Dr. Jon Nese

    Dr. Jon Nese
    The weather
    February 8, 2001

    Benjamin Franklin once said, "Some are weatherwise, some are otherwise." It's as though he was talking about Dr. Jon Nese, Chief Meteorologist at the Franklin Institute. Asking about the weather may seem like small talk to you, but at the Franklin Institute they take the matter seriously. Dr. Nese is responsible for the day-to-day operation of the weather station at the Institute located in Center City Philadelphia. The center is both an operational forecast facility and an exhibit. Visitors to the Institute can learn about the atmosphere and the atmospheric conditions that create our weather.

    Up-to-the-minute weather data in an easy-to-understand way is Nese's claim to fame. With the help of NBC-10, the Institute presents the NBC-10 Earthwatch Weather Workshop program. Dr. Nese and the NBC-10 Earthwatch meteorological team collaborate and co-present these workshops in Musser Theater. If you're in the area you can catch his presentations at the Franklin Institute or tune your radio to WHYY or NPR to hear Dr. Nese's daily forecast.

    The topic of the workshop is tied to the season of the year; summer and fall is "Hurricanes," winter is "Winter Storms," and spring is "Tornadoes and Thunderstorms."

    Inside the Weather Center you can check out the latest satellite and Doppler RADAR images, look at Philadelphia weather data back into the 1800s, and see "barometer number 1," the air-pressure measuring instrument used by The Franklin Institute's first meteorologist in the 1830s.

    Dr. Nese received his B.S. in Meteorology in 1983 and Ph.D. in Meteorology from Penn State in 1989. He was a professor at many of the satellite campuses teaching Meteorology as well as Earth Sciences, Algebra, and Calculus. Pennsylvania climatology is one of his main interests.

    An Updated Tornado Climatology of Pennsylvania is one of Nese's many contributions to the study of weather which appeared in the Journal of the Pennsylvania Academy of Science recently. Dr. Nese also co-authored A World of Weather: Fundamentals of Meteorology, a textbook and lab manual for introductory meteorology.

    For more information on the Franklin Institute programs visit http://www.fi.edu/index.html. For fun weather facts and activities, go to http://www.fi.edu/weather/index.html.


