Tornadoes
Experts Say
Tornado expert Gary Conte joined a Weather Watch bulletin board from September 5-24, 2003.
Student: Is your work hard?
Gary Conte: Forecasting the development and track of mostly weak tornadoes across the New York City Metro Area is quite difficult, even when trained skywarn spotters supplement radar observations.
Student: Hi. I am in an Earth and Space Science class and we are supposed to do a project. I am doing a project on F4 and F5 tornadoes. Can you give me any interesting information on those two types you know?? Thanks.
Gary Conte: F4 and F5 tornadoes are classified as violent tornadoes. Less than 1% of all tornadoes that occur are violent, resulting in 70% of all tornado deaths. The lifetime can exceed 1 hour and wind speeds are greater than 205 miles per hour.
Student: What do you do when a tornado strikes?
Gary Conte: I would take cover in a house or building. I would go to the lowest floor and proceed to a central location, away from windows. If your house has a basement, go to it. If not, the best place is usually an interior bathroom or closet on the first floor.
Student: How do tornadoes start?
Gary Conte: Before a thunderstorm forms, a change in wind direction and a rapid increase in wind speed with increasing height above the earth's surface create an invisible horizontal spinning effect in the lower atmosphere. Rising air within a thunderstorm updraft tilts the rotating air from horizontal to vertical. An area of rotation, 2–6 miles wide, now extends through much of the storm. Most tornadoes form within this area of strong rotation.
Student: How do they stop?
Gary Conte: When tornadoes move into an atmospheric environment that is unfavorable, they dissipate by lifting back up to the sky.
Student: How far can they go?
Gary Conte: Weak tornadoes may touch down briefly for less than one tenth of a mile. Violent tornadoes can travel for 25 to 50 miles.
Student: I have heard the myth that tornadoes will jump a house and then destroy one. I was iffy on believing this one. So can you finally clear up my doubtfulness on this issue? Thank you.
Gary Conte: It is quite possible for a weak tornado to briefly touch down, lasting less than 30 seconds, before lifting back up into the cloud. Yes, it is possible.
Student: Where is the worst place for you in a tornado?
Gary Conte: If you are out in an open field or an open area, this would be the most harmful location, without any personal protection.
Student: How can I get out of the middle of a tornado?
Gary Conte: You have to wait until the tornado moves past your location.
Student: How can you measure tornados?
Gary Conte: Doppler weather radars are used to estimate wind speeds above the ground. Surface observing systems are used to measure wind speeds on the earth's surface.
Student: I will be moving to Whitehall, PA. Does this area get hit with tornadoes???
Gary Conte: Although tornadoes occur most frequently in Oklahoma, they can occur anywhere, including Whitehall, PA. However, the frequency of tornadoes is much less in Pennsylvania than in Oklahoma.
Student: How can you tell if a tornado is coming?
Gary Conte: Your National Weather Service Office will issue a Tornado Warning based on Doppler Weather Radar and volunteer skywarn spotter reports BEFORE a tornado occurs. These warnings will be seen on television and heard on radio. If you look up at the sky and notice a green color, see a circular cloud rotating and can hear a loud roar similar to a freight train, a tornado is coming!
Student: Will you die if you’re in the center of a tornado??
Gary Conte: You might. It depends on the intensity of the tornado and where you are as the tornado approaches your location.
Student: When and where did the highest number of tornadoes occur? What was the largest area destroyed by a tornado?
Gary Conte: Violent tornadoes, which are classified as F4 and F5 tornadoes, most frequently occur from Texas north to Nebraska, which is known as Tornado Alley.
Concerning your question about historical tornadoes, please check the Storm Prediction Center's Frequently Asked Questions About Tornados for answers.
Student: Where do tornados come from?
Gary Conte: Tornadoes develop from well-defined severe thunderstorms that have large and intense rotating updrafts. This 2 to 6 mile wide area of rotation is called a mesocyclone.
Student: What technology do you use to predict tornadoes? And how is it used?
Gary Conte: Weather satellites, radar, wind profilers, and surface observing systems are all used to monitor the environment for the development of severe thunderstorms that can produce tornadoes.
Doppler weather radar and trained volunteer skywarn "spotters" are used to "warn" for tornadoes. Radar "looks" above the ground. Spotters "look" from the ground and supplement radar data.
Doppler weather radars are the primary tools used to forecast the development of tornadoes. Because it can "sense" movement of air toward or away from the radar, it can be used to detect areas of developing rotation within the atmosphere that precedes tornado development.
Student: How can I keep from being scared of tornadoes?
Gary Conte: There is educational literature that you can read that focuses on safety at school, at home, and other places.
Some sites that have information on tornado safety include the National Weather Service, the American Red Cross, and Sky Diary's Kidstorm. Learn about tornadoes, how they form, how you can be notified of a tornado warning, and what actions you can take to protect yourself.
