reflect Amy got up early this morning. She was excited to wear her new summer clothes to school. She put on her new yellow shorts with the pink flowers. She pulled on the matching t-shirt. Slipping her feet into bright pink flip-flops, she ran to the door. As she flung open the door, she heard a crack of thunder. Drops of rain splashed on her toes. It was pouring outside! A cold breeze made her shiver. How could this happen? It was beautiful yesterday! What observations and comparisons can we make about day-to-day weather conditions? Poor Amy had to change out of her new clothes. She was happy to use her red umbrella, though. Amy did not see the clouds the night before. Otherwise, she might have expected rain this morning. The wind had also started to blow. That is another sign of changing weather. Weather can change from day to day or even hour to hour. The types of clothes you decide to wear depend on the weather outside. what do you think? Take a look at these photos. What types of clothes would you choose in each case? 63
look out! It is important to know what the weather might be like. Weather affects how we get to school. It may affect the machines workers use to build a house or clean a yard. During strong storms we stay inside to be safe. You cannot always tell the weather by looking outdoors or by studying a photo. It can be pouring rain yet feel hotter than before the rain started. You may go for a hike on a bright sunny day, only to walk right into a chilly wind. If our eyes can trick us, how else can we tell what the weather will be like? Scientists use tools to help figure out different weather conditions around the world. A scientist who studies weather is called a meteorologist. We can also use those same tools to help us figure out the weather in our area. What tools can we use to gather weather information? Temperature tells us how much energy something has. When something has a lot of energy, it usually feels hot. When something does not have a lot of energy, it usually feels cold. The tool to measure temperature is a thermometer. You can use a thermometer to measure the temperature outside. It looks like it s freezing in this photo. The thermometer tells us that s true. Water freezes below 32 F or 0 C. Can t we just look at a thermometer to predict the weather? No, weather is more complicated than that. Precipitation, wind, and air pressure also affect weather. Precipitation: The rain that made Amy wet is precipitation. So is the snow that people ski on. Precipitation is snow, hail, sleet, rain, or any kind of moisture that falls from the clouds. Wind: Air that moves from one area to another is called wind. Wind moves clouds around the planet. This causes weather to change. Air pressure: Air is made up of tiny gas particles. You cannot see these, though. Even though we can t see them, they add up and can press down on large areas like our city or state. This force is called air pressure. Knowing the air pressure can help us predict rain or snow. It can even tell us to watch out. for a hurricane or tornado 64
try now You can tell how much precipitation has fallen using a rain gauge. Make your own rain gauge. This way you can tell how much rain, hail, or snow falls at your home. 1. Collect these items: a 2-liter plastic bottle, a pair of scissors, modeling clay, two rubber bands, two paperclips, and a ruler. 2. Ask an adult to cut off the top of the bottle. Cut it about 3 inches down from the spout. 3. Press clay into the bottom of the bottle. This will make a flat base. 4. Place the spout end upside-down inside the other half of the container. 5. Attach the spout end to the other half of the container with two paperclips. 6. Place two rubber bands around the lower and upper parts of the bottle. 7. Slide a ruler underneath both rubber bands. The bands will hold the ruler in place. 8. Put the bottom of the ruler where the modeling clay starts. 9. Put the rain gauge in an open area outside. Make sure it is not close to trees or buildings. 10. Record the rainfall at the same time every day. 11. Empty the rain gauge. This rain gauge measures precipitation in inches and centimeters. How can we measure the air? A wind sock shows you wind speed and direction. The angle of the wind sock tells you the wind s speed. When it is not moving very much, there is little or no wind. A wind sock may also fly straight out, like in the photo below. That means high wind. If the wind sock is blowing to the north, the wind is coming from the south. If it blows to the east, the wind is coming from the west. A barometer is a tool that measures air pressure. When the air pressure falls, a low pressure system is moving into the area. These systems usually cause rain or other storms. If the air pressure rises, a high pressure system has arrived. The weather will likely be clear but colder. The top image is a wind sock. This wind sock is blowing in a strong wind. The bottom image is a barometer. The gold needle shows the normal air pressure for the time of day and year. The black needle shows the current air pressure. 65
Scientists in the Spotlight: Evangelista Torricelli Barometers are used every day to predict weather. Evangelista Torricelli invented this useful tool more than 300 years ago! Torricelli was an Italian scientist who taught math. He solved some of the hardest math problems of his time. Torricelli discovered the barometer while he was trying to solve another problem. Miners struggled with water pooling on the floor of the mines. Pump makers tried to pump out the water. However, they could raise the water only about 10 meters. They needed to raise the water higher to get rid of it. People thought it must a problem with the pumps. Torricelli thought it might be the pressure of the air pushing down on the water. He designed an experiment using the element mercury. (Mercury is much denser than water. He would have had to use a lot more water in his experiment to see a similar result.) Torricelli filled a tube with mercury. He turned the tube upside down, and placed it in a pool of mercury. He found that if the air pressure is high, the mercury level in the tube rises. Torricelli had discovered the barometer. His barometer proved that air pressure was causing the problem with the water pumps. How can we record weather information? Tools like thermometers help us know more about the weather outside. If we record measurements from different times or places, we can compare the results. This helps us predict what the weather will be like. Here are some tips for recording data about the weather. Use the same journal each time. Make your recordings at the same time of day. Also, use the same units of measure each time. For example, in the United States most people record temperatures in degrees Fahrenheit ( F). However, scientists usually record temperature in degrees Celsius ( C). Precipitation should be recorded in centimeters. 66
Graphs are a great way to compare your results. There are several kinds of graphs. Bar graphs show numbers as lines with different lengths. According to this bar graph, which month received the most rain during the past year in Houston? Line graphs show trends over time. According to this graph, when were temperatures in Houston the lowest during the past year? When were they the highest? 67
What Do You Know? Complete the following crossword puzzle using weather terms from the box below. Air pressure Precipitation Thermometer Wind sock Barometer Rain gauge Weather Meteorologist Temperature Wind Across 2. An instrument that measures the temperature outside 4. An instrument that measures air pressure 7. An instrument that measures the amount of precipitation 10. Rain, snow, hail, or sleet that falls from the clouds Down 1. A scientist who studies weather 3. How much energy something has 5. The state of the air outside, including its temperature, precipitation, wind, and air pressure 6. The force of air molecules pressing down on Earth 8. An instrument that measures wind direction and speed 9. Another word for moving air 68
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connecting with your child A Weather Routine To help students learn more about weather, make information collection part of their morning routine. Station a thermometer just outside one of the house windows and ask your child to record the temperature every morning. You can also hang a barometer on the wall and have your child record air pressure as well. It is possible to build every part of a home weather station as a fun weekend activity. Students can make homemade barometers, wind socks, weather vanes, and rain gauges. If they get in the habit of keeping a daily science journal and recording their data, students can easily use this information for later science fair projects or school assignments. Better yet, they will gain a hands-on understanding of local weather patterns. After they have collected data over several weeks, encourage students to place their information in colorful graphs and give a home weather report, just like television forecasters do. Ask them to make a 3-day forecast that is, a prediction of the weather over the next three days. Here are some questions to discuss with students: What conditions lead to sunny days? Rain and snow? How does your recorded information help you predict the weather? Why do meteorologists have trouble predicting the weather sometimes? 70