    US Today we're speaking with Dr. Jon Nese, Chief Meteorologist of the Franklin Institute. Dr. Nese runs the day-to-day operation of a weather station at the institute, which is located in Philadelphia. The weather center is both an operational forecast facility and an exhibit at the institute, where visitors can learn about the factors that create weather. Dr. Nese's forecast can also be heard daily in Philadelphia on the radio station WHYY. Some background on Dr. Nese: He graduated from Penn State with a B.A. in Meteorology in 1983 where he received his Ph.D. in 1989. I would like to welcome all the schools across the country that are joining us particularly our friends in Texas and California. Please be advised that we are working with a 30-second delay which means when you ask a question I will get to it 30 seconds later. Believe me I am not ignoring you — I will get to as many of your questions as I can. During the course of the interview, you'll see on your computer screen weather-related images. One last word: This session will be archived. So please be sure to visit the site again and read what we have here today. Welcome Dr. Nese.
    Nese Hi there.
    US How is the weather where you are?
    Nese Well, it's a lot better than it was on Monday when we had four inches of snow here in Philadelphia and some of our northern suburbs got a foot.
    US Well, our company is actually outside of Philadelphia, and we all kind of got hit by this surprise snowstorm, and many meteorologists in the area expected far less snow than we received. With the all your fancy tools, how did this happen?
    Nese Oh yeah, rub it in. Well, meteorology remains a bit of an inexact science. The problem on Monday was really a matter of one or two degrees in four hours. And by that I mean, the atmosphere cooled one or two degrees more than most meteorologists expected on Monday afternoon, and that allowed the snow flakes, which were falling, to stay snow, instead of melting into rain drops. Secondly, by four hours, I mean that the cooling took place around noontime on Monday instead of 4:00 or 5:00 in the afternoon. So even though we do have a lot of fancy tools and computer models, sometimes small differences like that in temperature or time, turn out to be a huge difference in the actual weather that people experience. And I'm sure you'll agree that's what happened on Monday. Also the problem with timing and the problems with temperature, occurred at absolutely the worse time of the day to inflict human misery, and that's what it did on Monday afternoon in the Philadelphia area.
    US It sure did. Do you foresee a period in the near future where you'll be able to predict the small degrees of temperature difference, say 24 hours in advance?
    Nese That's a good question. In the future, yes. In the next five years? Not every time. In the next ten years? No, not every time. I think the percentage of time that we will be able to catch those small differences will slowly increase. But I do not foresee a time in the next, 5, 10, 20, even 30 years, where we get it right all the time.
    US Ok. Well, we'll carry umbrellas till then.
    Nese Okay.
    US How did you become interested in meteorology?
    Nese I get asked that a lot, and my first recollections are my father was a baseball coach and he let his little 8-year-old son sit on the bench and keep score and this was a high school team, so this was a big honor. So of course I never wanted the games to be rained out. And so I would literally sit in front of the television the night before, and this was before the time of remote controls, and I would literally twist the dials between channels 11 and 3, and 2, which were the big stations where I grew up, and literally wear out the dial, twisting back and forth. So I was blamed for ruining many a television dial.
    US Can you tell us what you do at your weather center, and I know this is a broad question, but how do you predict the weather?
    Nese Well, predicting the weather is only a small part of what I do. We do supply national weather forecasts for national public radio here in Philadelphia. Let me just briefly mention that I also do some television work for the public broadcasting station here. So I do a little one-minute weather piece every night on the evening news. I give tours of my office here, which is a mini-weather station. I'm writing a book about Philadelphia weather that should come out in early 2002 — so weather forecasting is just a small part of what I do. As far as forecasting goes, anybody who ever wants to forecast anything, starts by observing what's the thing that you want to forecast is doing right now. So observations are key. And by observations I mean, temperature, pressure, humidity, wind, cloud cover — not only at the ground-but high above our heads, and then of course satellites, radar, and any other kind of observations we can get at the beginning. So it all starts with observations.
    US Okay. Is this something anyone can do?
    Nese Well, most of the observations that we meteorologists look at are now available on the web. So most- if you have access to the web, you can get the data. Now, then comes the interpretation part. Meteorologists learn how the atmosphere works. We learn why certain patterns of temperature, pressure, and wind produce certain types of weather, and then we learn the laws or the equations that govern how the atmosphere will change from the way it looks now, to the way it will look 6 hours from now, and 12 hours from now, and 36 hours from now. So that's part of the meteorologist training, understanding the atmosphere. Then, it really is, as in so many other fields, the more experience you have forecasting, the more times you've seen certain situations, generally speaking, the better forecaster you are. In addition, you start to learn the nuances of a local area. How does that nearby lake affect our weather? What about those mountains 50 miles to the Northwest? What happens when the wind is blowing across those mountains? So subtle local influences also play into it. And then finally, meteorologists depend heavily, these days, on computer models. We literally program computers to forecast the weather and then use that guidance to shape our forecast.
    US Fabulous. I just would like to interrupt you for a minute, Dr. Nese, to welcome all those who have just joined us. Lula. Keith Parker. Folks from Texas. Thank you for joining us. Again feel free to ask any questions that you have. Um, Dr. Nese, you said you're writing a book about Philadelphia weather?
    Nese Yes.
    US What's going to be in there?
    Nese Well, I'm writing the book with one of the local meteorologists here in Philadelphia. We're looking at the history of the city of Philadelphia, where it fits in the weather history of this country. You know, a lot of people are aware of where Philadelphia fits in the American history story. Independence Hall. Declaration of Independence. Washington crossing the Delaware, the Liberty Bell. These are all familiar to most Americans. But most people don't know that if you want to describe the history of weather science in the United States, it also passes right through Philadelphia, and in fact it passes right through the organization that I work for, the Franklin Institute. So we're going to devote a chapter to that. A chapter to basic weather principles — fronts, jet streams, what you see when you see the evening weather report. And then one chapter to each season, winter, spring, summer and fall. And then we're going close out with a discussion of these global topics, like global warming, and what does it mean to you and me. And what might the climate be like around here, 50, 75 years from now.
    US I'm glad you mentioned the word "climate" Dr. Nese. What is the difference between weather and climate?
    Nese Climate is generally defined, if you want to give it two words, as average weather. So, whereas weather refers to a day-to-day variation of conditions in the atmosphere, climate refers to average conditions. So for example the average amount of snow fall that would fall in January is a climate piece of information. It does not necessarily say how much snow in a particular January but it gives you a sense of what the average is. So climate includes averages and also information about how much deviation you tend to find away from the average.
    US Ok. Ok. We've just gotten a question in from Jason in Pennsylvania; it's a serious one so I think I have to ask it. He writes, "I'm reading about the Coriolis Effect in school. What is it? I don't understand."
    Nese The Coriolis effect is one of the more difficult meteorology concepts so I definitely understand the confusion here. The best way to describe the Coriolis effect is to imagine, and this is an analogy, that is not necessarily exactly how the Coriolis effect works, but imagine taking off on a rocket ship launched from the equator and flying toward the North Pole.
    US Uh-huh.
    Nese Now while you're in the air, the earth is rotating beneath you. You need to account for the fact that the earth is rotating beneath you as you plot your course northward. Essentially, the point to take from that is: the rotation of the earth affects the direction of movement of any object moving across the earth's surface. Now what does that have to do with the weather? Well think of the wind as something that moves across the earth's surface and therefore the Coriolis effect, which essentially comes from the rotation of the earth, affects the direction that the wind blows.
