Questions for Jon Kahl

Learn more about my research In October 2008, John Kahl answered visitors questions about weather expert.

Your Comments, Thoughts, Questions, Ideas

bryan kennedy's picture

What is your favorite place to study weather? I've been to some places with unique climates and weather patterns. Do you have a place on Earth that interest you most?

posted on Tue, 10/07/2008 - 5:03pm
Jon Kahl's picture
Jon Kahl says:

I like places where the weather changes frequently. A tropical paradise, like Hawaii, is wonderful but it hardly ever changes. I prefer locations on the interior of large continents. In Kansas and Oklahoma, for example, people experience bitterly cold winters and hot, humid summers. Exciting weather, like thunderstorms and tornadoes, occur when the cold air masses come in contact with the warm ones,

posted on Sun, 10/12/2008 - 7:51pm
Joe's picture
Joe says:

What inspired you to pursue a career in atmospheric science?

posted on Wed, 10/08/2008 - 11:55am
Jon Kahl's picture
Jon Kahl says:

I decided on a career in meteorology rather late, after I had already completed a bachelor's degree in psychology at the University of Michigan. One night I went through my notebooks from all the college courses I had taken, and realized that the one meteorology course I had taken was my favorite. The next day I went to the Atmospheric and Oceanic Science department and applied for their graduate program.

posted on Sun, 10/12/2008 - 7:55pm
From the Museum Floor's picture

Why is it when there are tornadoes everyone says that the sky looks green?

posted on Wed, 10/08/2008 - 11:56am
Jon Kahl's picture
Jon Kahl says:

Many people have reported that the sky appears green during lightning flashes, especially during severe storms. The reason for the green color isn't completely understood. Sky colors are caused by the scattering of light by air molecules and other particles floating in the air, like dust and cloud droplets. When a stormy sky is illuminated by lightning, a combination of dense clouds of tiny water droplets with brief, intense flashes of light can cause the green color that has been reported.

posted on Sun, 10/12/2008 - 8:04pm
jimh's picture
jimh says:

I read that pollution from weekday traffic affects the weather on the weekends. How does that happen?

posted on Wed, 10/08/2008 - 12:22pm
Jon Kahl's picture
Jon Kahl says:

Since more people drive to work on weekdays as compared to weekends, there tends to be more pollution in urban areas on the weekdays. The pollution prevents some sunlight from reaching the ground, and can cool the temperatures. Also, the pollution makes it more likely for precipitation to form, because cloud droplets need particles in order to form. Rain can also cool the temperatures.

posted on Sun, 10/12/2008 - 8:15pm
ulla's picture
ulla says:

how is hail made?

posted on Wed, 10/08/2008 - 2:58pm
Jon Kahl's picture
Jon Kahl says:

Hail forms when raindrops fall through a turbulent thunderstorm. The turbulence contains strong winds moving straight upward, called updrafts, which carry raindrops up to high altitudes within the storm. At high altitudes the drops freeze, and and fall back towards the ground. Sometimes this cycle repeats many times, causing the hailstone to grow larger as it bumps into thousands of other raindrops.

posted on Sun, 10/12/2008 - 8:24pm
Faith's picture
Faith says:

Why does weather change?

posted on Thu, 10/09/2008 - 5:56pm
Jon Kahl's picture
Jon Kahl says:

The atmosphere is always moving. As it moves, it carries heat from the warm places towards cold places. In this way, the atmosphere helps prevent the equator from getting warmer and warmer due to the large amount of sunlight it receives. It also helps prevent the north and south poles from getting colder and colder. Changing weather shows you that the atmosphere is doing its job, spreading heat around the entire planet.

posted on Sun, 10/12/2008 - 8:32pm
sam kast's picture
sam kast says:

hi john!!!!!

my queston is why do we have wether on earth and how does it affect us?

posted on Fri, 10/10/2008 - 4:02pm
Jon Kahl's picture
Jon Kahl says:

We have weather because the atmosphere moves air around the entire earth, making some places warmer and wetter while others get colder and drier. The weather affects many different aspects of our lives. In warm areas like the tropics, many houses don't have windows. Weather affects the clothes we wear and the food we eat. Weather also affects the jobs people have. For example, they don't have many snowplow drivers in Hawaii!

