The Basics	In-Depth	Experiments	Witness Account
Words to Know	Experts Say	Be Ready!

Experts Say

Want to hear more about storms? Check out the transcript of a message board discussion with Weather Expert, Ingrid Amberger.

Dr. Jeffrey Masters, Director of Meteorology for the Weather Underground Web site, answered student weather and winter storm questions in the winter of 2001.

Dr. Masters received his B.S. and M.S. degrees in Meteorology from the University of Michigan. He has taught weather forecasting at the State University of New York at Brockport, and joined the Hurricane Hunters as a flight meteorologist for the National Oceanic and Atmospheric Administration's (NOAA) Aircraft Operations Center. You can see him in the 1988 PBS documentary NOVA show "Hurricane!" flying into Hurricane Gilbert.

Q: My friend and I are doing a science fair project, and we would like to know which town would receive more snow — a town in the valley or a town near a mountain?
A: Most likely, a town near a mountain. Mountains act as giant rain catchers — precipitation is almost always higher on a mountain compared with surrounding valleys. This is because when air hits a mountain, the air is forced upwards. Upward-moving air cools, and if this cooling is great enough, the air will cool to the point where it cannot hold any more water vapor. This water vapor then condenses, and falls as rain or snow.

Q: How do air masses differ from each other?
A: It depends upon where they start. An air mass that sits a long time over a hot, wet ocean will become hot and wet. An air mass that sits a long time over a cold, dry place will become cold and dry.

Q: In which direction does weather move: north/south or west/east? How come?
A: Weather can move in any direction. In the United States, weather most often moves west to east, because that is the direction the jet stream blows. The jet stream carries weather systems along with it. Now, you may ask, why does the jet stream blow west to east? The answer is complicated, but it happens as a result of the way the sun heats the equator more than the poles, and the speed with which the earth spins.

Q: How do you know that all the snowflakes have their own pattern?
A: There has been a lot of research done on the subject by many scientists. Scientists capture snowflakes and photograph them to study their patterns.

Q: Is it going to snow a lot this year?
A: If I knew the answer to that question, I'd be rich! Long-range forecasting of winter snow is more luck than science right now.

Q: Do you believe there are volcanoes under the ocean water, off the coast of Peru, that affect El Niño?
A: I don't think so — I don't think volcanoes are big enough to compete with the forces of the global winds which cause the El Niño.

Q: What exactly is sleet?
A: Sleet happens when the air temperature is above freezing near the clouds, where the rain is formed, and below freezing near the surface of the earth. As the rain drops, they fall through the thick layer of below-freezing air, and the raindrops freeze before they hit the ground. These frozen raindrops are called sleet.

Q: What is the difference between dew point and humidity?
A: The dew point is the temperature the air must reach in order to achieve 100 percent relative humidity — the point where the water vapor in the air starts condensing and clouds form.

Q: What's the hottest place that it has ever snowed?
A: The farthest south is has ever snowed in the continental United States is Miami Beach, Florida, in 1977.

Q: Why is Oregon so wet?
A: Oregon is so wet because the winds usually blow from west to east over the state. On the west side of the state, along the Pacific coast, the air is very moist. The air currents take this moist air and move it into the mountains, which run the entire length of the state. When moist air hits a mountain, the air is forced upwards. Upward-moving air cools, and if this cooling is great enough, the air will cool to the point where it cannot hold any more water vapor. This water vapor then condenses, and falls as rain or snow.

Q: What tools do you use to predict weather?
A: Weather data is gathered by weather instruments at over 10,000 airports worldwide, from weather balloons launched twice daily from about 1,000 locations around the world, and from weather satellites orbiting the earth. The first task in making a forecast is to look at these current measurements of the atmosphere and understand what the weather is doing now. It also helps to watch some time-lapse weather animations to see what has been happening over the past day or so, and make some estimates of how these trends will carry over into the future. Finally, we review the forecast made by supercomputers, and base our forecasts on those predictions — basing the final forecast on our analysis of the current weather, on weather trends, and our past experience.

Q: How can you predict if there will be a tornado?
A: Tornadoes always form inside severe thunderstorms. Usually, a large area of clouds inside of the thunderstorm will start to spin about 30 minutes before a tornado appears. So, once we see this spin start to develop, a tornado warning can be issued. However, not all spinning thunderstorms make tornadoes, so there are a lot of false warnings issued.

More information about tornadoes can be found in the Tornadoes section of Weather Watch.

Q: Please explain lake effect. I live in Michigan.
A: Any lake, if it is large enough, will change the weather around it. The effect is most noticeable in America around the Great Lakes area in winter. Cold air blowing across the lakes picks up large amounts of moisture as it passes over the relatively warm water beneath. When these moisture-laden winds hit the shore, they drop the moisture as "lake-effect" snows that are frequently very heavy — up to three inches per hour!

