HTTP/1.1 404 Object Not Found Server: Microsoft-IIS/5.0 Date: Thu, 04 Jan 2007 17:02:03 GMT p3p: CP="CAO CUR ADM DEVa TAIi PSAa PSDa CONi OUR OTRi IND PHY ONL UNI COM NAV DEM" Content-Type: text/html Set-Cookie: v1us=ED5DC17E53725D9B; path=/; expires=Wed, 19 Feb 2020 14:28:00 GMT; domain=.usatoday.com

404 Object Not Found

 



 
 
 
HTTP/1.1 404 Object Not Found Server: Microsoft-IIS/5.0 Date: Thu, 04 Jan 2007 17:02:03 GMT p3p: CP="CAO CUR ADM DEVa TAIi PSAa PSDa CONi OUR OTRi IND PHY ONL UNI COM NAV DEM" Content-Type: text/html Set-Cookie: v1us=ED5DC17E53725D9B; path=/; expires=Wed, 19 Feb 2020 14:28:00 GMT; domain=.usatoday.com

404 Object Not Found

HTTP/1.1 404 Object Not Found Server: Microsoft-IIS/5.0 Date: Thu, 04 Jan 2007 17:02:03 GMT p3p: CP="CAO CUR ADM DEVa TAIi PSAa PSDa CONi OUR OTRi IND PHY ONL UNI COM NAV DEM" Content-Type: text/html Set-Cookie: v1us=ED5DC17E53725D9B; path=/; expires=Wed, 19 Feb 2020 14:28:00 GMT; domain=.usatoday.com

404 Object Not Found


HTTP/1.1 404 Object Not Found Server: Microsoft-IIS/5.0 Date: Thu, 04 Jan 2007 17:02:03 GMT p3p: CP="CAO CUR ADM DEVa TAIi PSAa PSDa CONi OUR OTRi IND PHY ONL UNI COM NAV DEM" Content-Type: text/html Set-Cookie: v1us=ED5DC17E53725D9B; path=/; expires=Wed, 19 Feb 2020 14:28:00 GMT; domain=.usatoday.com

404 Object Not Found


 

Tornado Chase 2000

May 4, 2000 - 7:00 p.m. ET

Where do tornadoes come from? Why do they continue to be so mysterious? The experts who chase down and study twisters up close for science answered your questions about tornadoes, storm chasing, severe weather and Doppler radar.

Meet the Tornado Team:

hbrooks.jpg (10038 bytes)
Harold Brooks  National Severe Storms Laboratory
vline.gif (10038 bytes)
dburgess.gif (10038 bytes)
Don Burgess  NEXRAD Operational Support Facility
vline.gif (10038 bytes)
demccarthy.jpg (10038 bytes)
Dennis McCarthy  Norman, Okla., National Weather Service
vline.gif (10038 bytes)
hbluestein.gif (10038 bytes)
Howard Bluestein 
The University of Oklahoma
cdoswell.jpg (10038 bytes)
Chuck Doswell  National Severe Storms Laboratory
vline.gif (10038 bytes)
dmccarthy.jpg (10038 bytes)
Dan McCarthy  Storm Prediction Center
vline.gif (10038 bytes)
jworman.gif (10038 bytes)
Josh Worman  University of Oklahoma School of Meteorology
vline.gif (10038 bytes)
dzaras.jpg (10038 bytes)
Daphne Zaras  NEXRAD Operational Support Facility
Read today's transcript below:


Comment from Chris Cappella, USATODAY.com: Welcome to today's second chat. We will get to as many questions as possible, starting with previously sent questions.


Chicago Illinois : Growing up downstate Illinois, i have seen my fair share of tornadoes,,,As the tornado storm approached my parents would say," As long as it's raining or lightning a tornado can't touch down". Any truth to this?

The Tornado Team: Basically, the short answer to this question is: No, there is no truth to this. Tornadoes can occur that are entirely wrapped in heavy rain, and I have seen lighting near tornadoes on many occasions, and even some film/video footage where lightning flashes have occurred WITHIN the tornado's funnel-shaped cloud.

Chuck Doswell
National Severe Storms Laboratory


Bedford, Texas : I live in a second floor apartment, and I cannot seem to find advice on what to do if a tornado is heading my way. All of the safety tips I read this year are for people that live in houses. I'm not going to knock on my downstairs neighbor's door every time there is a warning and hide in her bathtub, because there seems to be one every other night this time of year. My plan now is to run out in the street and try to drive away. That sounds silly, I know, but I really don't know what to do. A lot of my friends live in apartments too, and they have the same concerns. Is there simply no good advice, or are we basically ignored by the experts because we don't own property, or are we just sitting ducks? What should apartment dwellers do, and why are we ignored by the experts? Thanks for your time, Tom Blackwell Bedford, TX

The Tornado Team: If you feel bad about knocking on your downstair neighbor's door, the next best thing is an interior hallway if there is one available! There is still your interior bathroom that is an option. The option of getting in your car should be a last resort because you could end up in traffic gridlock, i.e. like the Jarrell, TX situation on I-35. If you know of a shelter nearby, or better yet, to get your apartment complex to have a designated shelter working with your local Emergency Management would be a wonderful way to prepare well in advance!

