Take a pressure reading with a barometer, record it on a weather website, or look for a weather map that depicts areas of high and low pressure. Find the precise pressure reading in millibars if feasible. Millibars are units of measurement for the weight of the atmosphere at a certain point. One millibar is equivalent to one thousandth of a pound per square inch (psi).
Weather maps can be very helpful in identifying areas of high and low pressure. These areas are called weather fronts. When a front passes through, it causes temperature changes because cold air is heavier than warm air. This creates a difference in pressure that pushes clouds away from the front and pulls clouds together ahead of it.
The pressure gradient caused by a front can be strong enough to cause storms or tornadoes. Knowing this, farmers protect their crops by moving them off the field when a frontal system approaches. This is called "safening" your crop.
High pressure systems are known for spreading disease-causing particles far and wide; therefore, they have a protective effect on people too. People living in areas where high pressure dominates the weather experience less severe weather than those who live in areas where low pressure dominates. High pressure helps prevent floods by holding moisture over land surfaces.
Low pressure systems are known for their destructive power; they can bring about sudden death by causing floods, damaging winds, and triggering earthquakes.
The National Weather Service collects atmospheric pressure data at various places around the United States using a ground-based sensor known as a barometer. These measurements are shown on weather maps by a blue "H" for high pressure and a red "L" for low pressure. Areas of high pressure tend to produce more stable air conditions than areas of low pressure.
In addition to the H and L symbols, other codes are used to indicate different levels of wind speed. A "G" stands for calm winds under 10 miles per hour while a "K" indicates 10-19 miles per hour winds are present. Widespread 20-29 mile per hour winds are indicated by an "I" and 30-39 mile per hour winds by an "M". Strong gale-force winds up to 60 miles per hour or more are labeled with an "R".
These codes are used in combination with the pressure value. For example, if the reading is 1015 millibars (mb) and there's no warning of precipitation, an "S" would be used to denote clear skies with high clouds at 1015 mb. If there was a warning of precipitation, an "W" might be used instead.
Winds of this strength are not common in most parts of the country, but they do occur from time to time especially during storms.
A barometer is often used to measure atmospheric pressure. As the weight of the atmosphere changes, a column of mercury in a glass tube rises or falls in a barometer. Meteorologists define air pressure based on how high the temperature increases. If the temperature increase is 10 degrees F (5.5 degrees C), then the pressure is defined as 100 percent humidity.
At sea level, air pressure is about 1 kilopascal (kPa). At 10,000 feet above sea level, it is about 1/10th of a kPa. At 20,000 feet, it is about 1/100th of a kPa. At any altitude outside of this range, air pressure can be measured with a barometer.
Barometric pressures vary with weather conditions. A low pressure system will cause an area of low pressure, which will draw in warm moist air from the oceans and raise its temperature as it moves inland. This leads to higher humidity and lower wind speeds. A high pressure system will cause an area of high pressure, which will push away dry air from the oceans and reduce the temperature of the air as it moves inland. This leads to lower humidity and higher wind speeds.
Wind blows because there is friction between air molecules. The faster moving molecules are forced over the more sluggish ones, forming an arc across the sky. The direction the wind is blowing is called its gust factor.
This graphic depicts three popular methods for measuring atmospheric pressure: a mercurial barometer, an aneroid barometer, and a barograph. Even though we cannot see it, air exists and has pressure. It just so happens that the pressure varies from one place to another on Earth.
At sea level, air pressure is equal everywhere around us. But as you go up in elevation, the air gets thinner and there is more space between the particles. This means there is less pressure over your head and more pressure over your feet. Air pressure decreases as you go higher.
At high elevations, air pressure becomes very low which can cause problems for people who are used to living at lower elevations. For example, individuals who live at high elevations and then come down for the winter may have trouble breathing because the oxygen content of the air is lower than what they are used to.
At very high elevations, air pressure becomes so low that water turns into ice instead of being liquid. This is called "condensation." When this occurs on aircraft wings or tail surfaces, it can lead to corrosion.
The best way to protect against high-elevation pressures is by preparing yourself physically and mentally. Individuals should be aware of the risks of living at high elevations and take measures to prevent injury or illness.