Previously Asked Questions

Thunderstorms and Severe Weather

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Nick,
Where did the saying "the calm before the storm" come from?
Fran
Mashpee, Massachusetts, on Cape Cod  

Fran, 
This common phrase has become part of our everyday language and is used to describe many experiences other than weather.  But it probably had its beginnings among weather observers.  The idea that there are calm weather conditions just before a storm has been around a long time.  The quotation “calm continueth not long without a storm” reportedly goes back to 1576. 

Just before a line of thunderstorms moves into an area, many of us have noticed the wind cease and an eerie calm set in that forebodes the storms to come.   The Weather Channel’s Severe Weather Expert Dr. Greg Forbes explains that this might happen when a warm front brings cloudy, drizzly and cool conditions with light winds that suddenly give way to strong thunderstorms with gusty winds, heavy rain and hail as the front passes.  Also, large-scale storms such as Nor’easters can seem to suddenly bring on wind and rain, replacing the calm conditions that high air pressure may have brought just hours before. 

When it comes to hurricanes and other tropical cyclones, air inside the intense low pressure center rises and then often descends outside the storm.   In those cases, sinking air (high pressure) makes for clear skies and relatively light winds on the periphery of the storm, creating a “calm” atmosphere just before the fury of the cyclone moves in.   But this does not happen in every case. 

Sometimes the “calm before the storm” may be in our minds.   Because storms often seem to move in suddenly, creating such a drastic difference from the conditions we experienced just before the storm, the “pre-storm” weather often seems calm by comparison.  So we may simply perceive that there was “calm” before the storm.  Other times weather conditions change gradually, with rain and wind increasing ahead of a storm system, so there is no calm, just a progressive intensification. 

Can tornadoes happen anytime or only in certain times of the year?
Wendi 

Why do tornados happen most in tornado alley?
Sherise Henson 

Wendi and Sherise, 

Tornadoes can form in any month in the United States, but the largest average number of them in the past ten years has come in May, followed closely by June and April.  They have occurred in every state of the U.S. and on every continent of the world except Antarctica where the air doesn’t have enough moisture for thunderstorms to form. But as you mentioned, most occur in the central part of the nation. “Tornado Alley” includes portions of Texas, Oklahoma, Kansas and Nebraska.  They get more tornadoes here than anywhere else in the country (and anywhere else in the world, for that matter) because these states are in the perfect spot to get warm moist air from the Gulf of Mexico, cold air from Canada and dry air from the west.  When that combination comes together, as it does quite often in this area, the air can become unstable, and that makes conditions ripe for a tornado to form. During the period between 1989 and 1998 those four states (TX, OK,  KS, NE) averaged thirty percent of all tornadoes annually.

How far away can you hear a tornado?
Kristal
Nevada, MO

Kristal,

I put this question to The Weather Channel’s severe weather expert Dr. Greg Forbes.  He tells me that that the distance varies with intensity of the tornado and atmospheric conditions, but most people can hear a tornado from a mile away, and sometimes from several miles away.

Is it true that we should not take a shower during a thunderstorm?
Danielle
Sleepy Hollow, IL

Lightning kills more people on average every year than tornadoes and hurricanes combined.  The simplest way to avoid danger is to get inside a home or other sturdy building during a thunderstorm   But even indoors, you should watch what you do. Lightning injuries are rare indoors, but even so, it is best not to talk on a corded telephone, don't take a bath or shower, and don't use electrical appliances.  If lightning strikes outside phone lines, electrical wires or pipes, the electrical current can travel indoors.  Also, never watch lightning from an open door or window.  It's almost as dangerous as staying outside. 

With some pre-planning and by following some simple rules, you can avoid the danger of nature's light show, and enjoy its beauty instead. 

For more on thunderstorm safety from the National Weather Service, go to their agency’s lightning safety pages at  www.lightningsafety.noaa.gov/

What time of year are tornadoes common in Florida?
Garrett Kirkland
Indian River Charter High
Vero Beach, FL

Garret,
With all the thunderstorms in the summer months from heating and ample moisture, Florida has plenty of opportunities for tornadoes any month of the year.  The sea breezes and other wind shift lines along rivers and lakes can be the source of the rotation for these tornadoes. But June is the peak time, with an average of just under 350 tornadoes during the month.  May is next, with a little more than 250, followed by July with a little less.   November averages the least number of tornadoes, with about 90 or so.  For a graph of tornadoes month-by-month in Florida, you can go here: http://www.srh.noaa.gov/mlb/images/gif/fltormth.gif 

Because the jet stream dips farther south into Florida during March and April, tornado deaths actually peak at this time of the year, though the deadliest tornado outbreak was in February of 1998.