posted on Sun, 10/12/2008 - 9:01pm
julia mak's picture
julia mak says:

how are hurricanes formed?

posted on Sat, 10/11/2008 - 10:10am
Jon Kahl's picture
Jon Kahl says:

Hi Julia! Hurricanes are enormous storms that form over warm ocean waters. They form in the tropics, the part of the earth that's close to the equator. (If you look at a globe you'll see that in the tropics, most of the earth is covered by oceans.) The intense heat of the sun shines down on the ocean and evaporates a lot of water. As the water vapor (evaporated water) rises into the atmosphere, huge amounts of heat are released into the air, causing a cluster of thunderstorms. At this point the storm is called a 'tropical disturbance'. As the storm strengthens and begins to rotate, it becomes a 'tropical depression' and then a 'tropical storm'. When wind speeds reach 75 miles per hour the storm is called a hurricane.

posted on Mon, 10/20/2008 - 8:18am
CoreyJo's picture
CoreyJo says:

Haven't forest fires been happening throughout the earth's life? If so why would the soot be doing more damage to Greenland's snow now?

posted on Sat, 10/11/2008 - 10:36am
Jon Kahl's picture
Jon Kahl says:

You're right CoreyJo, forest fires have been around for a long time. When forest fire chemicals like soot are detected in Greenland's snow, we know that the winds carried air from northern Canada or Siberia, large regions with a lot of forests. The winds also carry pollution from cars and factories in these regions. So the soot tells us that other pollutants may also be present in the snow. Soot is also important because it makes the snow darker. Darker snow absorbs more sunlight, causing it to melt faster. This is a problem now, as you noted. But by analyzing soot in Greenland ice cores (snow from past years), we can get an idea of how fast snow melted in the past.

posted on Sun, 10/12/2008 - 9:07pm
Anonymous's picture
Anonymous says:

It seems like winters in the midwest are getting milder - both warmer and less snow. Is that something that is backed up by any data or is it just perception and things are about the same as they usually are?

posted on Wed, 10/22/2008 - 3:19pm
Jon Kahl's picture
Jon Kahl says:

Yes, it's true. During the 20th century, temperatures have warmed by about 4 degrees Fahrenheit in the northern portion of the Midwest, and by 1 degree in the southern portion. Annual precipitation has increased as much as 20% in some areas.

posted on Thu, 10/30/2008 - 1:58pm
Anonymous's picture
Anonymous says:

I know that wind chill is calculated differently now than it used to be - what's the difference and why did they change it?

posted on Wed, 10/22/2008 - 3:20pm
Jon Kahl's picture
Jon Kahl says:

The earlier wind chill formula was developed in 1945 by Antarctic explorers Paul Siple and Charles Passel. By suspending plastic buckets filled with water from a pole, they measured heat loss due to the combined effects of cold temperature and wind. The wind chill equivalent temperature formula was based on Siple and Passels' work.

The earlier wind chill formula was rather simplistic. It lumped the heat loss processes of radiation and convection together, it ignored some of the thermal properties of human skin, and it assumed that the wind was measured at a height of 10 meters rather than at the height of a human face. The new formula was adopted by the U.S. National Oceanic and Atmospheric Administration in 2001. The new formula for winds in mph and Fahrenheit temperatures is:

Wind chill temperature = 35.74 + 0.6215T - 35.75V (**0.16) + 0.4275TV(**0.16).

In the formula, ** means the following term is an exponent.

posted on Thu, 10/30/2008 - 2:27pm
Anonymous's picture
Anonymous says:

Why does the US use farenheight and the rest of the world celcisus? Do any other countries besides the US use farenheight?

posted on Wed, 10/22/2008 - 3:21pm
Jon Kahl's picture
Jon Kahl says:

Only three countries use Fahrenheit as the official unit of temperature measurement: the United States, Burma and Liberia. The United States is the only industrialized country in the world that doesn't predominantly use the metric system. The metric system, including Celsius for temperature measurement, is widely used in the United States in the fields of medicine, science and engineering. There have been several attempts to completely switch to the metric system, but they have not been successful.

