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.
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.
- National Aeronautics and Space Administration: Air Has Weight and Temperature Affects it?
- National Aeronautics and Space Administration: Air Pressure
- Georgia Public Broadcasting: How Do Meteorologists Predict the Weather?
- Library of Congress: Is the Old Adage “Red Sky at Night, Sailor’s Delight. Red Sky in Morning, Sailor’s Warning” True, Or is it Just an Old Wives’ Tale?
- Indiana Public Media: A Ring Around the Moon
About the Author
Flora Richards-Gustafson has been writing professionally since 2003. She creates copy for websites, marketing materials and printed publications. Richards-Gustafson specializes in SEO and writing about small-business strategies, health and beauty, interior design, emergency preparedness and education. Richards-Gustafson received a Bachelor of Arts from George Fox University in 2003 and was recognized by Cambridge's "Who's Who" in 2009 as a leading woman entrepreneur.