Dear Nick,

During periods of heavy lightning I have always felt safe, or maybe that should be safer, when I'm in a car. When I'm at home and lightning occurs, I always avoid talking on the phone. My question: What’s the best advice for those times when riding in a car in a lightning storm and your cell phone rings?
Wayne
Atlanta 

Dear Wayne,
Just to make sure on this, I checked with The Weather Channel's severe weather expert Dr. Greg Forbes.  Here is his reply: 

“There is no increased danger of answering your cell phone in the car, unless you have it plugged into your car's cigarette lighter socket as a power source. Being in a car isn't an absolute guarantee of safety, as there was a recent example of a car's interior being damaged by lightning, but that's a very rare event. Being in a car is generally safe because of the metal at top and bottom of the car.  The highly conducting metal gathers all the electric field to it, leaving the interior free.  The electric field is like an attracting force for an approaching lighting current. Talking on a telephone that has a cord attached is dangerous because the current may come through the wiring and into the headset.  Being in contact with appliances is dangerous, too, because some of the lightning current may come through the wiring.  Being in contact with plumbing - the toilet, bathtub, faucets, etc. - is dangerous because some of the lightning current may come through the pipes.”  

So Wayne, you are doing exactly the right thing when it comes to your home phone. And as long as you use a battery-operated cell phone, you should be fine.  Just be sure to pull over to the side of the road to answer it, as thunderstorms can bring heavy rain that makes it tough enough to drive in without trying to talk on the phone at the same time!

What is ball lightning?
Lauren
Tavares, FL

Ball lightning is a mysterious and rare phenomenon that has been known to occur with strong thunderstorms.  People have reported seeing glowing balls of light about the size of bowling balls floating through the air or passing through the glass in windows.  One report even had a ball of lightning rolling down the aisle of a jetliner.  Another report speaks of a blue, white and orange ball entering a factory in England and bouncing around the machinery in showers of sparks before vanishing. Because it is so rare and lasts only two or three seconds before it disappears, ball lightning is hard to photograph. 

Ball lightning seems to occur with other lightning strikes, but there seems to be no agreement among scientists of how it forms, and some scientists wonder if it even exists at all, other than as an optical illusion.

Dear Nick,
I’m an educator at the Museum of Science, Boston.  After a recent program on weather, a young visitor asked me why the sky appears to turn green during a tornado.  I’ve heard that this happens, but didn’t know the answer and promised to try to find out.  Can you help?  
Many thanks,
Richard Hedderman
Programs Division Museum of Science, Boston

Richard,

The sky does sometimes turn green when severe thunderstorms are present, but there may or may not be a tornado forming.  The green color is not completely understood, but one theory states that clouds will turn a greenish color if 1) The clouds contain a very high amount of liquid water drops and perhaps hail, and 2) the thunderstorm forms early or late in the day near times of sunrise or more typically sunset. 

Here’s how it works.  Liquid water (as well as ice) is actually slightly blue in color (meaning that it absorbs red light weakly.)  However, this color is so weak that it requires a thickness of tens of feet before it becomes apparent (much larger than the dimensions of a glass of water, for example).  However, scuba divers can vouch for this, as objects seen beneath the surface of the water by more than ten or twenty feet do indeed appear bluish. 

As you know, the sky turns a shade of orange or red at sunset.  But why?  It’s because the distance that sunlight travels through the atmosphere is much longer when the sun is low in the sky.  Because atmospheric particles (dust, salt, smoke, pollution) scatter blue light more than red, the longer path of the sunlight through the atmosphere leaves sunlight depleted of blue and therefore rich in orange and red. 

The combination of reddish light from a horizon-hugging sun and the slightly blue color of clouds filled with water can result in greenish light. 

Since many severe thunderstorms do form late in the day, and many tornado-producing thunderstorms also contain abundant liquid water, the green sky is often associated with tornadoes, but again, it is not the tornado that causes it.

Nick,
What is a land spout?
John T. Nichols Jr. Middle School
Middleboro Massachusetts  

Whereas stronger tornadoes come from severe thunderstorms, a “landspout” is the name that is sometimes given to a small, relatively weak tornado that comes from towering cumulus clouds that usually do not produce lightning or thunder. A landspout can form without any warning signs from Doppler radar or observations, but winds in the spinning vortex can be strong enough to cause minor damage.  The name “landspout” comes from the term “waterspout” which is a similar type of twister that forms over water.

