Hazardous Weather Education

Severe weather occurs across the United States and around the globe. Learn about flooding, hail, hurricanes, tornadoes, and damaging winds as we take a look inside severe weather.

Severe weather can occur nearly anywhere at anytime. Let's take a look at different forms of severe weather and other hazards. Click on a title and jump to the specific section. Our Project Weather 2.0 initiative also promotes weather alert technology in every home.

Jump to: Flooding | Hail | Lightning | Hurricanes | Tornadoes | Damaging Winds
Introduction: Are You Ready For Severe Weather?
Severe weather season in reality -sometimes- never ends. In fact, severe weather can occur even outside of season. Now is the time to get a plan of action for your family or business. When severe weather strikes you may only have seconds to react. Plan today by preparing for hazardous weather with this free checklist. Even a weak severe storm can cause damage creating power and traffic problems. Make sure you are prepared by knowing what to do. Your first step may be getting a NOAA Weather Radio.

Thunderstorms occur around the world every day of the year. In fact, storms are a normal cycle in the earth-atmospheric exchange system. Chances are you've been in a countless number of average thunderstorms. However, nature can become violent. When atmospheric conditions favor, severe and unusual weather can occur (sometimes with little or no warning). Let's dissect the most common forms of dangerous weather.

Flooding
The most common type of dangerous weather is flooding. Recurring storm activity may increase the chance of flooding in your area as storms produce heavy rain over already saturated grounds. Other factors also increase the chances of flooding such as locations that are low-lying, near any body of water, and especially downstream of dams.

Flooding occurs when rainfall causes a river or stream to overflow and flood the surrounding location. The term flash flood is used when within six hours of a rain event, dam failure, or a sudden transport of water occurs. The National Weather Service calls this a "flash flood warning", flash meaning urgent in nature.

Flooding is a real danger from storms costing over $5 billion dollars damage each year. Two feet of water can harvest enough power to lift and move a vehicle, even a bus. Water less than 1 foot deep if moving swiftly enough can knock a person down. In 1935, the Chinese river Yangtze flooded reportedly causing the death of over 100,000 people. The great Mississippi river flooded in 1927 causing 246 deaths across seven states. In late August 2005, hurricane Katrina over a period of days became the largest flood impacting the United States ever recorded in modern history causing the deaths of over 1,000 people.

Remember that flooding can occur quickly. It's important to pay close attention to forecast information and warnings. If a flood warning is issued for your area, seek higher ground immediately. Rapid flooding can include fast moving water powerful enough to lift cars, houses, and easily overtake any good swimmer. Never cross waters of unknown depth.

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Large Hail
Any storm can produce hail. *The National Weather Service is starting to shift towards a 1" (one inch) hail size as the minimum criteria to issue a warning. Some offices started this policy. Your author believes that eventually and very soon - all offices will change from the pre 2005 hail size of 3/4" to 1" for all United States locations. Severe hail comes in many sizes starting at 1" (in circumference). At this size, The National Weather Service considers the storm to be severe. The strength of the updraft will determine the size of the hail. Stronger thunderstorm updrafts can produce hail as large as basketball in size (recorded in history). At basketball size, hailstones can puncture roofs and floors causing external and internal damage.

Severe hail is extremely dangerous and destructive. Never try to drive in severe hail. Large stones can easily break glass, puncture many surfaces, and even injure humans. If you experience this type of severe weather you may also be at higher risk of being hit by a tornado. Read more in the tornado section for further details.

The Largest Hail in United States History
Hail size is influenced by intense updrafts, the layer of freezing altitude in the environment, and other advanced factors. The largest hail ever recorded in United States history measured 18.75 inches in circumference created by a strong updraft on June 22, 2003 in the small town of Aurora, Nebraska (largest circumference hail recorded to date). That record was reached again on July 23, 2010 near Vivian, South Dakota where hail was measured around 18.62 inches circumference (a record 8 inches in diameter, 1 inch larger diameter compared to the Aurora sample). Scientifically speaking, these stones may have been larger because the sample may have melted somewhat losing mass before the measurements were taken. In addition, the stones were of course broken in many cases due to contact with structures such as roofs, gutters, etc where chunks were broken off the main stone creating possibly smaller specimens than the original stone. What would the size be like? The answer is nearly the size of a vehicle hubcap. Imagine the damage that would occur. Even in doors, hail of this size can possibly penetrate some building materials.

Always stay away from windows and move to an interior reinforced room on the lowest floor of a sturdy well built structure. Large hail can also kill wildlife. Be sure to bring pets indoors as well.

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Lightning
Lightning is another danger from thunderstorms. As the atmosphere discharges electricity, leaders form powerful bolts. Although not considered to be severe alone, it is just as deadly. Bolts can be as hot as 50,000 degrees Fahrenheit. That's hot enough to fuse materials together, destroy structures, start fires, and definitely kill humans. Since lightning can move fractionally close to the speed of light (speed depending on the discharge and electrical properties of the atmosphere), there is no need to argue - one should not try to outrun strikes.

At any given moment there are nearly 2,000 thunderstorms occurring across the earth. Ice particles and atmospheric charges cause lightning to form leaders and channels resulting in lightning. Ever had your hair stand up in a lightning storm? Positively charged particles caused your hair to stand up as they rise from the ground indicating you are in danger and possibly becoming a target for a strike. Positively charged ice crystals ascend to the top of thunderstorms while negatively charged ice particles such as hailstones drop to the middle and lower altitudes in storms creating large differential electrical charges and thus vivid lightning.