Q: When you chased hurricanes, how many would you say you chased? What was it like?
A: I chased six hurricanes, and about six weaker tropical storms and tropical depressions. You can read my account of my flight into Hurricane Hugo.

Q: What is the difference when a weather reporter says "partly cloudy" or "partly sunny"?
A: There is no difference. It's the weather reporters way of saying the glass is half-empty or half-full.

Q: Why does thunder make noise?
A: Thunder is the sound of air rushing in to fill a partial vacuum created when lightning passes through the air.

Q: Why is the snow white?
A: Snowflakes have a very complicated shape with lots of reflecting surfaces. When the white light of the sun hits a snowflake, so much of the light gets reflected back that we see the full white light of the sun scattered back to our eyes.

Q: What is the average amount of rain Hawaii gets every year?
A: Well, it depends on where you are in Hawaii. Honolulu, which is shielded by tall mountains from the moist northeast trade winds blowing off the ocean, gets only 22 inches of rain per year. But Hilo, on the northeast side of the Big Island of Hawaii, has no protecting mountains, and gets 130 inches per year.

Q: Which country gets the most rain every year?
A: Some mountainous areas of India receive over 400 inches of rain per year, primarily during their monsoon season.

Q: Why does it get more humid in some places than others?
A: You need three things to get high humidities:

1) You need to be close to a major body of water (preferably a warm one, like the Gulf of Mexico).

2) The wind must blow from that large body of water towards you.

3) There cannot be a range of mountains between you and the body of water, or else the mountains will intercept much of the moisture.

Q: Why is there water vapor inside clouds? How did it get there in the first place?
A: Water vapor's original source is from evaporation from the oceans, lakes, streams, or any other bodies of water. The sun's heat creates updrafts that lift the water vapor high in the atmosphere, where it is cold enough to condense the water vapor into cloud drops.

Q: What are the most important things you need to do to be prepared for a hurricane?
A: 1) Be ready to evacuate if the order comes.

2) Secure loose objects around your home; board up (DON'T TAPE) your windows.

3) Make sure you have a weather radio, flashlights, fresh water, plenty of food, and gas for your car, etc.

For more information about emergency preparedness, visit FEMA's Ready site for kids. FEMA stands for Federal Emergency Management Agency. It is the federal agency responsible for helping people before and after disasters.

Q: How does wind start?
A: Wind always starts because two areas have different pressures or densities of air. The wind will always blow to try to equalize these differences, so the wind blows from high to low pressure.

Q: Why did you want to be a weather person?
A: Well, growing up in the Midwest with its amazing variety of weather always made me want to learn more about it.

Q: What is meant by Indian summer?
A: Sometimes during mid or late fall, a period of unseasonable warm weather occurs with clear skies, sunny but hazy days, and cool nights. Indian summer doesn't happen every year, and sometimes happens more than once in the same year.

Q: How long can a blizzard last?
A: Blizzards usually last only a day in one location, since the jet stream usually moves them along pretty quickly. Sometimes, though, you get a "cut-off low," which is a storm system that is cut off from the jet stream. These cut-off lows can create blizzards (particularly in mountainous regions) that can last as long as a week.

Q: What is the hottest temperature it has ever been in history?
A: On September 13, 1922, at El Azizia, Libya, the recorded temperature was 136° F (58° C).

Q: Is global warming a threat to the Midwest?
A: Global warming is a threat to every region in the world, since climate change will occur everywhere. In the short term, it will seem like any change to the current climate in a region will be costly, since humans will be forced to adapt to whatever the new climate is. However, it is possible that global warming in the Midwest might be beneficial in the long run. It could increase the amount of rainfall along with the hotter temperatures. These conditions would mean a longer growing season, and that would mean increased crop yields for the farmers in the area.

Q: What does it mean that the ozone layer is being destroyed?
A: Human-created chemicals called chlorofluorocarbons (CFCs) have drifted up into the stratosphere, where they are attacking and destroying the protective layer of ozone. Destruction of the ozone layer lets more ultraviolet rays reach the earth's surface. This is dangerous to life on earth since overexposure to harmful ultraviolet rays can cause sunburn in humans and lead to many other problems for plant and animal life.

Q: What is hail made out of?
A: Ice. A hailstone starts off as a small chunk of ice. Winds blow the ice through parts of the thunderstorm where the cloud water is supercooled. What is special about supercooled cloud water is that it exists as a liquid even though the temperature is below freezing. As the hailstone travels through the supercooled water drops, the liquid water freezes onto it, making the hailstone grow larger.

1 2