 I know hurricanes always spin in the same direction in the Northern Hemisphere. How about tornadoes, do they vary?
Kathy
Grand Rapids, MI

Kathy,

About 99.9% of all tornadoes spin cyclonically, which in the Northern Hemisphere is counterclockwise, and clockwise in the Southern Hemisphere. (That’s the direction of spin looking down on the tornado, not up into it) As you mentioned, this is the way hurricanes spin, as well as larger midlatitude weather systems that produce rain and snow storms. The reason for the counterclockwise spin is Earth’s rotation.  As air moves from areas of high air pressure to areas of low air pressure, Earth’s rotation sets up something known as the Coriolis force, named after French scientist Gustave-Gaspard Coriolis, who wrote about it in 1835.  The Coriolis force causes wind to curve around to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.  Generally, this cyclonic direction of spin translates down to individual thunderstorms and the tornadoes spawned by them.  

But when it comes to tornadoes, there are a few documented exceptions to the rule.  The Weather Channel’s Severe Weather Expert Dr. Greg Forbes says an average of one tornado every year spins in the opposite direction.  These are formed by very localized wind shear effects inside a thunderstorm.  The strongest usually occur right beside a nearby strong cyclonically-spinning tornado.  Amazingly, the tracks of these two opposite-spinning tornadoes run parallel to one another.

Nick,
Is it possible for a tornado to occur while it is snowing?
Ashley
Lee's Summit, MO

Ashley,
I talked to The Weather Channel's severe weather expert about this and here is what he told me:
"I don’t remember any tornadoes in snow. I have heard of a rare tornado with surface temperatures in the 30s, but don’t know if it was snowing. More likely there was a cold rain, with unstable warm conditions above. However, it would be possible to have a snow devil (a spinning whirlwind caused by thunderstorms in the mountains), and it’s not out of the question that a lake-effect snow squall could spin up a brief whirlwind as well."

He also pointed out that last Thanksgiving Day, there was a tornado reported in Phippsburg, Maine on a fairly cold day. Although there was no snow, in nearby Portland Maine the high temperature that day was only 43F. There was a strong surface low, cold front, and upper trough going across the area.  The tornado was classified as an F1, with maximum winds estimated at 100 mph.  It damaged several buildings along its two mile path.  By the way, this was the latest tornado on record in Maine, with records dating back to 1950.

How come some tornados miss a house and hit the others around it?
Kristal
Nevada, MO

The diameter and path of a tornado can be very small in comparison to the thunderstorm that produced the tornado.  Some tornadoes can be only a few feet in diameter, but within that small area, the winds can be well over one hundred miles an hour.  That’s strong enough to severely damage or even destroy a home.  As a tornado moves through an area, only those buildings directly in its path will experience those damaging winds.  The more narrow the tornado, the more narrow its path, so it’s easy to see why a tornado might destroy one home while another next door or across the street may escape undamaged.

I heard that recent thunderstorms caused a lot of damage from straight line winds. What are straight line winds?David
White Sulphur Springs, WV

The term “straight line winds” refers to any thunderstorm winds you might find at the surface which are not from rotation in the storm.  With gusts to 100 mph or more, they can often cause as much damage as a tornado.  In fact, it may take a survey of the damage to tell whether it was the result of a tornado or from straight line winds. A tornado tends to scatter debris in many directions, but straight line winds blow only in one direction.  They’re usually caused by strong downdrafts, or air rushing down out of the thunderstorm to the ground.

How does hail form?
Mrs. Gustafson's science class
Bloomington, MN USA  

Dear Mrs. Gustafson’s class,

Hail forms in strong thunderstorms.  These storms contain very strong updrafts, which are winds blowing up through the thunderstorm clouds.  They can be as strong as one hundred miles per hour.  Those strong updrafts suspend rain in mid-air with temperatures around the raindrop of below 32 degrees.  Those cold temperatures allow the rain to freeze into small hailstones.  As more freezing raindrops get caught in the updraft, they collide with the hailstones, adding layer after layer of ice.  When hail becomes too heavy for the updrafts to keep it aloft, it falls to the ground.    In strong updrafts, the hail has time to collect lots of ice, so the hail is bigger.  In weak updrafts, the hail doesn’t have to get as big before it is able to fall to the ground.  On rare occasions, the updrafts can be strong enough so the hailstones can grow larger than softballs! 

Nick  

How do tornadoes grow to be a bigger size? Why does the fujita scale only go up to an F5?
Christa
St.  Johns, Maryland 

Christa,

Just to make sure we’re on the same page, remember that the size of the tornado (how wide it is) is no indication of how strong it is.  Tornadoes that cover a small area can be stronger and more violent than those that cover a wide area. The Fujita scale is actually a measure based on the damage caused by a tornado, rated from minimal damage at F0 to total devastation at F5. It is all about the damage. The winds are estimated from the damage, not the other way around.