    US Dr. Nese, not surprisingly, a lot of our students have an interest in wild weather, and have several questions about hurricanes, and tornados, and cyclones. Can you tell us first, what is the difference between a hurricane and a tornado?
    Nese Well that's a great question because it's one I get a lot. I would say the best answer to that is to say they only have about one thing in common, and that's that they both are characterized by strong winds. That's about the only thing that tornados and hurricanes have in common. Hurricanes are large storms that develop over warm ocean water. A typical hurricane might measure 2-3-4 hundred miles across and a hurricane's most distinctive feature, as I'm sure that many students undoubtedly know, is the eye. The center of the hurricane is an area of relative calm in the storm. So a hurricane is a big storm, hundreds of thunderstorms working together. Heavy rain, strong winds. To officially be characterized as a hurricane, it has to have winds of 75 miles per hour. A tornado on the other hand is a much smaller storm. Most tornadoes form over land. Tornados form from thunderstorms. You need to have a really nasty, nasty thunderstorm to get a tornado. Most tornados are relatively small, maybe a hundred yards in size, and they don't last very long. Maybe ten minutes would be a reasonable average. So there is a big difference between these two kinds of storms.
    US Dr. Nese, we just got a question from Juliet out in California. She asks, "What causes the eye in a hurricane?"
    Nese That's another great question, and another one that's not simple to answer. But I'll give it my best shot. Imagine in a hurricane, the hurricane is a low pressure system. If we had to represent a hurricane on a weather map, with one of those symbols, the "H's" or the "L's." Hurricanes are "L's". This means the wind around the hurricane tends to spiral in toward the middle and as it spirals in the winds winds tend to increase in their speed. Now, a wind -the wind on earth cannot achieve a speed of infinity. There has to be some maximum speed of the wind. So imagine the wind circling in toward the center of the low pressure getting stronger and stronger as it goes. It can't go right to the center because if it did, its speed would have to go to infinity. And that can't happen. What happens is the wind stops short of going right into the center and thus you get this zone of relative calm right in the middle.
    US That's amazing actually. Can two hurricanes run into each other?
    Nese Well, think of it this way. Hurricanes as we just said, are centers of low pressure. So between any two lows, let's think of it in terms of topography. If you have a valley over there, and another valley somewhere else, in order for them to be defined as valleys there has to be a hill in between, or you wouldn't have two valleys. In the same way, the atmosphere, if you have a hurricane over there, you have low pressure, and another hurricane over there, another low pressure. There has to be a zone of low pressure in between. Essentially they don't run into each other but sometimes they do get close enough to each other that one will weaken in favor of the other. But you would not see two hurricanes out in the ocean coming toward each other, and meeting or bouncing off one another. That would not happen
    US Okay. We just got a question from Dana who is out in Dallas, Texas. She writes that the meteorologists in the Dallas area, are expecting thunderstorms that may spawn tornadoes, how does that happen?
    Nese Well, strong thunderstorms tend to form when a huge mass of air of one characteristic, let's say warm and moist, meets another large mass of air of the opposite characteristics. Let's say cold and dry. And Dallas happens to be in a place where you do have access to warm moist air. It comes in on southeast winds off the Gulf of Mexico. And Dallas also happens to be in a place where you have access to cool dry air that comes down from the north. So what you're going to see in the Dallas area are these two air masses meeting. What happens when warm moist air meets cold dry air, the warm moist air rises over the cold dry air, (cold dry air is heavy) and when warm air rises you get thunderstorms. So Dallas is in a place, that's the southern end of tornado alley, where tornadoes are not uncommon.
    US How fast can winds move in a tornado?
    Nese The world record for winds measured in a tornado was measured on May 3, 1999 near Oklahoma City, and it was about 318 miles per hour. That's considered to be near the top of the wind speeds that you're going to measure near the surface of the earth.
    US Correct me if I'm wrong — that was an F5, right?
    Nese Yes, that was an F5.
    US Can you speak to how tornadoes and hurricanes are measured like that?
    Nese The particular measurement of the F5 tornado near Oklahoma City, was not made with a conventional weather instrument to measure wind speed. I'm sure many of the students know that's called an anemometer, measures the speed of the wind. That measure was taken with Doppler radar, which is a device that you can use from a distance. Radar is a weather instrument most people are familiar with for telling us where and how it's raining or snowing, and how hard its raining or snowing. The Doppler technology allows radar to measure the speed of the wind.
    US Have you ever chased a tornado or hurricane? Are you one of those storm chasers?
    Nese I'm one of those meteorologists who would prefer to let somebody else do the chasing.
    US I understand that before a tornado the sky turns green? Is that true? And if so, why?
    Nese Some people have reported the green sky phenomenon during severe weather. But I'm going to be honest with you here. I know that it is a matter of intense research, I do not think that the actual reason behind the greenness has been thoroughly explained. And I'm not familiar with that what that research is.
    US Okay. Are there different types of tornadoes?
    Nese Well, there are different intensities of tornadoes. You've already alluded to the fact that we use a scale, the "F scale," named after a professor that designed the scale at the University of Chicago; he passed away a couple years ago. He designed the scale around 1970. It ranges from 0 to 5. But another way to answer you question would be, I would like to think of tornadoes of having cousins, for example, a tornado that develops out over water, sometimes without a strong thunderstorm above it, is called a water spout. Also, little mini-tornadoes can develop without a thunderstorm on a hot day, a dry day, when the sun bakes the ground, and sometimes you can get the winds to twist a little bit much, like when they twist when wind develops over corners in a building. We call these dust devils. And in fact Benjamin Franklin was famous for chasing dust devils. This was very famous, some kids may have learned a legend about how he chased a tornado on horseback back in the 1700s? That was actually a dust devil that had developed over dry farm land in Maryland.
    US Speaking of Benjamin Franklin, a question has come in from Indy in New Hampshire. Who writes, "You are at the Franklin Institute. What was Franklin's role in weather forecasting?"
    Nese He certainly was the giant in meteorology during the 1700s, there's no doubt about it. As far as forecasting goes, Franklin was one of the first, if not the first, there's still some argument about this, but most scholars say he was the first to publicly say that the weather tends to move from west to east, or particularly storms -somebody in New Hampshire would be very aware of these nasty storms which we call "Nor'easters," which we had one on Monday — that they come up the east coast, that they originate from the south west and they move to the north east. Franklin actually recognized back in the 1740s, despite the fact that he didn't have observations from other places, he realized that that storm came from the southwest. So his biggest contribution to forecasting was probably recognizing the direction that storms move.
    US I have several other follow-up questions about Ben Franklin that I'd like to come back to. We had a question from John in Lacy (ph) in Washington who writes, "Why do we not experience serious or dramatic weather here in Washington State. Like hurricanes or tornadoes?"
    Nese Washington gets most of its weather from the Pacific Ocean. So such a large body of water tends to moderate the extremes, that is, during the winter, the ocean water doesn't get that cold. So when air comes in off the ocean, it's not that cold. During the summer on the other hand, the ocean water does not get very warm. So when air comes in off the ocean it's not very warm. So big bodies of water have a moderating affect on weather. Now if you live in eastern Washington, east of the Cascades, or far eastern Washington where it's very dry, it might be a slightly different story. Washington state doesn't get hurricanes because simply, you're too far from the equator. The only places that experience hurricanes would be much closer to the equator.
    US We have a question from Pete Parker, who I assume is not the real "Spiderman." At any rate he writes, "In Franklin's time what were some of the early methods of predicting the weather?"
    Nese Well, there weren't many. Folklore were some. The Pennsylvania Germans who populated this area during the 1700s, had dozens of folklore, which basically means they noticed certain relationships between nature and the weather, or the way animals acted and the weather, or phases of the moon and the weather. And came up with rhymes, sayings that they thought they would help.