Dan McCarthy
Storm Prediction Center


Lexington, KY : The tremendous wind speed doppler measured (318 mph) in the 5/3/99 Oklahoma City tornado was only 1 mph short of a "mythical" F6 rating. Based on this, have tornado experts reconsidered the theoretical upper limit of a tornado's wind speed? As I understand it, experts previously thought that an F6 was theoretically impossible. Thank you. Rick Schrantz

The Tornado Team: First of all, there are some technical questions about whether or not the "Doppler on Wheels" measurement truly was 318 mph. As the data are reviewed, this number might well be reduced.

Second, the measurement was taken about 175 feet above the ground, whereas the Fujita scale refers to damage at the surface (where the buildings are). Any relationship between measurements that far above the surface and damage at the ground is not known precisely, but we DO know that the strongest windspeeds in a tornado ARE somewhere above the surface.

Third, the windspeed numbers established by Professor Fujita have never been "calibrated" ... that is, we don't really know what windspeeds are associated with a specific level of damage. In fact, the relationship between windspeed and damage is very complex, so it's unlikely that the windspeed values associated with the Fujita scale should be taken literally. They are only "ballpark" numbers.

In effect, F5 damage is "total destruction" when it comes to the effects on a well-built frame home. It is not at all clear how we would RECOGNIZE F6 damage, if it ever occurred. It's not that an F6 is "theoretically" impossible ... it's that the Fujita scale is a damage scale based on what happens to a well-built frame home. What could be BEYOND "total destruction"?

Chuck Doswell
National Severe Storms Laboratory


Houston, Texas : What is the strongest tornado ever record?

The Tornado Team: Our records focus on the damage caused by tornadoes, not their intensity, since we don't have a good way to measure the intensity. On average, about 1 F5 (the highest rating on the damage scale) occurs each year in the United States. We can't really tell the difference between them. The deadliest US tornado on record is the 18 March 1925 so-called "Tri-State" tornado that went across southeastern Missouri, southern Illinois, and southern Indiana, killing 695 people.

Harold Brooks
National Severe Storms Laboratory


LARKSPUR, COLORADO: It appears that Tornado's travel East, Northeast most of the time, why is that?

The Tornado Team: In general, the motion of a tornado doesn't differ too much from the motion of the thunderstorm that produces it. Thunderstorm motions, in turn, are influenced mostly by the winds within the surrounding atmosphere.

Again speaking in general terms, tornadic thunderstorms in the United States form in conditions where the basic windflow is toward the East or Northeast. Therefore, most tornadoes move in the way you've described. However, not ALL tornadoes behave this way, so no one should ASSUME that a specific tornado is going to move toward the east or northeast.

Chuck Doswell
National Severe Storms Laboratory


watertown, wisconsin : On the movie twister, tornadoes are talked about on an F " " scale. What was the biggest tornado in the world and how much damage did it do? Is there such a thing as an F7 or F8 tornado?

The Tornado Team: The F-scale is a scale for rating the amount of damage done by a tornado. It is called the "F-scale" because it is named for its inventor, the late Professor T. Theodore Fujita, from the University of Chicago. This scale is also associated with windspeed estimates, but the windspeeds should not be taken literally. The damage is based on the effects of the tornado on a "well-built" frame home.

Since we do not know very much about tornadoes around the world ... tornadoes DO occur worldwide ... and we know very little about tornadoes that happened more than about 40-50 years ago, it is impossible to say what was the "biggest tornado in the world" or the "strongest" or "the fastest" or whatever.

Although the details are not known very clearly, it appears that the most damaging tornado in U.S. history may have been a tornado that hit downtown St. Louis, Missouri, in 1896. It was a violent tornado that stayed within populated areas throughout all of its path ... in today's dollars, it may have done more than 2 billion dollar's worth of damage.

There is no reason to believe that tornadoes ever become more intense than F5 on the Fujita scale.

Chuck Doswell
National Severe Storms Laboratory


Columbus Ohio : I am caught on the freeway with a tornado bearing down on me. Farmers fields on both sides of the road. There are drainage ditches on both sides with an approximate depth of 2 - 3 feet. Do I stay in the car or leave the car and get in the drainage ditch?

The Tornado Team: This is a very good question and one I tried to cover at the recent Ohio Severe Weather Symposium at Ohio State. Think of your options: 1) stay in the car; 2) take cover in an overpass; 3) take cover in the ditch. Which would you choose?

The best option to me would be the ditch. One problem is the case of heavy rain which accompanies many Ohio tornadoes. But, my chances are better in the ditch than in a car or overpass. The car can become airborne Also, debris can pierce the car like a knife through butter. This was seen in the Oklahoma City tornado and the Xenia tornado in 1974. My best advise is know where you are relative to the tornado. If possible, get off the highway and try to take cover in a building trying to get walls between you and the tornado. Consider the option of the ditch, placing blankets and such over your head for protection from flying debris. Get down below 3 feet. It was found out that more debris exists above three feet than anywhere relative to the tornado.