Learn about tornadoes, how they form, how you can be notified of a tornado warning, and what actions you can take to protect yourself.
Some sites that have information on tornado safety include the National Weather Service, the American Red Cross, and Sky Diary's Kidstorm.
Student: Hi, I was wondering are all tornadoes dangerous? And also how do you find out where tornado a tornado is going to be? Well that’s all my questions for now. I have to read lots more on tornadoes! Bye!!
Gary Conte: All tornadoes are dangerous, but some are more dangerous than others. About 88 percent of all tornadoes that occur are weak, rated as F0 and F1 with wind speeds up to 112 miles per hour. They cause moderate damage. Less than 1 percent of all tornadoes that occur are violent, rated F4 and F5 with wind speeds over 200 miles per hour. They cause incredible damage.
The National Weather Service's (NWS) Storm Prediction Center issues Tornado Watches across the entire United States. Your local NWS office issues Tornado Warnings for your local area.
Your local National Weather Service Office will issue Tornado Warnings, telling you the direction and speed the tornado is moving. The warning will list the communities in the path of the tornado and the approximate times it will impact the communities.
Student: When do tornadoes really start coming in the year?
Gary Conte: Although tornadoes can occur at any time of year throughout the United States, they are most frequent east of the Rocky Mountains during the spring and summer. They typically occur during the afternoon and evening from 3 to 9 pm.
Climatologically, the highest frequency of tornadoes occur during the afternoon and evening from March through May in the Southern U.S., May through July in the Central U.S., and June through August across the Northern U.S.
Student: Have there been any tornadoes this year (2002)?
Gary Conte: Yes, tornadoes occur throughout the United States every year. About 941 tornadoes occurred during 2002. For the latest tornado occurrences, check the National Weather Service's U.S. Tornado Summaries.
Student: When does the tornado season begin?
Ingrid Amberger: Tornadoes can occur at any time of the year. In the southern states, peak tornado occurrence is in March through May. While peak months in the northern states are during the summer.
Note, in some states, a secondary tornado maximum occurs in the fall.
Tornadoes are most likely to occur between 3 and 9 p.m. but have been known to occur at all hours of the day or night.
Gary Conte: Across the Southern U.S., it begins in March; across the Central U.S., in April; and across the Northern U.S., in May. However, tornadoes can and do occur any time of the year.
Student: Who has the most tornadoes, Wisconsin or Alabama? What about the worst ones?
Gary Conte: Hi. From 1950 through 1998, 18 tornadoes were reported in Wisconsin and 21 were reported in Alabama.
...AND the WINNER is...Alabama.
Student: How do tornadoes form? What states can get the worst tornadoes and most damage? How do F5 tornadoes start?
Gary Conte: The 3 key ingredients to produce a thunderstorm are: low and mid-level moisture in the atmosphere, atmospheric instability, and a source of "lift" (such as a cold front, warm front, dry line, sea breeze front, etc.).
For tornadoes to develop within thunderstorms, you need a rapid turning of the wind direction AND a significant increase in wind speed with increasing height above the ground. This creates an invisible horizontal column of air in the lower atmosphere. Rising air currents (updrafts) within the thunderstorm tilts the rotating air column from horizontal to vertical. An area of rotation, 2-6 miles wide, now extends through much of the storm. Most strong and violent tornadoes form within this area of strong rotation.
Because of the unique geography of the U.S., most severe thunderstorm producing tornadoes occur in "tornado alley" covering the states from Texas north across Nebraska. This includes the states of Oklahoma and Kansas.
Student: Can tornadoes happen anywhere? If so, how you don't hear about tornadoes in the mountains or in big cities like New York or San Francisco?
Gary Conte: Yes, if the "right" weather ingredients come together, tornadoes can and do form anywhere.
Here are a few examples:
The last tornado to strike the NYC Metro Area occurred during July 7, 1976. An F1 tornado with estimated wind speeds up to 112 mph passed within 1/4 mile of the statue of liberty. Significant damage occurred in nearby urban areas. During the past few years, several tornadoes have struck U.S. cities such as Salt Lake City in Utah and Dallas in Texas.
As far as mountains go, in the late 1980's, a tornado swept through Yellowstone National Park leaving a path of destruction both UP and DOWN a 10,000-foot mountain.
Student: We live near Lake Michigan. Are we less likely to have a tornado by the lake?
Gary Conte: NO. Please read this Tornado Myth and Fact.
MYTH: Areas near rivers, lakes, and mountains are safe from tornadoes.
FACT: No place is safe from tornadoes. In the late 1980's, a tornado swept through Yellowstone National Park leaving a path of destruction up and down a 10,000 ft. mountain.
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