This post may contain affiliate links. Buying something through these links doesn't cost you anything and helps support Know Prepare Survive. For some light reading, check out our affiliate disclosure.
These days, most of us get our weather forecasts from other people.
Whether it’s from the television, computer, or smartphone, this information comes from another source.
Therein lies a weakness. When you most need to know the weather, you may not be able to connect to the weather forecast provider.
No, I’m not talking about if the grid goes up in flames. EMP attacks, solar flares, and a loss of infrastructure could cause this problem, but are all quite unlikely.
The weather itself can knock things out temporarily. Lightning does strike twice, as evidenced by how Puerto Rico was struck by both Hurricane Irma and Maria.
You are at your weakest when you are rebuilding after a natural disaster, and so it is the most important time to be able to tell what the weather will do, before it happens to you.
Fortunately, there are devices available which can help. One of these is a barometer, which measures barometric pressure.
What is a Barometer?
The barometer was invented in the middle of the 17th century and remains in use even by meteorologists who have access to the latest and fanciest technologies.
If you are familiar with altimeters, they are the same device, just with a different method of reading and a different purpose.
Typically a barometer is kept in one place and is used to read the barometric pressure of the surrounding atmosphere.
What is Barometric Pressure?
Also called atmospheric pressure, barometric pressure is how much the air above you weighs. Air has mass, even if it’s not very much, which gives it weight.
From Aristotle until Galileo, educated persons thought air was weightless, so if you ever feel cocky and want to brag about knowing something those two did not, there you go.
But air does have weight, and barometers measure that weight.
Atmospheric pressure changes as weather fronts move around (hot air rises and cold air falls), so by tracking the change you can have a rough guess at forecasting the weather.
Types of Barometers
While the principle stays the same, the way we measure barometric pressure has changed quite a bit over the centuries.
The original type of barometer used water. It is easy enough to make one on your own, especially if you are a glass blower.
Take a glass container that is sealed at the top and fill it half full with water (perhaps seal it AFTER adding the water), and make sure there is a spout near the bottom that heads up and has a narrow opening to the air.
As the air pressure changes, it pushes down more or less on that water, which results in the water inside the glass moving up or down as well.
Mercury barometers were the next step in barometer technology. They are a glass tube filled with mercury, open at the bottom to a dish of mercury exposed to the air. Mercury can be dangerous, so these types are no longer recommended.
Aneroid barometers were invented in 1844. These use a metal alloy, typically from beryllium and copper, which expands and contracts in response to changes in the atmospheric pressure.
The changing size of the metal bit moves mechanical levers to measure the change.
Stick a diaphragm on that wire, and atmospheric pressure will change the electrical resistance.
The electronic barometers are tiny enough to fit almost everywhere, even in watches!
Watches which contain barometers are often known as ABC watches, because they typically also have compasses and use the barometer as an altimeter as well.
If you do not want to have access to weather forecasts on your hands (why wouldn’t you?), you can find tabletop or wall mounted barometers for sale as well.
Most are digital though some are the old style, with a dial face. Digital barometers often also contain other atmospheric sensors so they can measure temperature and humidity as well, and may be able to forecast the weather for you.
Who Uses/Needs a Barometer?
The Weather Man is the most obvious answer, but anybody who needs to forecast the weather without access to other people need barometers as well.
People who live in an area prone to weather related natural disasters such as tornadoes and hurricanes can heavily benefit from owning a barometer and knowing how to use it.
If you live in the woods and walking to your neighbor takes more than a one minute walk across your yard, a barometer might be useful as well. If it takes a day’s worth of travel, definitely own a barometer. Or buy a better truck.
If you have a concern about the grid disappearing then a barometer would be useful too.
People aboard a ship often use barometers as well, as a boat is more susceptible to fluctuating weather than is a house.
Why is it Useful?
A barometer helps you forecast the weather!
Pressure systems are one of the simplest and still best ways to predict the weather, at least in the short term.
Knowing the temperature, humidity, and other atmospheric values can make things more accurate, but a coming storm can be detected by a simple change on your barometer.
How to Read/Use a Barometer
Barometric pressure is often expressed in one of several units, including pascals (Pa), millimeter of mercury (mmHg), bar, torr, and pounds per square inch (psi). Pascals and mmHg are the most common units in use currently.
A water or mercury barometer will show you the liquid and have indicators to show the measurement. Just look across the bottom of the meniscus to the measurements.
If you do not know what a meniscus is, that is when a liquid curves to meet the edges of its container. Measure from where the liquid is flat.
Traditional barometers have a dial, much like your speedometer. Just read the mark at the pointer. Often multiple units will visible on the same dial, so pay attention to the guide on the barometer itself.
Digital barometers are easy, and output the pressure directly. Often you can change the units displayed.
There are easy and difficult ways to use this information. If you want an exact forecast you can use other measurements, such as temperature and humidity, perform some calculations for your altitude, and do some other math to get a forecast.
For a quick and dirty forecast, watch whether the barometer is increasing or decreasing in pressure.
Increasing pressure often means that the air is warming and skies are clearing. The weather should be nice.
Decreasing pressure often means that the air is cooling and moisture is condensing in the air, forming clouds. Prepare for rain!
The rate of change affects the forecast as well. The bigger the change in pressure, the more the weather will change. The faster the pressure changes, the more quickly the weather is moving in.
If the barometric pressure drops quickly and far, watch out! There’s a storm incoming!
Modern digital barometers often show the recent pressure highs and lows to help you figure this stuff out.
A Note on Altimeters
An altimeter is a barometer which outputs the altitude instead of the pressure. They can be helpful in navigating mountainous or hilly terrain, but can also give a rough guess of the coming weather.
If you need to use an altimeter as a barometer then you just invert the recommendations. A drop in barometric pressure registers as an increase in altitude, so keep that in mind.
Since they are affected by both altitude and weather, it is wise to recalibrate your altimeter at least once a day, to a known correct altitude reading.
Sometimes you just do not have access to the television or internet, but still need to know whether the weather headed your way will be clear skies or a storm. A barometer is a simple yet effective device which can help keep you informed!