Dan McCarthy
Storm Prediction Center


Honolulu Hawaii: Why isn't there more imphasis put of prepardness . Most states offer incentives to install solar heating on houses , why not offer the same incentives to building storm cellars . I grew up in Arkansas and spent many a night in a storm cellar .

The Tornado Team: Actually, there is strong emphasis in the Plains states and Ohio Valley in building storm cellars or safe rooms. The Federal Emergency Management Association (FEMA) promotes the use of safe rooms. I don't know if any of the insurance agency will offer discounts for having safe rooms. Many of the new construction that is going up in Oklahoma and Texas now includes safe rooms.

Dan McCarthy
Storm Prediction Center


Frank, Cedar Rapids, Iowa : What are the best websites to keep track of active storms? What is the forecast for this season for tornadic activity in Iowa?

The Tornado Team: One of the best web sites I have used for tracking storms is www.weathertap.com. This is a site where you can get up to the minute radar data in a very timely manner. They also have forecasts available for aviation and have satellite images available. You can monitor NWS products using weather.gov (no www in the front) to monitor warnings and watches. If you want more web locations, go to one of the many search engines out there and search for weathernet it ahould take you the University of Michigan's popular site listing hundreds of weather links.

Dan McCarthy
Storm Prediction Center


Eureka, KS GW 100 : The National Weather Service's Attitude Toward Cold Air Funnels, Seems To Be They Don't Do Any Damage. I Live In A Trailer House. I Don't Care If It's A Cold Air Funnel Or An F-0 Tornado, I'll Probably End Up With The Same Damage. I Realize Cold Air Funnels Don't Show Up On Radar, But The Danger Should Not Be Downplayed.

The Tornado Team: Actually, cold air funnels and F0 tornadoes are very different things occurring in very different situations. The definition of a tornado is "a violently rotating column of air in contact with the ground." Some occur without funnel clouds. Cold air funnels sometimes occur under cool low pressure systems when the ground is well heated and cumulus clouds form. The rotation from the low pressure system provides a good environment for the updrafts in the cumulus cloud to rotate. This can produce a cold air funnel cloud. Since they are not really produced by thunderstorms, with all of the inflow, rear-flank downdraft etc. which are part of that process, they rarely, if ever make contact with the ground. The National Weather Service forecast office will often issue statements or forecast updates about cold air funnels, but they rarely issue tornado warnings for them since they are not "violently rotating columns of air in contact with the ground." At this point, when we see strong enough rotation in a thunderstorms, especially if that is supported by spotter reports, we will issue a tornado warning, but we don't usually know in advance how strong the tornado will be. We are very concerned about any storms which could produce tornadoes.

Dennis McCarthy
Norman, Okla., National Weather Service


Ihlen MN: How can you use the Doppler effect to warn a town if a tornado is coming?

The Tornado Team: Doppler radar is probably the biggest advance so far in tornado warnings. The WSR-88D (NEXRAD) system has been deployed around the U.S. at National Weather Service forecast offices. The radar can distinguish objects moving toward it from objects moving away from it. When we see high-speed inbound objects adjacent to high-speed outbound objects, relative to the radar, we can infer a rotation. If the rotation is cyclonic (counter-clockwise) and strong enough, we have evidence that the thunderstorm and its rotating updraft are strong enough to produce a tornado. This gives us the chance to issue a tornado warning with enough lead time for the residents of a city to take shelter. The system is still not perfect, but it has improved very much with the deployment of Doppler radars.

Dennis McCarthy
Norman, Okla., National Weather Service


waterford,wi: what was the largest tornadoe recorded (width)in the state of wi, and how long was it on the ground?

The Tornado Team: The widest tornado on record in Wisconsin was on 18 May 1898 in Marathon County. It was 1500 yards wide, was on the ground for 30 miles, killed 12 people, and is rated F5.

The longest-track Wisconsin tornado was on 5 April 1929 in Pierce, St. Croix, Dunn, and Barron Counties. It was 75 miles long, 400 yards wide, killed 7 people, and is rated F4.

I think the general scientific consensus is that tornadoes don't care about whether the location is downtown or not. Downtowns aren't hit very often because they aren't very big. The chances of a downtown that's 2 x 2 miles big, for instance, are the same as the chances of the other 2 x 2 mile areas nearby.

Harold Brooks
National Severe Storms Laboratory


Chicago,IL : When trapped inside a home or office building during a tornado, where is the safest place in (1) home. Is is fact or fiction that opening windows in the home reduces atmospheric pressure so the house will not explode? (2) In an office building, on an upper floor, should we hide under our desks?

The Tornado Team: The safest place in the home is in the basement underneath a stairway or within an interior room...something sturdy! If you do not have basement, an interior bathroom or hallway is preferred.

In an office, an interior stairway is best and try to get to the lowest floor as possible. Get down and protect your head from flying debris.

Dan McCarthy
Storm Prediction Center


San Jose, CA : Would it be possible to stay in the center of a tornado as it moves and survive until it dissipates?