Why doesn't the United States switch to the metric system? I think most people are comfortable with the old system, and sometimes it's difficult to convince people to change.

posted on Thu, 10/30/2008 - 2:51pm
Anonymous's picture
Anonymous says:

Have you ever been in a hurricane?

posted on Wed, 10/22/2008 - 3:23pm
Jon Kahl's picture
Jon Kahl says:

Unfortunately, yes. As much as I enjoy observing different types of exciting weather, being in a hurricane was not fun. I was in Cancun, Mexico in November 2005 as Hurricane Wilma churned toward the Yucatan peninsula. As it approached Cancun, Wilma became the strongest hurricane ever observed in the North Atlantic Ocean. I was attending a conference, and we just barely made it out of town before the Mexican army forced everyone to leave the hotels and move to shelters. I learned later that the hotel where I had stayed was flooded up to the third floor!

posted on Thu, 10/30/2008 - 3:04pm
Anonymous's picture
Anonymous says:

Do you think global warming is human caused or part of a large climate cycle? How do you think it is impacting our weather?

posted on Wed, 10/22/2008 - 3:28pm
Jon Kahl's picture
Jon Kahl says:

I think greenhouse gases put into the atmosphere by humans are contributing to global warming. I also know that climate changes naturally even without the help of humans. The big question is: what portion of climate change is due to human activities? This is an extremely difficult question to answer, because we can't just run an experiment in a laboratory to figure it out (the earth and the atmosphere *is* our laboratory!). Many people have very strong opinions about this question, but we really don't know the answer yet.

Regardless of the causes, the earth's climate has definately been changing. Most areas are getting warmer. Most of the warming has occurred at night. Also, there have been increases in extreme weather: more heat waves, cold spells, droughts and floods.

posted on Thu, 10/30/2008 - 3:09pm
grace hillmyer's picture
grace hillmyer says:

What is acid rain?

posted on Sun, 10/26/2008 - 2:29pm
Jon Kahl's picture
Jon Kahl says:

Hi Grace. Acid rain is air pollution that comes out with the rain or snow. When pollution enters the atmosphere from factory smokestacks or automobile exhaust, the winds carry it long distances in the atmosphere. Eventually, the polluted air enters a cloud that produces rain or snow. With acid rain, the pollution often leaves the air hundreds of miles away from its source.

posted on Thu, 10/30/2008 - 3:15pm
Matt's picture
Matt says:

What's the record for the most snow in a month?
Can water remain liquid below 32 degrees?



posted on Sun, 10/26/2008 - 3:43pm
Jon Kahl's picture
Jon Kahl says:

Hi Matt:

The U.S. monthly snowfall record is 390 inches, Tamarack, Calif. Jan. 1911. The world record for seasonal snowfall: Mount Baker Ski Area, near Bellingham, Washington, 1998–1999: 1,140 inches of snow.

And yes, liquid water can exist at temperatures below 32 degrees Fahrenheit. Supercooled water, as it's called, has the interesting property that it freezes instantly when it comes in contact with a frozen object. This is why ice cubes feel 'sticky' when you touch them in your freezer. The water in the skin of your fingers becomes supercooled while your hand is in the freezer, and it freezes when it touches the frozen ice cube.

posted on Thu, 10/30/2008 - 3:25pm
Blaze's picture
Blaze says:

What is exactly happening when it is hailing and what is happening when it is snowing.
Whats the difference?

posted on Wed, 11/05/2008 - 2:06pm
Jon Kahl's picture
Jon Kahl says:


Precipitation takes the form of snow when the temperatures of the air in the cloud, the air at ground-level, and the air in between are all below freezing. Hail, on the other hand, occurs when falling raindrops are carried upward to high altitudes within a turbulent thunderstorm. The temperature at these high altitudes is well below freezing, so the drops freeze, and fall back towards the ground. Sometimes this cycle repeats many times, causing the hailstone to grow larger as it bumps into thousands of other raindrops.

posted on Sat, 11/08/2008 - 4:28pm