    One that is still around is, rainbow in the morning, sailor take warning, rainbow in the night, sailor's delight. Essentially you can translate into saying that if you see a rainbow at night, the next day would tend to be fair. So it was really folklore.

    US I'd just like you to know, Dr. Nese, that we've been joined by two schools, one here from Michigan, another from Vermont. Actually we have individuals joining us with such screen names as "rain man" and "snowflake." Welcome to you all. When Dr. Franklin was putting together his Poor Richard's Almanac, and making all those predictions, did he just kind of make them all up?
    Nese Pretty much. I mean, there were certainly no way in the 1700s, nor is there any way today, to make weather predictions with any kind of detail more than a week or two in advance. This is one point I would like to be very clear on. The students may run into places where they see weather forecasts published in some detail for two weeks, three weeks, three months in advance. I get a lot of phone calls here at the museum, parents wanting to schedule their child's wedding on a particular weekend next May, and they want to know if I know what the weather will be like. And I say definitively, the answer is, there is no way we can know with any degree of accuracy what the weather will be like that far in advance. I can quote you statistics. I can tell you what the average high is for May 15. I can tell you on how many of the previous May 15ths it rained in Philadelphia. I can give you a statistical forecast. But there is no way where the highs and lows of weather will be on that day, this far in advance.
    US Now, I understand that Dr. Franklin also charted the gulf stream and that the gulf stream is what affects "el niño" and "la niña" and I understand this is a "la niña" year which is a very convoluted way of saying, can you tell us about "la niña" and "el niño"?
    Nese Let me clear something. The gulf stream has, the gulf stream has nothing to do with "el niño and "la niña". You had a couple points in there I'd like to clear up. The first one is the part about the gulf stream and you recognized that it was a current of warmer water and it did affect the travel time between the old world and the newer world. The gulf stream is an Atlantic phenomenon, which has nothing to do with "la niña" and "el niño."