The Tornado Team: It seems like, theoretically, that it would be possible to travel along in the middle of a tornado and survive, but I cannot imagine it would happen in real life. There is an "eye" in tornadoes, similar to the one in hurricanes, but it is so small and there is so much debris traveling at extremely high speeds that it would be hard to survive the experience without being killed or seriously injured. The biggest danger in a tornado is from high speed debris. This why we suggest that people go to a basement, a shelter, or an interior room on the lowest floor of a building. We also know that trying to take shelter under a highway overpass is very unsafe since you are still exposed to the high speed debris. You can learn more about tornado safety on National Weather Service and NOAA Web sites.

Dennis McCarthy
Norman, Okla., National Weather Service


chicago illinois : what kind of weather are we expecting for this summer, as far as tornados

The Tornado Team: We don't have any ways of making seasonal forecasts of tornadoes. All we can do is look at the typical numbers that have occurred in the past. For that, you can look at the NSSL Hazards Project for national information.

Harold Brooks
National Severe Storms Laboratory


Cincinnati, Ohio : I've always wanted to be a storm chaser. Is it possible for a person who isn't one to go on a chase with a group of stormchasers?

The Tornado Team: Yes, it is possible to do this. There are two quite different ways to hook up with an experienced storm chaser. One way is to look for a "chase tour" business ... there are several that can be found by doing a Web search. These are businesses that provide you with a storm chase "tour" as part of a group of customers.

The other way is to contact an experienced chaser directly. There are some chasers who are looking for partners to share expenses. However, most veteran chasers do not need partners, so it may be difficult to find someone willing to let you come along.

There is a Storm Chase Homepage on the Web where you can "advertise" your interest in finding a chase partner and it also includes links to some of the "Chase Tour" businesses.

If you are interested in chasing, be prepared for lots of frustration, disappointment, and expenses. Real chasing is not like that in the movies!

Chuck Doswell
National Severe Storms Laboratory


Fort Worth, TX: Recently, a tornado devestated some high rise office buildings here. Cash America building is roughly 14 stories high. Where is the best place to take shelter in a building such as this? I would think ground floor, in the middle to be safer.

The Tornado Team: Your thinking is correct. The lowest floor possible is the best location towards the middle of the floor. Hopefully, the building's stairwells are not located near the outer walls, but in the middle of the building so that you could take them to the lowest floor. Don't forget to make yourself as low as possible when you get to that floor and cover your head to protect yourself from flying debris.

Dan McCarthy
Storm Prediction Center


Atlanta, GA : IS the basement the only "safe" place in a house when a tornado strikes? Can you give suggestions for other places that are safe?

The Tornado Team: The basement is probably the safest place, if you have one and if you also have a place in the basement to get under something sturdy, something like a workbench or stairs. There are other safe places however. You can build or install a safe room or shelter. Many companies now offer this service, and you can find out more about them on the Federal Emergency Management Agency's web site: www.fema.gov or at Texas Tech University's web site. You can also reinforce a first-floor bathroom or closet, even though they offer pretty good shelter anyway. In my home, our shelter is a downstairs bathroom at the middle of the house, underneat the stairs going to the second floor. This works pretty well for most tornadoes. The violent F5 tornadoes like the one which struck Oklahoma City last year are very rare. In these cases, a basement or below-ground shelter would be best, but a well-constructed first-floor safe room would work pretty well.

Dennis McCarthy
Norman, Okla., National Weather Service


York, PA: Does the USA have more tornadoes than any other country? Who comes in second, third?

The Tornado Team: The United States has more tornadoes than any other country, but it's hard to tell how to rank the other countries, since only Canada and the US have official report collection agencies. In other countries, the reports are collected by amateurs working on their own time. Tornadoes have been observed on every continent except Antarctica. Other than North America, the country that gets the most strong and violent tornadoes is probably Bangladesh, although they've been observed in Argentina, South Africa, and northwestern Europe in the last 40 years.

Harold Brooks
National Severe Storms Laboratory


Eau Claire Wisconsin : Question for Don: Why in the last 6-8 months I have seen these perfect round cirlces on radar. They are as small as a state and sometimes as large as a region? Mike

The Tornado Team: The circles to which you refer (large circles of high reflectivity) are a part of the calibration of the radar. They are produced by test signals that are generated to test to processing and display done by the radars. The signals are injected into the system by the technicians as they do their normal maintenance or specially-needed maintenance on the radar. The technicians are supposed to make sure that the connections that transmit the radar images to users are stopped when they perform maintenance, but sometimes they forget. When the forget, you see the circles. Small circles of weak reflectivity are normal residual ground clutter and are seen often, particularly during the night when more of the radar energy is bent back toward the ground.

Don Burgess
NEXRAD Operational Support Facility


Dallas, TX : Why does hail seem to always accompany tornados?

The Tornado Team: Of course, the weather changes all the time! If there is anything that we can say about the weather is that it constantly changes. It also is true that we may be seeing evidence of climate change. However, the fact that a thunderstorm near you moved from east to west is not necessarily all that indicative of something happening to change the climate.

In my 28 years of storm chasing, every year, I see something I've never seen before. The weather has many possibilities, and most people will only see a tiny fraction of all those possibilities within their lifetimes.

Chuck Doswell
National Severe Storms Laboratory


dallas Texas : I seem to see a change in weather. The other day a thunder storm came across my place from east to west never in 47 years have I seen that. could a tornado come from a storm like that?

