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A Meteorologist’s Best Friend

Have you ever seen a television weather caster show a colored map of where rain or snow is falling? The colors that you see indicate where the precipitation is and how heavy it is. So, how does he/she get this information? The precipitation is detected by one or more of the National Weather Service’s 150 weather radars, processed by computers and made available to weathermen around the world. So, what is radar and how does it work? RADAR is an acronym for RAdio Detection And Ranging and was developed more than 100 years ago when countries around the world realized radio waves could be used to detect objects that the human eye couldn’t see. Now, weather radars are used to help meteorologists see raindrops, snowflakes, hail and other small objects in the atmosphere. Weather radars send out a burst of radio waves from a large dish inside the radar dome. The radar dome looks like a large ball on top of a tower. The radio waves travel through the air until they hit something in the atmosphere. When they hit an object, some of the radio waves bounce off the object and travel back toward the radar. The radar listens for these reflected radio waves, something that is called a radar “echo.” From the echo, the radar figures out how much energy (radio waves) is returned to the radar, as well as how long it took to return. Using this information, the radar estimates how heavy the precipitation is and how far away it is. As the radar’s dish spins around inside the dome, it sends out hundreds of bursts of energy each second and collects information on the reflected energy. One full scan of the atmosphere takes around five minutes to complete. Weather radars also employ Doppler technology (that’s why weather radars are often called Doppler radars). Doppler technology allows the radar to determine whether the individual rain droplets or snowflakes are moving toward or away from the radar, which then allows the radar to estimate the winds in a storm. Meteorologists use this wind information to help warn people of gusty winds from a thunderstorm or to detect rotation in the atmosphere that could lead to the formation of a tornado. Ideally, the weather radars would detect only rain, snow or other precipitation, but objects like birds, insects and even passing traffic on a nearby highway can reflect energy back to the radar. Fortunately, recent improvements to weather radars now allow meteorologists to better understand what the radar is seeing. Meteorologists can determine whether the precipitation is rain, snow, sleet or hail. By knowing the type of precipitation and how heavy it is, the radar can also make estimates of how much rain or snow has fallen. Radar is truly one of the most valuable tools a meteorologist can use. In the summer, it is the best tool for watching for developing thunderstorms, tornadoes, strong winds and heavy rain and is used to issue warnings for dangerous storms. In the winter, the radar can be used to monitor winter storms and see snow, sleet and rain.

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Kids

Satellites

A Weather Forecaster’s Eye in the Sky By John Jensenius Weather systems are constantly moving around the globe. Storms develop, intensify and eventually dissipate as they move from one area to another. While these storms are over land, meteorologists rely on a variety of weather observations. However, while over the oceans, meteorologists rely on satellites to observe these weather systems. In particular, satellites are extremely important for tracking tropical storms and hurricanes as they develop and move across the ocean. There are two main types of weather satellites: polar-orbiting and geosynchronous. The polar-orbiting satellites orbit around the north and south poles as the earth rotates underneath their orbit. Each pass of the polar-orbiting satellite can be stitched together to form a complete picture of the weather around the globe. The second type of satellite is the geosynchronous (sometimes called geostationary). These satellites orbit the globe around the equator and revolve around the earth at the same speed as the earth rotates. Because these satellites move at the same speed as the earth’s rotation, we say that their orbit is synchronous with the earth. This synchronous movement allows them to appear as if they are stationary — that is, they always stay over the same location on the earth. To maintain a synchronous orbit, they remain above the equator at an altitude of about 23,000 miles. Weather satellites are equipped with a variety of sensors that measure different weather variables. One sensor measures the amount of sunlight reflected back to space by objects on the ground and in the atmosphere. This data creates a visible satellite picture. Clouds show up white on the visible image because they reflect much of the sun’s light. Like clouds, snow on the ground also shows up very light. In contrast, the oceans, which absorb most of the sunlight, appear dark on the visible image, as do heavily forested areas. One of the limitations of the visible image, is that it can only be used during the sunlit hours. At night, the visible image is dark. Another type of sensor is the infrared sensor. This sensor measures the temperatures of the objects it sees. Although temperatures can be shaded any color, on most black-and-white images, the warmer objects are colored darker while the colder objects are lighter. For example, warm tropical waters and hot land areas appear dark, whereas clouds, especially high clouds in the atmosphere where temperatures are very cold, appear white. On sunny days, you can watch land areas on the infrared image turn darker as the sun heats them. One advantage of the infrared sensors is that they can produce images both day and night since objects always have a temperature. Other sensors onboard weather satellites provide meteorologists with information on moisture in the air, the temperature structure of the atmosphere, whether fog is forming and a variety of other information about the atmosphere. In the next few years, satellites will start providing information on lightning flashes across the United States. So, whether it’s day or night, weather satellites are keeping an eye on the weather.

