Home (or personal) weather stations have gained popularity in homes and businesses worldwide. As will be illustrated, most of these instruments measure a surprisingly wide range of weather variables.

The following table lists the primary atmospheric elements weather stations measure, as well as the instruments used to measure them:

When you think about how the weather is measured, it is actually not just one, but a combination of measured variables. Combined, these variables form the atmospheric conditions we experience as a specific type of weather at any specific time.

The most common elements measured by a home weather station are temperature, humidity, wind speed and direction, rainfall, and air pressure. 

(You will notice that, in the table above, Light Intensity and UV Index are also mentioned. Although more advanced weather stations are capable of measuring these parameters, they are not as critical to weather and forecasting as the other six variables.)

To better understand them, we will look at each of these different elements that make up the weather. Under each category, we also look at the different instruments used to measure it, as well as how each instrument measures that specific aspect of weather.

Humidity is the amount of moisture present in the air and is measured by a hygrometer. A variety of different hygrometers exist, but again I will just focus on the two most important ones to stay on point.

The psychrometer is a well-known earlier example that uses two thermometers (one being covered with a wet cloth and the other in open air).

The bulb of the thermometer covered with the cloth will give a lower reading due to the evaporation of the moisture on the cloth. The rate of evaporation, in turn, depends on the amount of moisture present in the air. The different readings between the two thermometers are then used to determine the relative humidity of the air.

Rainfall is the amount of precipitation measured in a specific area over a certain period of time and measured by a rain gauge.

Professional weather stations use a cylindrical funnel with an aperture of 8 inches (203mm), which is placed about 12 inches (300mm) above ground level. It can normally hold up to 1 inch (25mm) of rainfall.

After a 24-hour period, the content is collected and poured into a calibrated glass for accurate measurement, while the empty cylindrical funnel is repositioned in place to record the next 24 hours of rainfall.

Naturally, not all rainfall gauges can be manned and emptied regularly, especially when it comes to personal weather stations and weather stations placed in remote areas. As a result, almost all modern homes and remote weather stations use Tipping Bucket Rain Gauges.

Tipping Bucket Rain Gauges have the advantage of recording rainfall automatically and never needing to be emptied. They consist of two buckets that are balanced on a fulcrum (and work in a see-saw action).

A funnel collects the rainfall, which is collected in one bucket. Once the bucket reads a specific amount of rain, it tips and empties its contents into a runoff area. As it tips, it triggers a switch that sends a signal to the base station to record the reading. At the same time, the empty bucket on the opposite side lifts into position to record the same amount of rainfall before it also tips; the measurement is recorded, and the process is repeated.

Wind speed is simply the rate at which air is moving at any specific location and is caused by a difference in air pressure, as air flows from an area of high pressure to an area of low pressure. The instrument used for measuring wind speed is called an anemometer.

The most well-known and commonly used anemometer is the 3-cup anemometer (or 4-cup), where cylindrical cups are attached to horizontal arms that pivot around a central pole.

As the wind speed increases, the cups start rotating faster. By measuring the speed of this rotation, the wind speed can be calculated. The actual measurement can be done in more than one way, but all are based on the speed at which the cups are rotating. 

There are other ways of measuring wind speed, like using a hot-wire anemometer or tube anemometer, but they are not important for normal everyday wind speed measurement.

Wind direction obviously refers directly to the direction of air movement (wind). It may not be as obvious as you think, though. Wind direction refers to the direction the wind is coming from, not the direction it is blowing in. (This means that when the weather reports refer to a southerly wind, it means it is coming from a southern direction. Many people understand this the other way around.)

Wind direction is measured predominantly by a windsock or wind vane. Windsocks are often seen at airports, but the weather vane is used on a regular basis in professional and personal weather stations.  

Most of you know what a weather vane looks like. Very often seen on top of tall buildings, it consists of a horizontal pole spinning freely around a central axis with an arrow (or similar pointing device) on the one side, and a big flat vertical surface on the opposite side that responds to any changes in wind direction.

Air Pressure (also called barometric or atmospheric pressure) is the force exerted by the weight of the air around us. To put it another way, the air around us has weight, which creates pressure on the surface below it.

Air pressure decreases with altitude because there is less air above pressing down. This means the air closer to the ground is denser, while the air higher up in the atmosphere is much thinner.

(This is the reason jet airliners fly at such high altitudes of around 30 000 feet. The low air density allows them to fly much faster and more economically through the thinner air, keeping fuel usage much lower than it would be at low altitudes where they would have to push through denser air. It keeps them out of more turbulent air closer to the earth’s surface as well.)

The instrument used for measuring air pressure is called a barometer. There are basically two kinds of barometers. The Mercury and Aneroid barometers.

Mercury barometers date back centuries. They consist of a glass tube partially filled with mercury. It is placed upside down in a container (reservoir), also containing mercury. The container is exposed to the surrounding air.

As air pressure increases (gets heavier), it pushes down on the mercury in the reservoir, forcing the mercury inside the glass tube to rise. This change in mercury levels is measured, and air pressure can be calculated as a result. Naturally, as air pressure drops, the opposite occurs.

As mercury is very poisonous and the setup requires a fairly controlled environment, this kind of barometer is not a very safe and practical solution.

Aneroid barometers solve all these problems and are used in almost all modern weather stations (and even in your smartphone!) They consist of a partially vacuumed sealed metal container. This is attached to a spring and levers, which are connected to a needle or electronic measuring device.

As the air pressure increases, it causes the container to contract, causing the attached spring/levers to expand or move, which is registered by the measuring device and either displayed or transmitted to the base station. When the air pressure decreases, it causes the container to expand, causing the opposite reaction, which is also measured and recorded.

Now you have a clear understanding of what variables a weather station measures, as well as which instruments are used to measure them and how they are measured.

Also, take note that not all home/personal weather stations can measure all these variables. Normally, they can contain any combination of measuring tools. (The more comprehensive weather stations come standard with all of these measuring capabilities, though.)

Some personal weather stations even read more variables than the ones mentioned in this post, like solar radiation and soil moisture. These are advanced functions and not a necessity for the majority of your weather measuring requirements. 

Until next time, keep your eye on the weather!