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This will be one of our more crafty weather experiments, but it’s one that you will be able to use again and again. A barometer is an instrument we use to measure air pressure. At the bottom of this post, I’ll explain why air pressure is critical in forecasting the weather.
WHAT YOU NEED:
• Short, wide-mouth jar
• Plastic straw
• One sheet of cardstock
HERE'S HOW IT WORKS:
• When the air pressure is HIGH, it pushes down harder on the top of the balloon which makes the tip of the arrow go up.
• When the air pressure is LOW, the air inside the jar pushes up on the balloon harder than the air outside which makes the tip of the arrow go down.
• Check your barometer once a day and draw a line where the arrow is. Notice is it higher or lower than yesterday? Higher or lower than your baseline? Connect those observations to what the weather is doing. When you observe high pressure, what does the sky look like? When you observe low pressure, what is the weather doing? Use all of these observations together over the next days, weeks, and months to see how pressure dictates weather.
WHY PRESSURE IS IMPORTANT IN THE WEATHER:
Pressure is the whole ball game. Changing pressure changes how the wind is moving in the atmosphere. Think about rolling a ball down a hill. If the hill is really steep, the ball will roll much faster. If the hill is more shallow, the ball will roll more slowly. And if the ground is flat, the ball won’t move much at all. In that analogy, wind is the ball and the steepness of the hill is the pressure changes.
High pressure generally means clear sky because the air in the atmosphere is moving down. That’s a very stable air mass so it’s harder for clouds to form and rain to develop. Low pressure generally means more clouds, rain, storms, snow, etc. Low pressure means the air in the atmosphere is rising, which is unstable and leads to the development of those types of features.