The Fujita scale is named for the late Dr. T. Theodore Fujita, a University of Chicago researcher, who created the damage scale based on his studies of tornado aftermath scenes over three decades. Originally from Japan, Fujita studied the damage in the aftermath of the 1945 atomic bombs at Hiroshima and Nagasaki before coming to the U.S. and turning his attention to tornadoes. Every known U.S. tornado since from 1950 to 2007 is rated according to his scale, based on a post-storm analysis conducted by National Weather Service meteorologists who study the scenes of storms. (There is a new enhanced Fujita scale now, called the EF scale.  Find information about it here: http://www.spc.noaa.gov/efscale/

Meteorologists observe the kind of damage, the degree of damage and the orientation of wind-strewn debris to first determine if a tornado did in fact take place, and then to rate the tornado according to the Fujita Scale.

Also, many storms predating the Fujita scale have been rated by Thomas Grazulis in his historical reference "Significant Tornadoes," largely based on estimates made from whatever records or accounts of damage are available.

The Fujita scale has many weaknesses, many of which were noted by a team of meteorologists and wind engineers that studied the scale for the Storm Prediction Center. Most notably, it is highly subjective, often fails to recognize differences in construction between damaged homes, and is hard to apply in situations where a tornado doesn't hit a structure -- an extremely intense tornado crossing an open field could get a low rating if it doesn't happen to hit a building.

The team devised an enhanced Fujita scale that will go into effect Feb. 1, 2007. The new scale will use 28 different damage indicators to more precisely determine tornado intensity, including some non-structure damage indicators such as hardwood and softwood trees, and also will feature a finer differentiation in varying structure designs. This is a recognition that it takes less wind than earlier thought to cause more damage. Past violent tornadoes will not be re-rated according to the new scale, but will merely be presumed to have had somewhat weaker winds than earlier believed.

Why do we have tornadoes?  How are they made?
Mrs. Ratliff's Kindergarten class
Barrera Veterans Elementary
Von Ormy, Texas

Dear Ms. Ratliff’s class,

The central United States is the perfect spot to get different kinds of air masses coming together.  For example, warm moist enters from the Gulf of Mexico, cold air comes from Canada, and dry air flows in from the west.  With that combination, the air can become unstable, and that makes conditions ripe for tornados. They form in strong thunderstorms when wind speed or direction changes from the lower part of the storm cloud to the upper part.  Rising air, called an “updraft” helps form the rotation within a thunderstorm. The updraft can stretch the spinning air tighter, causing it to reach incredible speeds above 200 miles an hour. Thunderstorms also have sinking air, called “downdrafts,” which help the rotation reach below the cloud to the ground.  Often the spinning air is invisible until it picks up dust from the ground.   

The United States has more tornadoes than anywhere else on earth, with an average one thousand occurring every year.  If you hear a tornado warning, act quickly and get to a closet or hallway on the lowest floor of your home, away from outside walls and windows until the danger passes.  It is best for your family to have an emergency plan before storms hit, so talk with your parents about what to do if you hear a tornado warning for your area.

Nick

Hi,
When we hear about the number of tornado reports in one day, how do we know whether or not some of those reports aren’t of the same tornado?
Gary
Madison,WI.
 

Gary,
The National Weather Service puts out a preliminary report of how many tornado reports it receives in a day, and our own Severe Weather Expert Dr. Greg Forbes also keeps track of tornado reports and lets viewers of The Weather Channel know the total number.  It is true that often these reports are from two or more people looking at the same tornado.  So later, meteorologists go back and try to determine how many, if any, of those reports were of the same tornado.  Sometimes they have to actually go out and survey the damage paths of tornadoes to determine how long each lasted and the areas each covered. Then the meteorologists can come up with a revised and more accurate count of how many tornadoes there were in a particular day.  Surveying the damage from a tornado is also how meteorologists determine its wind speed, and thus it’s strength on the Fujita (now Enhanced Fujita) scale.

Nick,
How fast does marble and golf ball size hail fall from the sky?
Michael

Michael,
It varies. The speed at which objects fall to the ground depends on their weight and how much air resistance they encounter. So the heavier the hailstone, the faster it would fall, and the rounder the hailstone, the faster it would fall, since it would encounter less wind resistance than a flatter hailstone. Falling raindrops and thunderstorm updrafts (winds blowing up in a thunderstorm) or winds blowing horizontally might also slow the hailstone's fall, but thunderstorm downdrafts (winds blowing down) could speed up its fall. It has been calculated that the terminal velocity of a golf ball sized hailstone is 70 to 80 miles an hour and about 45 miles an hour for marble-sized hail. Terminal velocity is the greatest speed at which an object will fall in calm air based on its weight and air resistance. But because air in a thunderstorm is never calm, hailstones may never reach their terminal velocity.

