Ways to Predict a Storm With Air Pressure

Air pressure can change the color of the sky and give you a clue about upcoming weather.
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When you step outside and take a deep breath, you probably don't feel like the air around you has much substance to it. However, the air is made up of gases and actually has mass. In the atmosphere, cold air is denser and drier than warm air. When cold air encounters warm air, the warm air rises over the cold air and makes surface air pressure drop. As a result, a low pressure system forms and winds begin to blow. This is how storms form in response to changes in air temperature. By knowing how different elements react to air pressure, meteorologists can predict when a storm might occur.

Using a Barometer to Measure Air Pressure

A ​barometer​ is a tool that an individual can purchase or make to gauge air pressure and make basic weather predictions. When barometric pressure is stable, it is an indication of good weather. However, when the pressure quickly falls, it means a storm is on the way. If you have a barometer, you can use this to help you predict when a storm might roll in.

The measurements on a barometer are in millibars. Normal air pressure at sea level is about 1,013.25 millibars. When there’s a hurricane, the pressure can drop down to 30 millibars. Drops in pressure also help indicate the strength of winds in a storm, as greater drops yield stronger winds. These drops in air pressure might not be noticeable to humans, but some animals can feel pressure drop and take cover when storms approach.

Using Technology

Meteorologists also use other, more advanced equipment like weather balloons and highly sensitive barometers to measure air pressure and predict weather patterns. Weather balloons collect data starting from three meters off the ground, and transmit the data back to the ground for analysis. Weather balloons measure factors such as temperature, wind speed, humidity and atmospheric pressure in the troposphere and the stratosphere.

Meteorologists also use satellite images to look at clouds and radar to measure rain. They then enter the data gathered into a computer that has a forecasting program. The information that the forecasting program provides helps predict storms and other weather events.

Looking at the Morning Sky

The old saying, “Red sky at night, sailor’s delight. Red sky in morning, sailor’s warning,” may have some truth to it. Since winds blow from west to east in the Northern Hemisphere, storms generally come in from the west. The color of the sky comes from rays of sunlight that are scattered off water vapor and other particles in the atmosphere.

When the sun sets in the evening its rays scatter off the thickest part of the atmosphere. When the weather is going to be nice, you see the red wavelengths of color in the sky when the sun sets because the blue wavelengths get scattered and broken up in the atmosphere’s warm air. When the cold air replaces the warm air in the morning because of a passing storm, the sky will be a deep shade of red. A deep red color results from a high concentration of water in the atmosphere, indicating that the area will have rain and helping sailors predict poor weather.

Looking at the Moon

There’s also an old rhyme that says: “When there’s a ring around the moon, rain or snow is coming soon.” This large ring looks like a halo or dim rainbow around the moon. The halo effect occurs when the moon’s light ​diffracts​, or bends, off small ice crystals in the atmosphere. The ice crystals form thin clouds that you may or may not see. The high clouds occur because of a change in air pressure and generally indicate that storm clouds follow.

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