The barometer is an instrument used in meteorology to measure atmospheric pressure and traditionally utilises water, air or mercury to present its results, although these days electronic barometers are also available. Like all meteorological applications, the barometer is used to formulate an accurate forecast of forthcoming weather. But what exactly do these readings mean to us?

There is actually a lot we can figure out just from studying atmospheric pressure readings. A single reading can be useful but studying them on a regular basis will help you build up a much more accurate knowledge of how the weather will be changing in your area.

There are however a few factors that need to be taken into account before analysing your readings. Both temperature and altitude will affect your readings and they will need to be adjusted to accommodate these effects. Higher temperatures reduce the density of liquids so it is best to use a thermometer in conjunction with a barometer so that both readings can be cross-examined. Altitude is also important as pressure decreases the higher up you are above sea level.

Generally, a high reading will indicate clear, dry weather. This is because the density of high-pressure air causes it to gradually fall, warming as it does so. Warm air also prevents clouds from forming, which means a clear day will be on the way.

Conversely, a lower reading signifies a higher chance of rain. When air is less dense, it rises and cools. If there is moisture in the atmosphere while this is happening, it is very likely that it will form clouds which will then descend in the form of rain.

But there is only so much we can tell from a single reading and they merely suggest what type of weather is likely to occur, rather than providing a definite forecast. Studying trends regularly over time is a much better way to build an accurate picture of how the weather is changing. The general rule is that a steady rise shows that the weather will be clearing up, while a steady drop means rain is on the way, and if it drops rapidly there could be a storm coming.

You can also get an idea of how close these changes in weather will be taking place by how quickly the pressure changes. If the pressure drops slowly but moderately it may be happening in a surrounding area while a small but quick, regular change shows that it will be closer to home. A particularly dramatic drop means that a storm will probably be approaching in just a few hours.

If a large drop happens slowly but consistently then this is warning you of a long period of bad weather on its way but this also works the other way as a slow but large rise means a long period of warmer weather is coming.

Quickly rising pressure that starts from a low reading shows a short period of fair weather approaching but if the same kind of rise occurs when the weather is already fair, it actually means a drop isn’t far away so you should prepare for a rainy day.

Barometers have proven to be quite an accurate way of predicting weather and are an essential part of any weather station. If you follow these patterns you should soon be able to start forecasting weather for your own region with ease from the comfort of your own home