How can it lightning and snow at the same time?
K.C.
Boston, MA

It doesn’t happen too often, but now and then we see thunderstorms that produce snow.  We call it, as you might guess, “thundersnow.”  For thunderstorms to develop, we need an unstable atmosphere.  This usually happens when there’s plenty of warm moist air near Earth’s surface, and much colder air above.  That’s common in the spring and summer, but usually if it’s cold enough to snow, it’s also too cold at the surface to get much instability for thunderstorms.   

But it can happen. Some winter storm systems with very cold air in the higher atmosphere can pull in enough warm moist air from the Gulf of Mexico to provide the instability for thunderstorms.  And when very cold air passes over a large unfrozen body of water such as the Great Lakes, the relatively warmer water in the lake can help create the necessary instability for thundersnow.  Several years ago I saw several flashes of lightning as snow was falling in Seattle.  Just as thunderstorms can produce heavy downpours of rain, thundersnow storms are known for producing several inches of snow in a short time.

I heard on The Weather Channel that lightning is a major killer, so why do people say that you have a one in a million chance of getting struck by it?
Victoria
Brooklyn, NY

Victoria,
Actually, your chances of being struck by lightning are much greater than one in a million. In fact, the National Weather Service calculates a one-in-three hundred chance that you or a family member will be struck by lightning sometime during your lifetime.  And because people don’t realize how common lightning injuries are, it ends up killing more people on average every year than tornadoes and hurricanes combined.  

You can beat the odds fairly easily, though. The simplest way is to get inside a home or other sturdy building during a thunderstorm.  Do it immediately; don't wait for the rain to fall.   Most lightning injuries occur before the rain starts and after it stops.   Remember, if you hear thunder, lightning is close enough to strike you.  If you are caught outside during a thunderstorm with no buildings nearby, you should avoid open fields, beaches, lakes and swimming pools. Lightning often strikes the tallest object around, and you don't want that object to be you.  That's also why isolated trees, picnic shelters and covered bus stops offer no protection, and may actually increase your chances of being struck.  If no other shelter is nearby, get into a car with metal sides and roof, and roll the windows up. The National Weather Service has more on lightning statistics and safety precautions here: http://www.lightningsafety.noaa.gov/ 

Nick

Nick,
Is it true that if there is thunder, there has to be lightning, or when there is lightning there has to be thunder?  And looking at the forecast, why would there be more of a chance of storms on a sunny day then a cloudy day?
Katie
Valencia, CA

Katie,
Yes, thunder is a result of lightning.  When lightning strikes, it heats the air quickly enough to cause air molecules to scatter apart at "lightning" speed. This causes the explosion of sound we call thunder. So if there's no lightning, there's no thunder. And there will always be thunder as a result of the lightning, though you may be too far away to hear it.

Strange as it may seem, sunshine can actually increase the chances of afternoon and evening thunderstorms on warm humid days. The sunshine causes the air to rise, taking with it the abundant moisture in the air. This builds tall thunderstorm clouds that can cause quick downpours. Afterwards, skies may clear again.

Dear Nick,
Recently I was at my farm just after it had quit raining. It was between 60 and 65 degrees when suddenly I was hit with a blast of hot air probably 85 or 90 degrees. I spun around to see if there was a fire behind me, but there was nothing. I had never heard of that and neither had anyone else I mentioned it to. People gave me funny looks, and I've decided not to mention it to anyone else. What actually happened?

Stan
Springfield, MO

Stan,

It sounds as if you may have encountered a heat burst, a fairly rare phenomenon that happens below a decaying high-based thunderstorm if all the right factors come together.  If the air below the weakening storm is dry enough, rain or snow or melting hail begins to evaporate in the dry air, which makes the air cooler and denser than the air around it.  As a result, the air accelerates downward.  Since the sinking air comes from very high in the atmosphere, it builds up a lot of momentum.  Once all the precipitation in the air evaporates, the air stops cooling.  However, because it has so much momentum already, the air continues to sink and begins to heat up due to compression, the same way air inside a bicycle pump warms as it is compressed.  Warm air usually has a tendency to rise though, so its descent will quickly slow down.  If it doesn’t reach the ground first, the air will actually start to rise again.  That’s the key to why a heat burst is so rare: the precipitation has to evaporate out at just the right time so the warm downdraft reaches the ground before its momentum is gone.  If it does, a quick 10 to 20 degree jump in temperature is possible.  Also common is rapid wilting of vegetation in the area due to the blast of hot dry air. 