    "El niño and "La niña" are the names we give to temperature anomalies in the water along the tropical Pacific ocean. It's close to the equator in the central and eastern Pacific ocean. "El niño is what we give when that patch of water is unusually warm and "la niña" is what we give when that patch of water is unusually cool. Sometimes the waters are really, really, warm and we say that was a strong "el niño. And sometimes they are very, very, cool, and we would call that strong "la niña." Right now we're in what would be termed a weak "la niña," the waters along the equatorial Pacific are slightly cooler than average.

    US Dr. Nese, what is Saint Elmo's Fire?
    Nese Well, let's just put it this way. It's an electrical discharge in the atmosphere that I'm not familiar with.
    US Okay. That's fine.
    Nese It's also the name of a movie that I liked a lot back in the early '80s I believe.
    US I liked that movie too. That was fabulous.
    Nese I think I remember the sound track, but I don't think you want me to sing it to you.
    US Do you have a nice voice? You sound like you have a nice voice.
    Nese I was in the third grade choir.
    US That's great. We got ... just before our server went down ... we got several questions about global warming and just broadly, I'll ask one that came in from Florida, first of all what is global warming, and do you think it's actually occurring?
    Nese Well, "global warming" is the name scientists give to an unnatural enhancement of the natural process called the "greenhouse affect." As many students know, there is a process called "greenhouse effect" which is actually a good thing. There are gases in our atmosphere made up of water vapor which have a very special property. They absorb energy that the earth emits and keeps some it from going into space. And that actually keeps the earth, about get this, 60, that is 6-0 degrees Fahrenheit warmer than it would be if these gases were not present. In other words, without the greenhouse affect, there would be no life on earth at least not as we know it. So the greenhouse effect is a good thing however, human beings put certain gases in the atmosphere, particularly carbon dioxide, which may be enhancing the natural greenhouse effect. And that's what we call "global warming." It's an unnatural enhancement of the warming process.

    Now, is it real? Good question. The consensus of the scientific community, of the best scientists doing the research, is that, yes in the last 100 years or so, the average temperature of the air near the surface of the earth has gone up a little bit. A degree, a degree and a half Fahrenheit. Now the question is, what is the cause? There are probably several causes, some may be just natural variability because the climate does go through some natural changes. But the consensus among the research community is that we human beings are responsible for at least some of that warming. And to make it an even stronger statement, if we continue to pump carbon dioxide into the atmosphere at the rate that we're currently doing it, then in the next century, the warming will increase. So that the projections that were just released, two weeks ago, by the international panel on climate change, which is an international group of perhaps two to three hundred scientists, the best scientists in the world, projects a warming of between 2 and a half and 10 and a half degrees Fahrenheit by the year 2100.

