Air is made up of gases and 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. Storms form in response to changes in air temperature. By knowing how different elements react to air pressure, you can predict a storm.
Using a Barometer
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. The measurements on a barometer are in millibars. NASA shares that 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.
Meteorologists use equipment like weather balloons and barometers to measure air pressure. The Georgia Public Broadcasting site shares that these professionals 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,” has some truth to it, according to the Library of Congress. The government agency explains that, 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.
Looking at the Moon
There’s 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 Indiana Public Media website explains that 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.
- NASA: How Air Pressure Signals Changes in the Weather
- NASA: Feeling Pressured?
- Georgia Public Broadcasting: Talking Up a Storm
- Library of Congress: Is the Old Adage “Red Sky at Night, Sailor’s Delight. Red Sky in the Morning, Sailor’s Warning” true, or is it Just an Old Wives’ Tale?
- Indiana Public Media: A Ring around the Moon
- Comstock/Stockbyte/Getty Images