Severe Weather...Tornadoes

NWS Cleveland

Tornadoes: Development and Detection

Tornadoes are defined as violently rotating columns of air in contact with the ground. When they are not in contact with the ground, they are called funnel clouds. Tornadoes comes in different sizes, many as narrow rope-like swirls, others as wide funnels. Across the Plains, tornadoes can be seen from miles away. Across the eastern United States and the Deep South, tornadoes are often hidden in large swaths of rain and hail, making them very difficult to see, and thus even more dangerous.

A majority of tornadoes are labelled weak with wind speeds of 100 mph or less, and are usually on the ground for a few minutes. Even weak tornadoes can produce substantial damage. Some tornadoes intensify further and become strong or violent. Strong tornadoes produce winds up to around 200 mph. Most of the Ohio tornadoes that produce major damage are labelled strong. Only a few tornadoes across the country each year are labelled violent with winds of 200 to 300 mph. These tornadoes produce catastrophic damage, and can be on the ground for half an hour or longer.

The key atmospheric ingredients that lead to tornado potential are instability(warm moist air near the ground, cool dry air aloft) and wind shear (change in wind speed and direction with height). An unstable airmass promotes the development of strong updrafts. Wind shear not only increases the strength of the further, it also promotes storm rotation from which tornadoes are spawned.

All thunderstorms have the potential to produce tornadoes, but the type of storm that is most commonly tornadic is the Supercell. This very severe and long-lived thunderstorm contain a circulation aloft mesocyclone that grows upward through the storm and downward toward the ground. When conditions are just right tornadoes rapidly spin up from mosocyclones.

Dopplar radar can detect the circulation associated with a tornado-producing storm. Once the circulation is identified, a warning is issued. Dopplar radar is not perfect though. In fact, the radar only indicates rotation aloft, and does not indicate what may be occurring at ground level.

This makes the work of storm spotters very important. Only feedback from spotters can confirm whether the radar signature is associated with a tornado. The National Weather Service relies on the help of trained spotters. Working together, we can save lives.

Tornado Facts

FACT: Tornadoes travel at an average speed of 30 mph...but speeds up to 70 mph have occurred.

It is very dangerous to attempt to flee in your automobile, especially in populated areas. In addition, a car offers little protection against the strong tornadic winds. It is better to seek shelter in a sturdy building...but even a ditch or ravine offers more protection than an automobile. Move well away from your vehicle so that the strong winds do not roll the vehicle on top of you.

FACT: Tornadoes usually move from the southwest to the northeast...but have been observed to move toward the east or southeast on occasion...and can move very erratically at times.

The typical movement from southwest to northeast makes the southwest portion of a structure the the most susceptible to damage by a tornado's very strong winds. The safest portion of a sturdy structure is usually the northeast portion.

FACT:Opening windows may not protect your home from tornado damage.

It was once thought that opening windows prevented damage due to the sudden drop in atmospheric pressure as a tornado passed overhead. The atmospheric pressure within a tornado plays only a minor role at most in the damage process. Most structures have enough venting to allow for the sudden drop in pressure. Opening windows may lead to more damage inside structures...not less...due to very strong tornadic winds.

FACT:Tornado wind speeds increase with height within the tornado.

Storm cellars and basements offer the greatest protection from tornadoes.

FACT:Large hail may or may not precede a tornado.

Tornadoes often follow large hail. Often tornadoes develop within storms that do not produce hail. Large hail may also follow a tornado rather than precede it. Do not assume you are safe from tornadoes if you do not observe hail.

FACT:Tornadoes may occur at any time of the day or night.

It is important to have access to tornado warning information even when you are asleep. NOAA Weather Radio with a warning alarm device is the best tool to have to be notified when watches and warnings have been issued for your general area of the state.

When A Tornado Threatens...

Homes or Other Small Buildings

Go to the basement or an interior room or hall, or a small room such as a closet or bathroom on the lower level. Get under something sturdy like a heavy table or a bed.

Schools, Nursing Homes, Hospitals, Factories, and Shopping Malls.

Go to predesignated shelter areas. Interior hallways on the lowest floor are usually the best. Avoid large windows or glassed areas. Stay away from large rooms like a dining hall or gymnasium. Protect your head with your hands.

High-Rise Buildings:

Go to an interior room or hallway. Protect your head with your hands.

Mobile Homes, Automobiles(Including Buses):

Evacuate it and go to a substantial structure. If theres no shelter nearby, lie flat in the nearest ditch, ravine, gully, or other low spot and shield your head with your hands.

Remember...stay away from windows,doors,and outside walls, and protect your head. During the Tornado Drill planned for Wednesday February 26, 1997, determine what you would do if it were an actual emergency. Knowing what to do when a tornado approaches or a warning is issued and doing so quickly and calmly, will save your life!

For what to do on a Typical Severe Weather DayLook Here

For information on Wind and Hail

For information on Floods and Flash Floods

For information on Safety Tips

For information on Ohio Severe Weather