    US Okay. I have a great question here Dr. Nese, concerning other planets. Do other planets have weather or is having an atmosphere a prerequisite for weather?
    Nese You're right, that is a wonderful question. Having an atmosphere is a prerequisite for having weather; that is correct. So let's go through the planets and ask, which have an atmosphere. Venus. Thick atmosphere. Made of 90% carbon dioxide. Venus, therefore, has a huge greenhouse effect — it's 900 degrees on the surface of Venus. Mars has an atmosphere thinner than earth's but nonetheless has an atmosphere. Low-pressure systems and clouds have been observed in the Martian atmosphere. The most interesting weather in the solar system may be on Jupiter. Jupiter has a thick atmosphere but it's not made of the same things our atmosphere is made of. Jupiter's atmosphere is made of methane and ammonia, a very obnoxious atmosphere. But there are clearly storms in Jupiter's atmosphere. Huge, hurricanelike, swirling storms. The most famous of which has a name that the students may be familiar with. It's called "The Great Red Spot." So yes, other planets do have weather, but I don't think it's the kind of weather that you think of here on Earth.
    US No, no 900 degrees is beyond tanning weather I would think. I have a question here from Samuel who asks, "Do you know where the expression, "raining cats and dogs" comes from?"
    Nese Give me a minute.
    US Ok. We'll come back to it. If you remember, just let us know. I do have several questions about precipitation. First off before we get to that, is a halo around the moon, a sign of rain or snow?
    Nese That's another bit of folklore that has some truth to it. When sunlight or in the case of the moon, sunlight which bounces off the moon then comes to us, passes through thin ice clouds so-called cirrus of cirrus-stratus clouds and those clouds often appear in our skies, 24 hours or so before the arrival of a storm. So in some cases yes, a ring around the sun or moon, may tell you that snow or rain may be here in a day or so.
    US What is the difference between partly sunny or partly cloudy in a weather report?
    Nese According to the official National Weather Service definitions, there is no difference.
    US Okay.
    Nese However, having said that, the popular perception that I get from people is that there is a difference. But there isn't. In many ways it's forecaster preference. I tell you what I do, obviously you can't say--they both mean that the sky will be between say 30% and 70% covered with clouds or sunshine. So it's one of those in between forecast. You can never say partly sunny at night for obvious reasons. I know that sounds stupid but let me make that point. So what I do, I use partly sunny during the day and partly cloudy at night.
    US That makes good sense. I have a question, and I think it's a delicious one, just came in from Small Fry. Who writes, "Is it true that sometimes it rains fish or frogs?"
    Nese Well, sometimes is a perhaps a little strong. This has been observed, and it has been observed in situations where strong tornados suck up frogs or fish from a body of water. These animals get suspended in the air and then they fall some distance away from the body of water. Perhaps in a rainstorm. It has happened but it's not the kind of thing I'd be looking for the next time it rained.
    US Okay. What's a cloud?
    Nese Well, a cloud is a connection of millions and millions, billions and billions, of visible drops of water or crystals of ice.
    US And what are the different types of clouds?
    Nese Well, there's a couple of ways to categorize clouds. The most popular is to categorize them is how high they are in the sky. So you have clouds that tend to be low in the sky. Stratus clouds layer out and basically cover the whole sky. There are the puffy ones that look like cotton balls or pieces of cauliflower. Then you have mid-level clouds between seven and 20,000 feet. And then you have your high altitude clouds which are pretty much made of ice . So you can categorize them by the level at which they appear in the sky and then there are some clouds that are so tall that they take up all three levels. Your thunderstorms clouds are officially called cumulo-nimbus. "Cumulo" means "heaping", nimbus means, "rain." So a thunderstorm cloud is a heaping, rain cloud.
    US I would like to talk about snow some more.
    Nese I don't want to talk about snow.
    US I bet not. Why is snow light and fluffy while other times are heavy?
    Nese It's pretty much dependent on temperature.
    US Okay.
    Nese When the temperature is close to 32 degrees during the snowflakes' parachute to the ground you tend to get a little bit of melting. And snowflakes tend to stick together when wet. So when the temperature is 32 as it happened to be in Philadelphia much of the time on Monday, the snowflakes are big and the snow is wet. On the other hand, when the temperature is lower, 20-22 degrees none of that melting occurs, and the snow flakes are very light and the snow is much easier to shovel.
    US Speaking of parachuting to the ground, Baked Potato asks, "f you went sky diving through a cloud what would it feel like?"
    Nese Well I wouldn't do it through a Cirrius cloud but if you have parachuted through a cloud, I have not done this, but I have spent time in a cloud because I have been in fog. So imagine walking through a thick fog. I'm assuming this parachuting would take place from a high altitude so it would certainly be a lot colder than your walking through your October valley fog. But just imagine walking through a very thick or driving through a very thick fog. That's how it would feel parachuting through a cloud, but it would be a lot colder as I said.
    US I would like to step back for a second to the cats and dogs question. We got an email from Alberto that found a website that speaks to the origin. It says, "It seems that cats were at one time thought to have influence over storms, especially by sailors, and that dogs were symbols of storms, often accompanying images and descriptions of the Norse storm god Odin." The piece goes on to say that Jonathan Swift was the first to use the phrase in print. But for anyone who is interested in etymology, you can go to http://www.quinion.com/words/qa/qa-rai1.htmand you will find your fill on raining cats and dogs. Okay, back to snow. Dr. Nese, is it true that no snowflakes are alike?
    Nese Before I answer that, I would like to make one point about what you just said.
    US Sure.