The Tornado Team: Of course, the weather changes all the time! If there is anything that we can say about the weather is that it constantly changes. It also is true that we may be seeing evidence of climate change. However, the fact that a thunderstorm near you moved from east to west is not necessarily all that indicative of something happening to change the climate.

In my 28 years of storm chasing, every year, I see something I've never seen before. The weather has many possibilities, and most people will only see a tiny fraction of all those possibilities within their lifetimes.

Chuck Doswell
National Severe Storms Laboratory


Houston Texas : What are some of the damages that are inflicted by a tornado that would cause you to catagorize it as an F5

The Tornado Team: An F5 tornado is one that causes "increincredibleage. Some things that are used as examples of incrediablincrediblee: well-built houses completely blown away with nothing left on the house site (usually a bare concrete slab; reinforced concrete structures (public buildings and others) very heavily damaged on completely destroyed; or large missles/prmissileses carried large distances (examples are telphone ptelephoners and trucks, oil/water storage tanks, etc). Another thing that is seen sometimes is the ground completely scoured of grass and up to an inch of top soil removed, or strong/tall trees, reduced to stumps or short trunks that have had the bark removed. If there are no strongly-built structures, missiles, or strong trees in the path of the tornado, the documentation of the F5 category may not be possible. Many times there is not much difference between strong F4 and F5, and some people tend to clump F4 and F5 into one category of violent tornado.

Don Burgess
NEXRAD Operational Support Facility


itasca il : Even with the weather channel there seems to be a delay in getting the information out because the weather channel goes to a commercial break either before or after issuing a warning. The local stations send out the crawl on TV but there seems to be a 7 to 10 min delay between the actual time of the warning and when you see it on tv. How can this be reduced. This is more important at night because the tornadoes can't be seen as well unless they run into power lines or lighting happens to flash nearby to make them more visible.

The Tornado Team: There are many steps in the warning decision making and dissemination process. They happen much faster these days but we are still working on speeding them up even more. A warning is issued by a National Weather Service forecaster by drawing an area over his/her radar display. The workstation makes a text product with coding built in for automated display systems. The warning travels by telephone lines to these systems. They include the "red screen" and crawl on The Weather Channel, crawls and county maps on local TV stations, etc. Most of the time it takes less than one minute for this to happen, but there can be computer "hangs" or other system delays. One of the fastest ways to hear a warning is over NOAA Weather Radio which is now automated in most areas also. You might also purchase a scanner and learn the frequencies used by local spotter networks. You should see warning dissemination continue to get faster in the months and years to come. It is something we are working very hard to improve.

Dennis McCarthy
Norman, Okla., National Weather Service


Des Moines, IA : What is the average speed of travel of a tornado?

The Tornado Team: Tornadoes can travel at speeds as slow as just a few miles per hour or as fast as 50 to 60 miles per hour, but the average is around 25 to 30 mph, especially for the more significant ones. They travel at the speed of the parent thunderstorm. The violent tornado which struck Oklahoma City this time last year moved at about 28 mph. Most move from southwest to northeast, but since they move with their parent thunderstorm, it's important to listen and watch for information on how the storms are moving during an event.

Dennis McCarthy
Norman, Okla., National Weather Service


Yukon Oklahoma : It seems like more and more tornadoes are hitting in and near large metropolitan areas. And it seems like we're seeing more and larger tornadoes each year. Is this a coincidence, or is there an explanation for these phenomen?

The Tornado Team: Our records/statistics show that the number of violent tornadoes has stayed about the same since about 1950 (when good tornado record keeping began). The number of weaker tornadoes, however, has increased quite a lot. We think the increase in the numbers of weaker tornadoes comes from better reporting and better sensors (like Doppler radar) to detect tornadoes. As far as more strong tornadoes hitting metropolitan areas, the statistics do not bear that out. Instead, I think we are just getting more publicity through the media and more TV coverage of the events. With about 1,200 tornadoes in the U.S. every year and about 25% of them being strong to violent, there is pretty large probability of at least one or two metropolitan areas being struck every year.

Don Burgess
NEXRAD Operational Support Facility


WARWICK RI : why not send a "black box" type of video recorder into the center of a tornado..... I realize that this would take a few attempts. Recover and replay the info???

The Tornado Team: The idea of getting data from inside a tornado has been around for quite a while ... the first attempts began more than 20 years ago. In fact, this idea forms a big part of the movie "Twister". We HAVE been trying to do this, but with only limited success. It is not easy to put a data collection device into a tornado and, so far, we haven't had much luck. There have been some near-misses and some limited data from a handful of tornadoes.

Part of the problem is that even if we HAD a complete success someday, learning a lot during the passage of a single tornado doesn't do us a whole lot of good. We would really need to sample MANY tornadoes and do it MANY times during their individual lifetimes before we truly could do much of scientific value with the data. Of course, ANY data would be better than NO data!

Most meteorologists believe that remote sensing observation systems, like mobile Doppler radars, are our best hope for getting the sort of comprehensive data we need to advance our understanding of tornadoes.

