄4 54
walnut 1 1⁄2 60
golf ball 1 3⁄4 64
hen egg† 2.00 69
tennis ball 2 1⁄2 77
baseball 2 3⁄4 81
tea cup 3 84
grapefruit 4 98
softball 4 1⁄2 103

* Begins hail sizes within the severe hail criterion.
† Begins hail sizes within the Storm Prediction Center's significant severe criterion.

Tornado Touchdown[13]

Spawned from powerful thunderstorms, tornadoes can cause fatalities and devastate a neighborhood in seconds. A tornado appears as a rotating, funnel-shaped cloud that extends from a thunderstorm to the ground with whirling winds that can reach 300 miles per hour. Damage paths can be in excess of one mile wide and 50 miles long. Every state is at some risk from this hazard.[12]






  1. NOAA – National Severe Storms Laboratory – Severe Weather Basics – Lightning Basics:
  2. NOAA – National Severe Storms Laboratory – Severe Weather Basics – Lightning Basics:
  3. Image Source: [Accessed March 23, 2014]
  4. NOAA – Thunderstorms, Tornadoes, Lightning…A Preparedness Guide –
  5. NOAA – National Severe Storms Laboratory – Severe Weather 101 – Damaging Winds:
  6. Image Source: [Accessed March 23, 2014]
  7. NOAA Watch – Severe Weather:
  8. NOAA – National Severe Storms Laboratory – Severe Weather 101 – FAQs About Floods:
  9. Image Source: [Accessed March 23, 2014]
  10. NOAA – National Severe Storms Laboratory – Severe Weather 101 – Hail Basics:
  11. NWS – National Weather Service Forecast Office – Marquette, MI:
  12. – Tornadoes:
  13. Image Source: [Accessed March 23, 2014]