    Nese I have found in many cases when investigating the origins of folklore that you can get different stories from different places. So I would encourage anybody who investigates that, to not accept ... I'm not saying that what you've just said is wrong, because frankly I don't know, I have never heard that. I do know that many of these folklores have several explanations. "Indian summer" is a good example. If you do a web search on "Indian summer" you'll find a half a dozen explanations for the origin of that term. Okay. So you're question about snowflakes ...
    US Wait wait wait before we get to the snowflakes. Tell us about Indian summer, where did that come from?
    Nese Well, obviously the origin has something to do with Native Americans. It's thought that Indian summer might be a time that Native Americans recognized sometimes occurs in the fall where they have extra time to gather harvests to store up for the summer. That's one potential explanation of where Indian summer originates. There are some who say, and this may not be the most completely politically correct, but this is what the research shows, that when the English men when they came to--when they came to America, they noticed this warm period that resembles summer but it comes later than regular summer. In the same spirit that we would call someone an "Indian giver," someone who gives and then takes back, you might call the period of extra warmth that comes during the fall, a period of summer that you give but then you take back. It's an Indian summer. Other explanations claim that the term was being used in Europe even before it was being used in the new world because there are European equivalents to Indian summer and they go by names ... uh I can't remember... Saint Martin's summer, perhaps, in England. It's just fascinating, when you research some of this folklore, to find that many of them we just don't know for sure. What was the original question?
    US Snowflakes.
    Nese Ah, snowflakes. Well, I have not checked every snowflake nor has any scientist. So we of course can't be positive that no two snowflakes are alike. But think of it this way, a snowflake's journey to the ground can be quite complicated and quite turbulent. That snowflake may have begun at 20,000 feet, in air with a temperature at 7 degrees below zero, with very limited moisture. There are invisible particles in the atmosphere called ice nuclei; these may be particles of clay that somehow become suspended in the atmosphere. Some of those particles, their structure resembles that of water vapor. So water condenses on to the particle and starts to grow, and runs into other crystals (unintelligible) and fractures and then it breaks, and on its way down it combines with other (unintelligible) and by the time it hits the ground, and all of that depends on the temperature and moisture content of the air on the way down, so after all that, the snowflake lands on the ground. And so I would like to think of as an analogy like human fingerprints. We know that fingerprints look similar, but when you look at it under a microscope they are not. Snowflakes are the same thing. They lead a complicated life, and by the time they arrive here, their past history precludes any two to be exactly alike at the microscopic level.
    US That's fascinating. I didn't realize that snowfall was such a violent event.
    Nese There is a couple of cool web sites, let me see how long this website is. Certainly you can get it, where there are some excellent snow images. I'll just read it to you, and then it could become part of the ... I may read it too fast to copy down http://www.its.caltech.edu/~atomic/snowcrystals/ and some fascinating research on snowflakes.
    US Dr. Nese, this big storm that we had last Monday, had really, really, large snowflakes. Now usually I've observed that in storms the really big snowflakes happen at the end. But here these were really large snowflakes throughout. What's up with that?
    Nese This goes back to a previous question; the size of the snowflakes is not a function of whether it occurs at the beginning or end of the storm. I'll come back to that. It's a function of the temperature structure of the atmosphere on the way down. And on Monday, as we talked about earlier, a large layer, a thick layer of the atmosphere, had a temperature very close to that critical 32 degrees. So that allowed a lot of melting to occur on the snowflakes and the more they melt the more they tend to stick together. You can think of the water as sort of like glue. In many storms though your observation is not incorrect. In many storms in this part of the country, it's at the end of the storm where you might tend to get enough warm air in so that the temperature does approach that critical 32-degree number. So it's not incorrect to say that you may have seen more of this happening at the end of the storm but it is not exclusively an end of storm characteristic.
    US Dr. Nese, I think we have a lot of Pennsylvanians with us today because there are a lot of questions about Punxsutawney Phil and the groundhog's weather predicting ability. Can you tell the rest of the country about Punxsutawney Phil, what he does, and how accurate his predictions are.
    Nese Well he is a groundhog; he doesn't know anything about the weather. I'm sure everybody realizes that and if they don't, I'm glad to have (unintelligible). It's a farce. I mean, it's a show. And it should be treated as such. You can go to the Punxsutawney Phil website and you can see what his predictions have been and you can compare it to what has actually happened and people have done that. It's just a joke. It's funny. It makes for good television, but has nothing to do with the weather.
    US There is an old phrase that goes, "It's not the heat it's the humidity." What does that mean?
    Nese I'm not exactly; there are several ways to interpret that. First of all 100-degree heat in Phoenix, Arizona, feels very different than 100-degree heat in Philadelphia, Pennsylvania. Because 100-degree heat in Phoenix, Arizona, is typically accompanied by very dry air. On the other hand if you get to 100 in Philadelphia, in many cases the humidity is excessive as well. And that puts more stress on the body. A 100-degree humid day in Philadelphia — which by the way is uncommon, temperatures do not get to 100 very often in Philadelphia — will feel much more stressful on the body than a 100- degree in Phoenix. I suspect that's what's being implied here. It's not necessarily the heat that does you in, but if the humidity is thrown in there as well, the body is stressed much more.