Chuck Doswell
National Severe Storms Laboratory


Comment from Chris Cappella, USATODAY.com: Thanks for all of the excellent question. We have about 30 minutes left, so keep them coming.


St. Charles, Missouri: I recently moved here from So. California and am suprised at how nonchalant people are when the sirens go off. We had a warning a couple of weeks ago, and it was real close by the way, and people were still out driving around as if it was no big deal. I took shelter in my basement and prayed. Shouldn't I take the sirens seriously?

The Tornado Team: YES! The sirens should be taken seriously. I guess sometimes it takes someone to knock on the door to tell one a tornado is coming. The exact same thing happened on April 26, 1991 as a tornado moved into Andover, KS. Video from a police car showed people in a mobile home park out walking their dog as the sky to the west was very dark and sirens were blaring away! Fourteen people were killed in that mobile home park, because they did not take the warning and move to shelter.

Dan McCarthy
Storm Prediction Center


Grand Island, Nebraska : Has there been any recent research or gains in using Infrasonics to detect tornadoes?

The Tornado Team: Our sister lab in Boulder, CO is actively researching this subject, the Environmental Technology Lab. I'm sorry I don't know the current work.

However, the older work in the 1970s seemed unclear as to whether Infrasonics would ever be useful. The only incident of a well documented tornado nearby to an Infrasonic network showed that the network did not detect a signal until the tornado *dissipated*.

For more information on current work, though, please visit our sister lab, the Environmental Technology Lab. There should be a link to them from http://www.oar.noaa.gov/

Daphne Zaras
National Severe Storms Laboratory


Pittsburgh, PA: I grew up in central Oklahoma (with fond memories of weathermen Gary English ("...stay with 9, we'll keep you advised..." and Fred Norman). I remember hearing as a kid, instructions from an anonynmous voice-over on the TV during a Tornado warning that you should "open the windows in your home and them move away from them" and seek shelter. I think the idea at the time was that the barometric pressure around the tornado is so low that houses would literally "explode," even if not in the direct path of the tornado, due to the differences in pressure outdoors vs. indoors. Has this theory and this advice been discredited now, or is it correct?

The Tornado Team: This idea has indeed been discredited! We now know that the pressure forces on the home are simply due to the winds blowing around the building. In fact, the forces are inward on the windward side of the house and outward on the sides and far side (leeward) of the home. FEMA has a very nice animation of this on their web site. I don't recall the exact URL, but it is most likely under the Mitigation Program, possibly on the BPAT (Building Performance Assessment Team) page.

The windows will most likely break due to the debris blowing around in the winds.

The National Weather Service sometimes includes the following line in their warning messages "don't open the windows... the tornado will do that for you." :-)

Daphne Zaras
National Severe Storms Laboratory


Annapolis, Md: In the Mid-Atlantic region, what are the key variables to look for that can turn thunderstorms, which are common here, into extremely dangerous weather, such as a tornado?

The Tornado Team: The factors are really the same wherever these storms occur. We look for an unstable atmosphere. The most unstable conditions would be warm moist air at the lower levels of the atmosphere and cold air in the upper levels.

When we have these conditions occur we can get severe thunderstorms. If these conditions are combined with a wind profile that goes from south or southeast at the lowest levels to westerly at the upper levels of the storm...and increasing with height...then it can develop storm scale rotation and become a supercell storm. Supercell storms produce the large majority of strong and violent tornadoes.

These condtions come together less frequently in the east than the Midwest or Plains...thus a lower frequency of tornadoes.

Jim Purpura
National Weather Service Forecast Office, Norman, Okla.


Overland Park, Kansas: What is the likelyhood of seeing a tornado in a heavily populated area?

The Tornado Team: Tornadoes are not likely to be in heavily populated areas simply because they do not occupy much square footage in our country! Open up a state map to see what I mean--the cities are very small compared to a lot of rural land.

However, there is nothing special about a city when a tornado is concerned. It will go where the parent thunderstorm goes!

Daphne Zaras
National Severe Storms Laboratory


Kentwood, MI: What is the difference between a tornado and a waterspout?

The Tornado Team: By weather service definition a waterspout is a tornado over water. However, by common definition among researchers waterspouts are commonly seen under rapidly growing cumulus towers over a body of water. They are characterized as having very smooth laminar walls. Tornadoes, on the other hand, are more complex. They often form on the interface between air descending in rear of a storm and the updraft. They often are preceded by a larger, storm scale rotation. Tornadoes most often have ragged walls, multiple vortexes and come in a variety of shapes. Some are cylindrical, some are rope shaped, some are shaped like an elephant trunk and some are just large wedges in contact with the ground. Several from the May 3, 1999 tornado outbreak fit this latter category producing damage over mile in diameter. Some researchers believe they have documented smooth laminar flow in tornadoes that they call landspouts.

Dave Zittel
NEXRAD Operational Support Facility


HERSCHER, IL. 60941: How does one become a weather spotter? I watch the weather channel faithfully and am very intuned with the storms and I would like to be involved as a volunteer to serve in this capacity for the local networks.

The Tornado Team: To become a spotter talk to your city or county Emergency Manager. The NWS office in your area can usually tell you whom to contact.