I’m sorry you got funny looks from people, but as you can see, there is a reason behind what you encountered.  Plenty of other people have shared your experience; in fact, there is a description of one such event in South Dakota from the National Weather Service page at http://www.crh.noaa.gov/fsd/soo/heat/heat_burst.htm 

Now you can start telling your story again!

What is the record for the most tornadoes in 24 hours?
Mrs. Schmitt’s Classroom
Wallenpaupack North Intermediate School
Lake Wallenpaupack, PA  

Dear Mrs. Schmitts's class,
Thousands of people will remember April 3-4, 1974 when 147 tornadoes were spotted over a period of 16 hours.  It is commonly (and rightly) called the "Super Outbreak." In all, thirteen states were struck by twisters: Alabama, Georgia, Illinois, Indiana, Kentucky, Michigan, Mississippi, North Carolina, Ohio, South Carolina, Tennessee, Virginia, and West Virginia.  330 people died, and 5,484 more were injured in a damage path covering more than 2,500 miles.

Nick,
What is the percentage of thunderstorms that occur in the United States in the fall?
Zach  

Zach,

I posed your question to The Weather Channel's Severe Weather Expert Dr. Greg Forbes.  Here is his answer:  

“It is difficult to count individual thunderstorms. We detect thunderstorms in basically two ways. In one, an observer at a weather station hears thunder or sees lightning. Data from this source is traditionally kept in the form of ‘thunderstorm days,’ the number of days per month and year that thunder is heard at a station. The observer has difficulty knowing exactly how many individual thunderstorms are causing the thunder/lightning.

A second way that we detect thunderstorms is with some lightning detection system. Using such a system, data are kept on lightning strikes, but those strikes are not easily grouped into an exact number of thunderstorms.

What I have done is grouped thunderstorm day data from about 240 stations across the United States for the fall months (September, October, and November) and for the year. Using this data, 16% of the annual thunderstorm days occur during those 3 fall months. This is probably a pretty good measure of the percentage of thunderstorms that occur during the fall, although the percentage may vary a bit from location to location.”

Thank you for your help, Greg.  And thank you, Zach, for your question.  Interesting stuff!
Nick Walker

Nick,
Which event kills more people world wide annually--Floods, Earthquakes, or Lightning?
Chestnut St. Nazarene School
Hawthorn, PA

We don’t have accurate statistics on worldwide fatalities from natural hazards.  However The Weather Channel's severe weather expert Dr. Greg Forbes gathered statistics on the 100 deadliest disasters of the 20^th century.  From those events, floods and tropical storms killed 8.1 million people, while slightly more than 1.5 million died in earthquakes.  Because smaller events are not counted, we don’t have accurate annual averages.   If we use just those top events, floods killed an average of about 81,000 people per year and earthquakes killed at least 15,000 people per year during the last century.   

Dr. Forbes points out that in any particular year, the number of fatalities can switch from one cause to another, depending upon whether floods or earthquakes are more serious.  For example, in the thirty years from 1970 to 1999, it’s virtually a tie between flooding/tropical storms and earthquakes worldwide, when almost half a million people died from each cause.  But if you had excluded the year 1970 when 300,000 people died in flooding in Bangladesh, then earthquakes, by far, would have been the leading cause of death from natural disasters.  

Our lightning fatality statistics are not accurate even in the United States, and almost nonexistent on a global basis.  In the U.S. lightning kills about 100 people per year on average.   If you convert this to a death rate per million people and then apply that rate to the world population of about 6.1 billion people, then an average of about 2,440 people are killed around the world by lightning every year.   This seems logical, since many of the countries with the largest populations are also those that get a lot of thunderstorms.  This would make lightning come in a distant third in the rate of fatalities. 

If we speak only of the United States, flooding is the leading killer of the three.  From 1972 to 2001, an average of 127 people died from floods, while lightning experts estimate 93 deaths from lightning.  During that period, tornadoes claimed an average of 65 lives per year, hurricanes killed 16 people, and six people died in earthquakes.  

The sad thing about flooding deaths is that almost of them are preventable. More than half occur when people drive their vehicles into flooded roadways and are swept away by moving water.

If you are tempted to drive over a flooded road, here are some things to remember:
1.     Two feet of water can float a car away.  Six inches can sweep you off your feet.

2.     It is very difficult to get out of a floating car.  The water pressure makes the doors hard to open, and a floating car can easily turn over in a flooded creek or ravine, trapping you inside.

3.     It is hard to judge the depth of water over a road, especially at night.  Also, the water may have washed the road away.