    US Dr. Nese, we have about 10 minutes left in our interview today. All schools participating please email, and get your questions in. I have question in California, Curious writes, "We're here in California. Why is it cool on the coast but so hot in Death Valley?"
    Nese Well along the coast of California, the weather is controlled by the Pacific Ocean. So any time air is coming in off the ocean, anytime you have a west wind, or southwest wind, or northwest wind, as the ocean goes, so goes the coast. Which means during the summer, it can't get very warm, and during the winter it doesn't get brutally cold. Inland, you don't have that influence anymore. Death Valley is located, it's very low elevation, in fact Death Valley is officially below sea level. Any time the winds come from the west, to get to Death Valley they have to come down from the mountains. When air sinks it warms. So Death Valley is located on the eastern side of some very high elevations and gets sinking or subsiding air, which is warming air.
    US Okay. We've had a few questions come in about lightning. First, I should ask what is lightning?
    Nese Well, lightning is an electrical discharge in the atmosphere that's akin or similar to static electricity that you might generate yourself. I like to tell kids that they have created lightning themselves if they've ever walked up to a car, another person, or a door knob touched it and got shocked. So lightening is just an electrical discharge in the atmosphere.
    US Ok. Can lightning strike twice on the same spot?
    Nese Absolutely. Many, many places, particularly higher elevations, have been struck numerous times. In fact, there is a neat statistic about the Empire State Building, and if you give me a second I can quote it, since I wrote it.
    US Sure.
    Nese The Empire State Building is struck by lightning on average 23 times per year. On one occasion the building was struck 8 times in 24 minutes. Lightning very much prefers high elevations, and so if you live in a higher elevation, or near tall objects such as electrical poles, flag poles, the probability of you being struck is higher.
    US I have a question that just came in from Bob in Atlanta who says, "My teacher told me not to be on the phone during a thunderstorm, can I talk on a cordless phone?"
    Nese Yes.
    US Okay. A follow-up, I've often heard that it's unsafe to be in a car during a lightening storm is that true or is that kind of more of those old wives tales?
    Nese Being inside a car is the second best place to be in a thunderstorm behind being inside a sturdy building. A car is safe, as long as it is not a convertible. The reason a car is not safe is not because of the tires. That's a myth. Because if lightning were to strike the car, the metal skin of the car would conduct the electricity into the ground where it would be safely dispersed. So if you're inside the car with the windows rolled up and you are not touching any metal inside a car and of course there is not much metal inside a car anyway, you should be safe.
    US Okay. I have a follow-up question from Myra, she asks, "Why do some flashes of lightning seem to go straight down to earth, whereas others go across the sky.
    Nese That's a neat question. It turns out that most lightning does not go from the cloud to the ground. Most lightning stays up in the atmosphere. It either stays inside a particular thunderstorm cloud, or it goes from one cloud to another, or in rare cases, it can go from the cloud to the air. Only 20% of all lightning strikes actually hit the ground.
    US Dr. Nese we only have a few minutes here. I'm going to ask you some rapid-fire questions that have come in throughout the day. Lula, asks, "Are there any places where the weather is pretty much constant and predictable?"
    Nese San Diego.
    US And why would that be?
    Nese Well, San Diego is far enough south that it's basically out of the main stormy belt. It's on the ocean, which moderates the climate. If you want to go international, go to the tropics, the weather never changes there.
    US Great. Is there any particularly safe place in the world to live weather-wise? Safe from hurricanes, monsoons tornados, etc?
    Nese San Diego. San Diego, really has a very stable climate. They don't get a lot of thunderstorms, they don't get a lot of hurricanes or a lot of rain. No place is completely immune to all kinds of weather changes. I can tell you that the mid-latitudes, the zone between 35 and 50 degrees north is probably the most active place in the world to live.
    US Dr. Nese, we have about two minutes left. Do you have any favorite weather stories that you would like to share with us?
    Nese Favorite weather stories? Well, I would rather answer questions.
    US That's fine. We still have plenty to ask you.
    Nese Let me give some thought that that, I wasn't prepared to give a weather story.
    US That's fine. What kind of advances do you expect in the ways of predicting weather in the future? What can we look forward to?
    Nese I think the biggest advance will come in our ability to measure the atmosphere from space. Most people are familiar with satellites; they know satellites can see where the clouds are. Guess what? We're learning how to measure other things from satellites: temperature, wind, and humidity. And once we master that, that will be a major breakthrough.
    US Thank you very much, Dr. Nese. This was fascinating. We all love talking about the weather. I would like to do it for another hour, but unfortunately we can't. I would like to thank the Franklin Institute too for what ever help they provided us. And one last question, real quickly. What's tomorrow's weather going to be? How should we dress here in Philadelphia?
    Nese You have record warmth tomorrow, high of 62, the record is 64. Rain tomorrow night.
    US Thank you for that sunny forecast. Thank you, Dr. Nese.
    Nese You're welcome.
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Meet the Historians

These renowned historians and experts chatted with students online. Read the transcripts.

Carol Berkin
Colonial Women
Ira Berlin
Joseph Ellis
Thomas Jefferson
James Loewen
Debunking History
Jon Nese
The weather
Robert Regan
Edgar Allan Poe
Robert Remini
The Jacksonian Era
Brooks Simpson
U.S. Grant and Reconstruction
David Traxel
Errol Uys
Riding the Rails
Cheryl Walker
Native American Lit
Mike Wilson
Jack London
Gordon Wood
American Revolution