Requirements differ by Emergency Manager. You will need at the minimum to attend NWS spotter training, In some of our areas, like Wichita Falls, they need to be Ham Radio operators.

Jim Purpura
National Weather Service Forecast Office, Norman, Okla.


Fort worth, TX: Why do tornadoes seem to stay on the plains and infrequently hit major metropolitan areas. Does it have anything to do with heat(hot air), pressure, or lack of oxygen.

The Tornado Team: It's more a factor of geography than anything else. There simply is more open country, areally speaking, than urban areas in much of the US outside of the Eastern Corridor. Tornadoes DO hit populated areas, as shown in Fort Worth last month, and Nashville last year.

There may be some effects on storms due to urbanization that we don't understand as of yet. But the reason is mostly geographical.

Jim Purpura
National Weather Service Forecast Office, Norman, Okla.


Saginaw, Michigan: What has been longest time that a tornado has been on the ground?

The Tornado Team: The longest track known occurred in the Tri-State tornado, March 25, 1925. This tornado traveled from southeast Missouri just south of Cape Girardeau through southern Illinois into southwest Illinois. It was on the ground for almost 4 hours. The tornado demolished the town of Murpheesboro, IL. The tornado killed over 600 people.

Dan McCarthy
Storm Prediction Center


Hampton Virginia : How much of a role does helicity play in the occurrance of tornadoes?

The Tornado Team: Helicity is a measure of the lowest 3 km (9000 ft.)of how the winds change with height. It is measured in energy units m squared per sec squared. We plot these winds on what we call a hodograph and connect the end points on to the next to create a curve. We then take the direction and speed the storm will move and place that point on the graph. Lines are drawn from that point to the first point and the one at 3 km. The helicity is the area between those two lines and gives us an idea of the potential to produce rotating storms in the low and middle levels of the atmosphere. One must be careful in using these numbers as a northeast wind at the surface and a westerly wind at mid levels would create huge numbers. But, the northeast wind would not bring in warm and moist air that the storm needs to be fed. It would bring in cooler air. The storms needs warm and moist air from the southeast or south to enhance storm growth. Add then the turning of the winds with height and that they increase in speed with height would add to the storms rotation and enhance tornado potential.

Dan_McCarthy
Storm Prediction Center


Carlsbad California: Is there any evidenve that the heat and air disturbance that is produced by jet aircraft flying across the country and around the world is causing tornadoes. rcooke@pacbell.net

The Tornado Team: We have no evidence that jet and aviation is linked to the increase of tornadoes.

Actually we may not have more tornadoes than in the past. We may just be seeing more of them.

With the appearance of storm spotters, storm chasers and doppler radar...many tornadoes that might have gone undetected are now reported.

As evidence of this...we used to tell people that about 2/3 of tornadoes are weak (F0 and F1), a bit less than a third are strong (F2 and F3), and 1 or 2% are violent (F4 and F5). Now it's more like 88% weak, 11% strong...and 1% violent. The increase in weak tornadoes is most likely due to more spotters and chasers seeing more weak tornadoes that would have been unreported in the past.

Jim Purpura
National Weather Service Forecast Office, Norman, Okla.


Mascoutah, IL : Do tornadoes increase in power over water?

The Tornado Team: Hmm.... good question. I don't think anyone knows for certain, and if we did investigate we would have difficulty knowing that the change was due to the surface change! Tornadoes constantly change their strength, size, etc. during their lifetime.

A few studies looked at changing the surface conditions under a physical model tornado. The inflow jets increased in strength when the surface was rougher. Someone else looked at this in a numerical tornado model and I believe they had similar results. However, the caveat here is that a model tornado is not a real one. Physical models in particular are very different in key ways from real tornadoes which may prevent these studies from being applicable to real life.

Daphne Zaras
National Severe Storms Laboratory


Alamogordo, NM: A tornado hit my hometown in Illinois in the '60s. I feel safe living in New Mexico, but can you tell me if there has ever been a report of a tornado in New Mexico? One was reported in nearby El Paso, Texas last spring.

The Tornado Team: There are a fair number of New Mexico...most of them are in the plains east of the Rockies.

No place in New Mexico is entirely safe from tornadoes. You probably don't need a below ground shelter as much as you do in the plains or midwest...but you should at least identify an interior hallway or closet as your safe place...and share that information with your family.

Remember that damaging winds from severe thunderstorms are no stranger to New Mexico...and are much more common than tornadoes.

Jim Purpura
National Weather Service Forecast Office, Norman, Okla.


Norman, OK: How does the rotation inside the mesocyclone become so concentrated?....what makes it intensify?

The Tornado Team: One of the scientists at the National Severe Storm Labratory, Dr. Lou Wicker, has studied mesocyclone circulations using model data. His conclusions were that as low level flow relative to the storm increased the mesocyclone became more concentrated as horizonal streamwise vorticity tilted into the updraft and interacted with the descending rear flank downdraft. Thus, this interaction increased the rotation inside the mesoscyclone and enhancing tornadogenesis.