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Kids

Hurricane

By Richard Henning Have you ever wondered how television broadcasters know how powerful a hurricane is? Although meteorologists at the National Hurricane Center (NHC) in Miami, Florida, have many tools to help predict these storms, the best way to determine the strength of a storm is to fly into the hurricane and measure the winds directly. The National Oceanic and Atmospheric Administration (NOAA) operates a fleet of aircraft from their base in Tampa, Florida. These aircraft fly a variety of research missions during the year to study the Earth’s oceans and atmosphere. Two of these planes (WP-3D Orions) are designed to fly directly into hurricanes while a third plane (Gulfstream G-IV) is used to collect data from around the storm. The two WP-3D Orions are large, four engine turboprop planes that are similar to the P-3 patrol aircraft that have been flown by the U.S, Navy for the last 50 years. Both Orions have been flying since 1976 and are known by their Muppet nicknames, Kermit (tail number N42RF) and Miss Piggy (tail number N43RF). They fly through the eyewalls of hurricanes, where the strongest winds are found, at altitudes ranging anywhere from 1,500 feet to 12,000 feet above the ocean. The men and women who fly into the storms are called the NOAA Hurricane Hunters. Typically, a crew of up to 18 people is onboard the plane. This group includes meteorologists, pilots, a navigator, engineers and technicians that operate all of the scientific equipment. The meteorologists onboard the aircraft direct the pilots as they fly through the eyewall and into the eye of the storm. While flying through the eyewall, the crew releases a special instrument called a dropsonde, which falls by parachute and measures the wind speed just above the ocean surface before it splashes into the water. The dropsonde has a GPS sensor that tracks the dropsonde’s location and a radio transmitter to send information back to meteorologists on the plane. The meteorologists then pass this information via satellite to the National Hurricane Center where it is sent via the Internet to broadcasters around the country. Once Kermit or Miss Piggy reaches the eye of a hurricane, the crew releases another dropsonde to measure air pressure. Meteorologists use these air pressure measurements to help determine the strength of the hurricane, whether a storm is getting stronger or weaker and how quickly the pressure is changing. The Gulfstream G-IV, nicknamed Gonzo, flies at up to 45,000 feet to collect data from the top portions of the hurricane. This jet is operated by a crew of up to 10 people. The crew sometimes releases more than 30 dropsondes on a single flight to measure the environment around the hurricane to help forecasters determine where the storm will go. So, what is it like to fly into a hurricane? Since the eyewall of a hurricane has very strong winds that go up, down and in different directions, it’s a wild ride full of turbulence and makes the flight seem a lot like a roller coaster. But the Hurricane Hunters know that the data they collect will help forecasters better predict the path of these potentially devastating storms and protect the lives of others. Richard Henning is a Meteorologist and the Flight Director at NOAA’s Aircraft Operations Center.