4.     Flood waters can rise quickly.  Water six inches deep can become two feet deep in a matter of seconds.

5.     In some states there is a hefty fine for ignoring a “road closed” sign, and some local governments require victims to pay for their own rescue from floodwaters. 

So what to do?  The answer is pretty simple.  If you come to a flooded road, turn around and go another way.  It’s better to lose a few minutes than lose thousands of dollars, and perhaps even your life.   

Nick.,
Please help settle an argument concerning heat lightning. I say that there is no such thing as heat lightning. Isn’t what everyone calls heat lightning just a reflection of lightning that is being generated somewhere?
Thanks,
Herb
Jackson, TN  

Herb,
You’re right; heat lightning is not really any different from regular lightning, but rather a name that people have given to various forms of normal lightning.  The usual form of heat lightning occurs when the lightning-producing thunderstorm is so far away that the air is clear overhead.  Because of that, it appears that the lightning is coming out of nowhere.  Actually it comes from the anvil of the distant thunderstorm, the top of the cumulonimbus cloud.  The false notion that simply heat can cause lightning may come from the fact that summer thunderstorms are often preceded by very hot and humid conditions.   

I hope this helps settle the argument!

Nick Walker
 

Hi Nick. When there is a thunderstorm and you are in it, what should you do to keep safe?
Emily
Bethlehem, PA  

Dear Emily, 

You obviously already know that thunderstorms can be dangerous.   Severe storms can produce damaging wind, large hail and even sometimes tornadoes.  But every thunderstorm is potentially dangerous simply because of lightning. It kills more people on average every year than tornadoes and hurricanes combined.  About one hundred people die from lightning annually in the United States, and hundreds more suffer lifelong injury or disability.  In fact, the National Weather Service calculates a one-in-three hundred chance that you or a family member will be struck by lightning sometime during your lifetime. 

But you don’t need to be afraid.  The simplest way to avoid danger is to get inside a home or other sturdy building during a thunderstorm.  Do it immediately; don't wait for the rain to fall.  Most lightning injuries occur before the rain starts and after it stops.  Remember, if you hear thunder, lightning is close enough to strike you.   

Lightning injuries are rare indoors, but to be safe, don't talk on a corded telephone, don't take a bath or shower, and don't use electrical appliances.   If lightning strikes outside phone lines, electrical wires or pipes, the electrical current can travel indoors.  Also, never watch lightning from an open door or window.  It's almost as dangerous as staying outside. 

If you are caught outside during a thunderstorm with no buildings nearby, you should avoid open fields, beaches, lakes and swimming pools.  Lightning often strikes the tallest object around, and you don't want that tallest object to be you.  That's also why isolated trees, picnic shelters and covered bus stops offer no protection, and may actually increase your chances of being struck.  If no other shelter is nearby, get into a car with metal sides and roof and roll the windows up.   

If no building or car is available and you must stay outside during the thunderstorm, find shelter in a dense woods or thick grove of small trees.   If you are trapped in an open space, get as low as you can in a valley or ravine and crouch down.  Stay away from metal fences, metal bleachers, flag poles and lamp posts. With some pre-planning and by following some simple rules, you can avoid the danger of nature's light show, and enjoy its beauty instead. 

For more on thunderstorm safety from the National Weather Service, go to their agency’s lightning safety pages at  www.lightningsafety.noaa.gov/ 

Nick

Nick,
I am 13 and I was wondering about something.  In a thunderstorm, is it safer to use an umbrella or not?   In my opinion is it is worse because you are making a bigger target for the lightning.  On the other hand, the umbrella will keep the rain and hail off of you.
Diana

You are right.  An umbrella will make you a bigger target for the lightning.  Also, a pointy tip will increase the electric field and increase the danger from lightning. 

Lightning is extremely dangerous, killing dozens of people every year.   Whether you have an umbrella or not, and whether it’s raining or not, if you hear thunder or see lightning you should immediately go indoors.  If you can hear the thunder, the lightning is close enough to strike you.  If you can’t find a building to go into, get inside a car, though a building is much better.  If you can’t find shelter, find an open space away from trees.  Squat down and minimize your contact with the ground.

Once indoors, avoid using faucets, sinks, bathtubs or showers.   Lightning may strike water pipes, and the strong electrical current can travel through them into a house.  Also, don’t use a corded telephone or any electrical appliances.   If lightning strikes the phone or power line, the electricity can travel through the line to you. Now and then, lightning can even come through windows, so stay away from them too.

Lightning is a beautiful wonder of nature, but treat it with respect. 