Dan McCarthy
Storm Prediction Center


Boulder, Co: In your opinion, what have been the 3 largest technology advancments in the last 100 years that have saved peoples lives?(from tornadoes)

The Tornado Team: I think the 3 most significant technological advances has been radar, computers, and either satellites or storm models. Even before NEXRAD, the National Weather Service radars defined the location and strength of thunderstorms, and were useful in determining storm strength. NEXRAD added Doppler technology that allowed forecasters to observe the circulations within thunderstorms that generate tornadoes. The weather service skill in detecting and warning for tornadoes and severe weather has increased significantly with the use of NEXRAD.

The NEXRAD system and other advances in storm warning capability would have been impossible without the ability to process large amounts of data by computer. As computers get faster and cheaper, even more gains should be realized.

Storm models have provided significant information on the processes that produce severe weather and tornadoes, and have led to major increases in storm warning accuracy and lead time. These models have been particularly effective in defining the atmospheric conditions that allow or cause tornadoes to generate.

Satellites provide continous monitoring of the nation's weather and techniques have been developed to use satellite data and images to improve both our ability to monitor severe weather.

Tim O'Bannon
NEXRAD Operational Support Facility


Comment from Chris Cappella, USATODAY.com: Thanks to everyone for participating today at both the 1:00 and 7:00 ET chat sessions. We have just about 10 more minutes.


Baltimore, MD: I live near Baltimore Maryland, what are the chances of a tornado hitting somewhere in this area? Thanks!

The Tornado Team: Hi, glad you asked! I recently helped our Dr. Harold Brooks put his Severe Thunderstorm Climatology work into some web pages which are designed for the general public to understand (I hope we succeeded!).

Note that the data is all relative to within 25 miles of a point.

Go to: http://www.nssl.noaa.gov/hazard/ and click on "Total Threat." Then click on the .gif file for 1980-1994 All Tornadoes (http://www.nssl.noaa.gov/hazard/img/ttor8094.gif). Baltimore is in the darker blue color, which shows as .6 to .8 on the scale. Those are "tornado days", or day on which at least one tornado occurred within 25 miles of a point. 0.6 to 0.8 mean that it'll happen less than once per year in Baltimore. At least, according to what has been reported in the past! By the way, we restrict the data to 1980-1994 because the tornado and other severe weather reports are best during this time period.

There are many other ways to view the data. A favorite of mine is the "Annual Cycles." Click on that page and then click on "tornado" and then click on or near to Baltimore. You'll get a graph showing your annual cycle for the year. The probability of seeing a tornado on any given day of the year is shown in percent.

I.e. your highest chance of a tornado through the year is around July 15 and the chance on that day was 0.75 % based on data from 1990-1994 (the black line is the 15 year average). In January and February the chance is basically zero! For fun, click on a point in the southeast Gulf coast states (i.e. southwest Georgia) and notice that their chance is NEVER zero. They have a minimal chance of a tornado all year. Now click on southwest Oklahoma. We have a very definitive tornado cycle. I would actually rather live here than in soutwest Georgia because of this: I basically know when my tornado threat is! (Though I do keep in mind that my threat isn't quite zero except in January).

Be sure to look through those pages. There is some great information in the Severe Thunderstorm Climatology!

Daphne Zaras
National Severe Storms Laboratory


Cedar Rapids, Iowa: Do you anticpate more tornados in the midwest this year, and if so why? Any connection to la nina?

The Tornado Team: It is really difficult to make seasonal forecasts for tornadoes in any part of the U.S. Normally, tornadoes frequent that of Texas northward through Nebraska every year, and Iowa gets it's share. So far, there have been 240 tornadoes this year through May 4 which is way behind that in each of the last three years.

There has been no solid connection to La Nina and tornado occurrences across the U.S. Last year's La Nina connection coincidentally brought tornadoes to Arkansas in January, yet below average occurrences February through April. This year it has not been that way at all. The jet stream patterns across the western U.S. are linked to increase precipitation in the intermountain regions relative to La Nina. But, these jet stream patterns retreat northward in the spring and make La Nina unrelated to tornadoes in the midwest.

We have seen one relationship, El Nino does result in an increade southern jet stream across the Gulf of Mexico and hence tornadoes in Florida and parts of the southeastern U.S. Beyond that, there is no relationship.

Dan McCarthy
Storm Prediction Center


Lubbock TX: Why do so-called LP (Low Precipitation Supercells) have a lower frequency of tornadoes than other Supercell thunderstorms?

The Tornado Team: As with many of these questions...we don't know for sure...but believe it is related to the weak downdrafts that are present with these storms (as compared to classic or high precipitation supercells).

The Rear Flank Downdraft (RFD) is believed to be related to the formation of a tornado. It needs to be just the right strength. If it's too strong the storm will be outflow dominated and "gust itself out". If it's too weak (as with LP Supercells) the tornado may not form under these conditions either.

Jim Purpura
National Weather Service Forecast Office, Norman, Okla.


Comment from Chris Cappella, USATODAY.com: Thanks to everyone for participating today at both the 1:00 and 7:00 ET chat sessions. And thanks to our panel of tornado experts from the National Oceanic and Atmospheric Administration. That is all time we have. Good night.