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Kids

Have a Great Summer and Beat the Heat

By Jannie Ferrell, Meteorologist, National Weather Service Summer is a favorite season for many of us. It’s fun to spend time with our friends and family swimming, camping, playing sports, hiking and picnicking. Some days can get very, very hot. In fact, extreme heat can be dangerous and make people very sick. During the summer, a heat wave may occur. This happens when it is hotter than normal over several days, generally when the temperature outside is 10 degrees Fahrenheit or more above average. When the heat is combined with very high humidity, it is even more dangerous. Unlike other weather hazards such as thunderstorms, tornadoes and hurricanes, you can’t see a heat wave coming, but you can feel the effects of it. Fortunately, the National Weather Service alerts us when extreme heat is coming. Weather forecasters use a temperature measurement called the Heat Index to help determine when to expect very hot and dangerous conditions. The Heat Index describes how hot it really feels by combining a measurement of air temperature and humidity. The most dangerous heat is when the humidity is high. Why? Because, it’s more difficult for sweat to help you cool down when the humidity is high. It’s very dangerous for your body to stay too hot for too long. So it’s important that you take precautions to prevent heat illness. The most severe heat illness is a heat or sunstroke and is a life-threatening emergency. Those most at risk for heat stroke are the elderly and small children. You’ve probably heard your local television weathercaster reporting on heat during the summer. Let’s say the weathercaster reports that the Heat Index is 110 degrees outside. Looking at the Heat Index scale, you see that’s in the orange and danger zone. Under that condition, you should not stay outside too long before taking a break in a cool place. You can stay safe and cool while you are having fun this summer if you follow these tips: • Stay indoors as much as possible. • Spend more time in air-conditioned places or places with fans. • Drink plenty of water. • Wear light-colored, lightweight and loose-fitting clothes, a hat, sunglasses and sunscreen. • When playing outside, take frequent breaks in the shade. • Limit your time in the sun, especially during the middle of the day when the sun is strongest. • Watch for symptoms of heat illness (cramping, rapid pulse, heavy sweating, dizziness, confusion, nausea, vomiting) and seek help immediately if these occur. • Listen to the radio and television, or check online (weather.gov) for the latest weather information and instructions for your area. So, make this the best summer ever! Play ball, take a hike, go to the zoo, spend time at the pool or have a cookout; just check the forecast and stay safe to beat the heat! Learn more about heat safety at www.weather.gov/heatsafety

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Kids

Beach Days

You’re at the beach for a day of fun and sun with your family. The water looks inviting — almost begging you to jump in and play. You wonder, is it safe to go in? Before you get in that water, make sure you pay attention to the water’s conditions and “know before you go.” Before entering the water along a beach, know the conditions of the water. The water may look safe, but there can be many dangers. If there are breaking waves (surf) along a beach, the water washing up on the beach often returns to the ocean in the form of a rip current. Rip currents are narrow channels of water that move away from the shore at a faster speed than the water surrounding it. They are strongest just below the surface. Rip currents can sweep even excellent swimmers out to sea, sometimes causing them to panic and drown. Learn about rip current safety at www.ripcurrents.noaa.gov/. Here are some good ways to “know before you go” and make yourself aware of the water conditions: Talk to a Lifeguard or Beach Patrol. No one knows the current water conditions better than lifeguards or beach patrol. They are trained to detect dangerous currents and waves and know other conditions such as the water temperature. Know What the Warning Flags Mean. Beach warning flags are often posted on or near a lifeguard’s stand. Typically, a green flag means water conditions are safe, but other colors usually mean conditions are not safe. Check the Surf Zone or Weather Forecast. Surf Zone Forecasts from the National Weather Service can be found at www.nws.noaa.gov/beachhazards/surfzones.shtml. Click on the dot closest to the beach you are visiting. You can also ask the hotel or rental agency where your family is staying for local sources of weather and beach forecasts. Inspect the Water Yourself. Beaches are more dangerous when the waves are larger and there is less time between breaking waves. One clue that there might be a rip current is when the water in an area looks different than the surrounding water. If you see an area that appears dirtier than the nearby water, or if you see an area where the water is moving away from shore while the surrounding water is moving toward the shore, you’re likely seeing a rip current. Rip currents and other dangerous currents are also more likely near structures and jetties. So, know before you go and you’ll be safe from head to toe! Wayne Presnell is a meteorologist with the Marine and Coastal Services Branch, National Weather Service, NOAA. Please visit the National Weather Service’s (NWS) Beach Hazards and Safety website to learn more about beach hazards and how to stay safe at the beach: www.nws.noaa.gov/beachhazards/.