Nick

Dear Nick,
At work a question came up about lightning. I grew up in Florida and I was remarking about how a thunderstorm seemed much louder there than in Indiana where I live now.  Also, thunderstorm clouds in Florida seemed to be lower to the ground than in Indiana.  Is this correct?
Kimberly 
Elkhart, Indiana 

Kimberly, 
Your question intrigued me and I asked our severe weather expert, Dr. Greg Forbes for his opinion.  Like me, he is not sure if thunder is actually consistently louder in Florida, but he tells me that as a rule, the bases of clouds are probably higher in Indiana than in Florida.   This is due to higher humidity in Florida caused by the influence of the Atlantic Ocean and the Gulf of Mexico.

There are a number of factors that would influence the loudness of thunder.  One is the distance the hearer is from the lightning.  Since lightning is more frequent in Florida than in Indiana, Dr. Forbes says that perhaps it's just a matter of having lightning nearby more often in the Sunshine State. The sound of the thunder drops off by a factor of about four as the distance doubles.  So lightning that strikes three miles away from you will produce thunder about four times as loud as lightning six miles away.

Dr. Forbes thinks another factor could be the surface wind. Winds can bend (refract) sound waves. This bending can make it harder to hear thunder from more distant storms. In general, it is probably windier on thunderstorm days in Indiana than in Florida, and that could sometimes cause the thunder to be muted.

According to Dr. Forbes, there could be other factors in how loud thunder is, such as the height of the lightning charge centers and the intensity of the lightning discharges, but there’s no data on whether or not these would be consistently different between the two states.

Hello Nick,
I'm interested in knowing the speed of lightning as well as the temperature of lightning.
Hope
Pennsylvania

Dear Hope, 

Lightning is extremely fast and extremely hot.  Lightning is electricity, and as you know from turning on a light switch, electricity acts fast.  But unlike electrical wire, air is not a very good conductor of electricity, so it travels slightly slower through the air.  When electrical charges build up in a thunderstorm cloud, the positive and negative electrical charges in the cloud separate from one another.  The negative charges drop to the lower part of the cloud and the positive charges stay in the middle and upper parts.  Positive electrical charges also build on the ground below.  When the difference in the charges becomes large enough, a flow of negative charges moves through the cloud, or from the cloud down to the ground.  This is called a “stepped leader,” and travels at a speed of about 360 thousand miles per hour or one hundred miles per second.  When the positive charges leap upward to meet the negative charges, the jagged downward path of the negative charges suddenly lights up with a brilliant flash of lightning.  This stroke is much faster, from 180 million to 300 million miles per hour.  This flow of electrical charges and return stroke takes a fraction of a second, about two-tenths of a second in all.  It’s a hot bolt of lightning.  The temperature of lightning is estimated to be up to 50,000 degrees F, much hotter than the surface of the sun! 

Nick

Nick,
Where did the term "tornado alley" come from and how far is it?
Nicoia from Illinois

Dear Nicoia,
Tornado alley refers to the part of the United States that is more prone to tornadoes than other parts.  It includes portions of Texas, Oklahoma, Kansas and Nebraska.  They get more tornadoes here than anywhere else in the country (and anywhere else in the world, for that matter) because these states are in the perfect spot to get warm moist air from the Gulf of Mexico, cold air from Canada and dry air from the west.   When that combination comes together, as it does quite often in this area, the air can become unstable, and that makes conditions ripe for a tornado to form.  Severe weather expert Dr. Greg Forbes tells me that during the period between 1989 and 1998 those four states (TX, OK, NE, KS) averaged 355 tornadoes per year out of the national average of 1165.  That’s thirty percent of all tornadoes annually. In addition, those four states are usually in the top six in the number of tornadoes over a period of years, Florida and Colorado being the other two. 

Nick

What is the difference between a tornado warning and a tornado watch?
Ms.Echols
Illinois School for the Visually Impaired
Jacksonville, IL  

Dear Ms. Echols,
A watch is issued well in advance of a severe weather event to alert the public of the possibility of a tornado (tornado watch), severe thunderstorm (severe thunderstorm watch) flash flood (flash flood watch), or winter storm (winter storm watch). If you are in a watch area, please monitor your local weather throughout the day to see if severe weather develops.

A warning is issued when severe weather has developed, is already occurring and reported, or is detected on radar. If a tornado has been spotted by the public or law enforcement, or if a thunderstorm capable of producing a tornado has been detected by radar, the local office of the National Weather Service will issue a tornado warning. If a thunderstorm has developed that is capable of producing wind speeds of 58 miles an hour or greater or hail 3/4 of an inch in diameter, or perhaps a tornado, a severe thunderstorm warning is issued. If you are in the area under a warning, you should act immediately to get to a safe place. In the case of a tornado, get to an interior room on the lowest floor of your home or other building, and stay away from windows.