Backyard

Introduction/Motivation:

People have been forecasting the weather for thousands of years. Even you forecast the weather when you look out the window or step outside in the morning before deciding what to wear. In this case, you are using your senses to forecast the weather. You might be looking at the shape and color of the clouds in the sky, feeling how warm or cool the air is, or watching the trees to see if they are swaying in the breeze.

Modern is more complicated than using our senses to predict the weather—it really depends on the work of engineers and scientists. What are some of the engineering devices that are used today to forecast the weather? (Possible answers: Weather balloons, satellites, Doppler radars, computer programs, etc.) So, if engineers design this equipment, who uses it? Meteorologists and climatologists use these engineering devices to make weather forecasts. Everybody who plans a picnic, a camping trip, or flies an airplane depends on these weather forecasts. For example, pilots need accurate weather forecasts to make air travel safe and comfortable for passengers. Certain types of weather conditions, such as extremely high and severe thunderstorms can make air travel unsafe. You might also need to know the weather if you are planning a camping trip—the wilderness is beautiful, but it can be dangerous to be far from shelter during a storm.

Now let's try to imagine how people predicted the weather before engineers and scientists developed modern forecasting equipment (as shown in Figure 2). How do you predict the weather? For example, when you see a clear blue sky on a warm day, what do you expect to happen? Probably not much—your experience of this weather pattern has taught you that clear blue skies on warm days mean fair weather. What if you looked up at the sky and saw a gray cloud, hanging low in the sky? You know from experience that dark gray clouds usually bring rain or snow. In both cases, you are relying on the observation of known patterns to predict the weather. Observing weather patterns over time to predict the future state of the weather is how people forecasted the weather for thousands of years before engineers and scientists developed modern weather forecasting equipment.

TASK: Today, you will act as if you are an engineer! You will use your senses to observe weather patterns and then design forecasting equipment to make a weather forecast. As a state park engineer, it is your job to build a backyard weather station and make a weather forecast to determine whether or not Memorial Day weekend (May 23-25) will be safe and pleasant for camping. In order to do this, your backyard weather station needs to be up and running by Monday, May 18th so you can collect a least 5 days of data. Let's get started!

YOU WILL BE CREATING THE FOLLOWING:

Tool #1: Vane

Knowing the wind direction can help us understand weather patterns. What causes the wind to blow? Wind is created when air moves from an area of high pressure to one of low pressure. The greater the difference between the areas, the stronger the wind currents. Because the equator is constantly hot and the poles are cold, a general pattern to the Earth's air circulation exists. In many areas, the wind usually blows from the same direction. To forecast using a wind vane—or a weather vane—a device that shows from which direction the wind is blowing, is very simple, but it only works if the wind is strong enough (that is, a light breeze will not help much). The first step to using the wind in order to forecast is to determine the direction from which the wind is blowing. Generally, in the northern hemisphere, if the wind is from the south, it means that warmer weather is on its way soon. If the wind is blowing from the north, it means cooler and drier weather is coming. East- or west-moving winds can mean a variety of weather conditions, which makes it difficult to forecast using them. Also, basic wind forecasting rules do not apply if a large body of water is nearby. Wind that travels across a body of water feels cooler in the summer and warmer in the winter.

Tool #2:

We use a barometer to measure air pressure. Air pressure is the force exerted by molecules zooming around the Earth's atmosphere, constantly bouncing off each other and bumping into everything else. The faster these air molecules are zooming around and bumping into things, the greater the air pressure. We just learned that when molecules in the air speed up, the temperature increases. It follows, then, that when the air temperature increases, so does the air pressure.

If our barometer indicates that the air pressure is high, we can expect fair weather. High air pressure acts as a barrier to approaching weather systems, diverting their course. On the other hand, if our barometer indicates low air pressure, we can expect stormy weather. Low atmospheric pressure represents the "path of least resistance" for encroaching weather systems.

As a rule of thumb, if our barometer is falling, then stormy weather or some form of precipitation will occur, and if our barometer is rising, we expect nice weather or no precipitation (see Figures 6 and 7).

This barometer shows a falling pressure, indicating the arrival of stormy weather. This barometer shows a rising pressure, indicating the arrival of fair weather.

Tool #3:

A thermometer is an instrument that is used to measure temperature. We think of temperature as how hot or cold something is. But what is it really? The temperature of the air is determined by how fast the molecules in the air are moving around. When air molecules speed up, the temperature increases. So, how does observing the temperature help us forecast the weather?

First, we must look at climatology data to determine the average daily temperature in our area. Data is often collected over a period of about 30 years (see References section for links to climatology data across the US). So, once we have determined the average temperature in our area, we can make predictions about the weather using our thermometer. High temperature causes air pressure to rise, which indicates fair weather. Cooler temperatures cause the air pressure to drop, which can bring stormy weather.

Tool #4:

A rain gauge is a device that enables us to gather and measure the amount of liquid precipitation over a set period of time. Most rain gauges measure precipitation in millimeters; however, the level of rainfall is usually reported as inches or centimeters. Many different types of rain gauges exist, including graduated cylinders, weighing gauges, tipping bucket gauges and gauges that are simply buried in the ground.

By measuring the amount of precipitation, rain gauges help us understand weather patterns in localized areas. These instruments also help us determine the presence or onset of a weather front.