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Kids

Fascinating Facts about Lightning

You may have heard that lightning never strikes the same place twice. Well, that’s not true. Many of the tall buildings in the world are struck multiple times each year by lightning. In this article, I’m going to separate the facts from the myths and answer some of the frequently asked questions about lightning. Do the rubber tires on a car protect you from lightning? No, the rubber tires on a car, bike or other vehicle won’t protect you from lightning. What will protect you is the outer metal shell of a hard-topped metal vehicle (no convertibles). Cars are struck by lightning every year. Usually, the lightning damages the electronics in the car and blows out a tire or two, but the people inside are safe (but often a bit scared by the incident). How hot is lightning? Lightning is electricity. As electricity passes through something it causes heat. When lightning passes through the air, it can heat the air to as much as 50,000 degrees Fahrenheit — five times hotter than the surface of the sun. When lightning strikes a home, it can create enough heat to ignite a fire. How powerful is lightning? There’s enough electricity in a flash of lightning to power a light bulb for about a year. However, because a lightning flash happens in a small fraction of a second, all that power is discharged in a small amount of time and causes a very bright flash. Does the lightning go from the cloud to the ground or from the ground to the cloud? The answer is that lightning goes both ways. In the most common lightning flash, negative charges move from the cloud to the ground as a bright flash moves from the ground to the cloud. How fast is lightning? The stepped leader which precedes the flash moves downward at 300,000 mph. The bright flash moves upward at 300,000,000 mph — now that’s fast! Do planes get struck by lightning? Yes, on average each commercial jet is struck once a year. Commercial planes are designed to withstand a lightning strike. If struck, the lightning passes through the outer shell of the plane. Does metal attract lightning? No, this is a common myth. However, if struck, metal wires and poles will conduct the lightning discharge. If a pond or lake is struck by lightning, will all the fish die? No, most of the electricity spreads out along the water’s surface. As long as the fish are not near the surface of the water, they won’t be harmed by the lightning strike. John Jensenius NOAA Lightning Safety Specialist

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Weather

Watch Out! Flooding Ahead!

You’re riding in a car, and the road ahead of you is covered with water — what should the driver do? You’ve crossed a stream to find that spot for the perfect picnic, but now that you’re ready to head home, the stream is deeper and the water is flowing faster than it was before — what should you do? The answer to these questions is “Turn Around, Don’t Drown.” Whether you’re in a car or on foot, never try to cross a flooded area or walk through swiftly moving water. Did you know that flooding can occur anywhere in the United States during any time of the year? The most common cause of flooding is rain. Sometimes floods are caused by summertime thunderstorms that produce a lot of rain in a short period of time. Other times, persistent rain and/or melting snow over several days can lead to flooding because the ground can’t absorb all of the water. Once the soil has become saturated, the rest of the rainwater will run off and into creeks, streams and eventually rivers. If the creeks, streams and rivers can’t hold all the runoff, the excess water not only floods these waterways, but also runs across roads, low-lying areas and sometimes backyards. If you’re outside, remember that it can take less than six inches of swiftly moving water to knock you off your feet. Even though six inches of water may not seem that deep, if you fall down, it will be nearly impossible to stand up again. Just a few inches of water can cause a car to stall and strand the passengers, possibly in the middle of a moving stream of water. While a few inches of water may not be able to move the car, it’s enough to make it dangerous for the people inside the car to get out and try to get to dry land. Instead of getting out of the car, call for help! Water may look fun to play in, but swiftly moving water is very dangerous. Whenever you see heavy rain, remember that rivers and streams can rise rapidly, and that dangerous streams can form in normally dry areas. Stay away from any rapidly moving water. You can keep yourself and your friends and family safe by reminding them to “Turn Around, Don’t Drown!” whenever you’re near a flooded area or swiftly moving water. To keep everyone safe, the National Weather Service issues Flood Watches and Warnings to alert people to flooding. A Watch means that there is a possibility of flooding in your area; a Warning means that flooding is occurring or is about to occur. If you hear a Flood Watch or Flood Warning, be aware of the flood dangers, and make sure that you are in a safe location. More information on these hazards and on flood safety is available on the National Weather Service Flood Safety website (www.floodsafety.noaa.gov).

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