Such updrafts help to produce hail - balls of ice that in the strongest storm can be larger than baseballs. Imagine what happens to the windshield of an airplane that is hit by several such hailstones. Of course, in such a thunderstorm severe ice accumulations could bring down an airplane before it has a chance to run into hail.
Surprisingly, little mention is usually made of the reason that thunderstorms are called thunderstorms - lightning.
Without lightning there's no thunder. The lighting flash that you see is an electrical current which might be 100,000 amperes. It's hot - 50,000 degrees Fahrenheit or higher. Lightning's sudden heating of the air causes the air around it to expand. When the stroke ends, the air cools and contracts. This creates the sound waves that we hear as thunder.
You might think that a 100,000-ampere electrical current that can heat the air to 50,000 degrees would fry anything that came near it, including an airplane. Fortunately, this isn't the case.
During the 1980s a NASA F-106B flew into 1,400 storm clouds, getting hit by lightning at least 700 times with no serious damage while collecting data that's still used to help protect aircraft.
On average, lightning strikes each commercial airliner in the United States once a year. Yet, the last U.S. airliner crash blamed on lightning was 38 years ago.
On December 8, 1962, lighting hit a Pan American Boeing 707 that was flying a holding pattern over Elkton, Maryland, igniting fuel vapor in a tank - causing an explosion that brought the plane down, killing all 81 aboard. Edward Rupke, a senior engineer at Lightning Technologies, Inc. in Pittsfield, Massachusetts, says that it had been generally believed that an airplane made of aluminum, which is a very good electrical conductor, was in no danger from lightning because the current flows along the airplane's skin and into the air.
This is true and is essentially why lighting doesn't regularly knock aircraft out of the sky. But, as the 1963 crash showed, there's more involved than relying on aluminum's being a good electrical conductor.
The 1963 accident "woke people up," says Rupke, and "resulted in a substantial increase in safety." At the time, federal aviation regulations governing aircraft construction didn't mention lightning. "With that accident the FAA started writing rules for lightning protection. More attention was paid to the design of fuel systems."
A key is ensuring that lightning won't cause sparks in the fuel system, such as by making sure joints and fasteners are snug enough that sparks won't jump between them. The skin around fuel tanks has to be too thick for lightning to burn through.
As more and more aircraft and aircraft structural parts are built using composites, some of which don't conduct electricity, designers have had to come up with ways to make them conductors, such as by adding metal.
Rupke's company uses simulated lightning bolts to test composite panels or entire small aircraft and has found that lightning can seriously damage unprotected composites. He advises pilots of fiberglass or composite aircraft that aren't designed for lightning protection not only to stay far away from thunderstorms, but also not to fly through other clouds because the clouds could have enough electrical charge in them that the aircraft could trigger a lightning flash. He mentioned a glider in the United Kingdom that came apart in the air after lightning hit it. "Both people in the glider [survived] because the club that owned it required those flying in it to wear parachutes," Rupke said.
When you see a flash of lightning it almost always flickers. This is because lighting is usually like an electrical current that's being turned on and off much faster than any human could flick a switch. This on-and-off current can cause problems with aircraft electrical and electronic systems.
For the 1980s lightning flights, NASA equipped the F-106B with an array of instruments to capture immense amounts of data. NASA says that these instruments recorded more than a million individual measures from each lightning stroke that hit the airplane.
One of the findings was that multiple-burst strikes induce a lot of random electric currents into the airplane, which produce rapidly changing magnetic fields. This is not the kind of thing you want going on in one of the new airplanes that use "fly by wire" systems. The NASA research prompted the FAA to begin requiring in 1987 that flight-critical electronic systems be protected against lightning.
Of course, the FAA regulations for lightning protection of general aviation airplanes are more basic than those for Transport category aircraft with "flight-critical" electronic components. Since most general aviation airplanes are made of aluminum and few have computerized engine and flight controls, lighting isn't as much of a danger as it could be to the latest transport.
Most of the time, other thunderstorm hazards such as extreme turbulence are more of a danger to small aircraft. That should be more than enough reason to stay far away from a cloud that could also zap your airplane with a lightning bolt.
In fact, for general aviation pilots who don't fly into thunderstorms, lighting could be a bigger danger on the ground than in the air.
Lightning tends to be underrated as a weather killer because most of its victims die one at a time rather than in big events such as tornados that draw the television cameras. From 1971 through 2000 lighting killed an average of 73 people a year in the United States, compared with an average of 69 tornado deaths and 16 hurricane deaths. And, researchers suspect that lighting deaths are underreported.
The basic lightning safety rule on the ground is to take shelter in a vehicle or a sturdy building - not an open-sided shelter like those found on golf courses - and certainly not under a tree. A vehicle, including an airplane - as long as it's not a composite airplane - is a safe shelter, but not for the reason that many people think. The vehicle's tires do not "insulate" it from being hit by lightning. A lightning bolt that's traveled through a couple of thousand feet of air, which is a very good insulator, is not going to be slowed by an eighth of an inch of rubber. Instead, a metal car or airplane acts like a "Faraday cage" in which the lightning's electrical current travels though the vehicle's or airplane's skin and then jumps to the ground. Sometimes the lighting jumps to ground through a tire, blowing it out.
This is why the last place you want to take shelter from the rain in a lightning storm is under an airplane's wing. You'd offer lighting a quick path to the ground.
Rupke comments that airline ramp workers who are standing near an airplane with a headset plugged into the aircraft are in great danger if lightning hits the airplane. "We lose one or two people a year from electrocution while they are standing outside of airplanes."
Lightning safety experts have a rule that applies whether you are playing softball or on the ramp at an airport: "If you see it flee it. If you hear it clear it."
Jack Williams is the weather editor of USAToday.com. An instrument-rated private pilot, he is the author of The USA Today Weather Book and co-author with Dr. Bob Sheets of Hurricane Watch: Forecasting the Deadliest Storms on Earth.