In science gases expand when heated. If heated rapidly in a small fraction of time, explosive expansion occurs. This process can be described as an explosion or similar to a fire cracker sound, thus resulting in the thunder we hear.

On average, above 60 people are killed each year in the United States alone directly from lightning strikes. This number is likely lower than the actual impact on humans because not all strike incidents are reported. Lightning can occur up to 10 miles outside of the rain area or thunderstorm. It is also a good idea to seek shelter if you hear thunder, and wait to return outdoors until it is all clear and 20-30 minutes after the last sound of thunder you can hear. Your best bet for protection is to go indoors and stay away from windows. Lightning loves tall objects which are also made of conductive material. Telephone polls, towers, tall buildings, trees, and other objects are no place of safety during an electrical storm.

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Hurricanes
A hurricane is an organized tropical storm with winds at or over 74 miles per hour. Any hurricane can also contain other forms of severe weather such as tornadoes and of course flooding. The perfect conditions for a hurricane include warm moist water and relatively weak winds above them.

The National Hurricane Center predicts tropical storms. They are the agency which issues hurricane watches and warnings in the United States. On average, we experience at least five hurricanes per year.

Of the entire hurricane, the most dangerous weather often occurs near the eye wall of the storm. This relative clearing or "eye" of the storm is the center of counterclockwise rotation. High winds, tornadoes, and strong storm surges occur along the bands originating from the eye wall.

The size of a tropical storm system can be quite large - often several hundred miles in circumference. Thankfully energy is spread out over this distance as opposed to relatively smaller scale systems such as individual thunderstorm cells.


The Atlantic tropical storm season also known as hurricane season officially starts on June 1st and ends November 30th with activity peaking statistically in September. In the northeastern Pacific, the season starts May 15th and lasts until November 30th peaking in late August. Even though this is the officially recognized season, it is possible that tropical weather can occur nearly any time of the year, most often just outside of the official seasonal months.

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Tornadoes
Tornadoes are nature's most violent form of severe weather. Any severe thunderstorm can produce a tornado. The perfect conditions for a tornado include a supportive storm cell capable of producing a mature updraft or "Mesocyclone". Mature storms can become self supporting enabling them to live for long periods causing damage even across state lines. While it is possible for a tornado to occur without a classic Mesocyclone, the most dangerous often occur with it. There are many warning signs.

When conditions are favorable, your area made be included in a Tornado Watch. At this time you should pay close attention for any rapidly changing weather conditions. Just because it's clear outside doesn't mean you let your guard down. Awareness is vital here, as your life may depend on it. Large hail and high winds may also be a sign of impending tornadic activity. Rain free areas may also indicate your location is close to the updraft area of a severe thunderstorm. Pay close attention to media and your weather radio for any possible warnings.

If a tornado is indicated by radar or spotted by a person - a tornado warning is issued. At this time you should seek shelter in a sturdy structure away from windows on the lowest floor (find a central location in the structure). Cover your head with a mattress or pillow. Mobile homes are no place to be during a tornado. Abandon the mobile home unit if possible finding a ditch or nearby shelter (if time permits). If you are in a car, leave the vehicle, find a ditch, lie down, and cover your head. Be aware of possible flooding that may occur. Do not hesitate to take action.

There is no such thing as an "all clear" siren. It is also possible for more than one tornado to strike. Do not come out of shelter until cleared by officials, news media, or weather radio notification at the time the warning expires. Professionals will let you know when it's safe to come out or the threat has ended. Remember just because you can't see something yourself, doesn't mean it's not happening. Treat every warning the same - as if your life depended on it. Always have a plan of action for your family, business, or organization ahead of time.

Typically, although tornadoes can happen any time year-round, there is a peak period between the months of April and June. The common belief that tornadoes occur only during the afternoon is not true. Although daytime heating can meteorologically speaking assist in the dynamic environment for severe storms, tornadoes can also occur overnight. This makes it difficult to spot a tornado since Radar and lightning strike illumination, along with power flashes would be the only way to tell where a tornado was after dark. For this reason it is extremely important to have a NOAA Weather Radio.

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Damaging Winds
High winds can cause extensive property damage and injury. The National Weather Service considers winds severe when they reach or exceed 58 miles per hour. Damage can occur at this wind speed causing tree branches to break, windows to shatter, and weak structures to tear apart. Damage becomes more serious as wind speeds increase.

Straight line winds and down bursts can be just as damaging as tornadoes. The most common type of storm producing this kind of severe weather is called a "bow echo" because of its curvature (representing a bow). Dangerous winds can occur at the center of (and along) the bow echo. Remember other types of severe weather may also be occurring.


Live NOAA Weather Radio Online
The National Weather Service NOAA Weather Radio system operates in all states with radio transmitters broadcasting 24 hour weather information and warnings to the public. NOAA Weather Radio is capable of sending an alert tone designed to activate alarms in S.A.M.E. equipped models. After several requests have come into StormSector, we've found a link to online broadcasts of this system.

Online streams may not always work or be quality controlled. Some audio feeds may also be delayed. Don't rely on these streams as a warning source (only information). In addition, some links may not be operated by the National Weather Service (a third party). Click here for a list of online NOAA Weather Radio audio streams.

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