The Use of Barometers as Weather Instruments

for Home Weather Forecasting

barometer

A barometer is a weather instrument that is used to determine the atmospheric pressure. As the air pressure either rises or falls, it is an indication of some type of weather change. Therefore, the barometer is an essential weather prediction device.

A water barometer, in its basic form, holds a container, usually made of glass, that is filled half-way, with water. The top of this container tube is open to the air or atmosphere. A small diameter tube is connected to the bottom of the water containing glass tube. As the atmospheric pressure rises or falls, the water within the glass tube moves in relation to that pressure. Measuring marks are sometimes placed in the water tube to determine where the water stands at any particular time.

In most barometers, there is a marker that can be moved up or down to mark where the water is standing at a particular time. The observer than can note the difference in the level of the water, thereby determining whether the pressure is rising or falling.

A mercury barometer is very similar to the water barometer except that it uses mercury as its base rather than water. The reason for this is that water volume can be compressed or expanded with pressure whereas Mercury is much thicker and unaffected by pressure. In other words, the mercury barometer is considered to be more accurate because the mercury does not change it's structure due to atmospheric pressure changes.

Aneroid barometers are non-liquid barometers that use a vacuum sealed case which is affected by the air pressure. A needle moves in one direction or another, exhibiting changes in the pressure on the sealed capsule. These are usually just hung on a wall and a person can observe them as they walk by. Again, a moveable marker can be placed over the current pressure reading to mark the current pressure so it can be compared to future pressures, thus determining whether the pressure is rising or falling.

In a general sense, falling atmospheric pressure usually indicates a more volatile change in weather whereas a higher or rising pressure, in most cases, means that the weather is less likely to change or is a calmer, more settled weather pattern.
Contemporary weather enthusiasts often use electronic barometers or precision digital barometers instead of the old glass tube types. Electronic barometers use electrical impulses to measure the air pressure and are often considered to be much more accurate.

A person can perform a fairly accurate weather change prediction simply by watching a barometer and using the following guidelines:

1. Rising barometric pressure often indicates that dry, calm or even cooler weather abounds.

2. Falling pressure often means that a storm, windy or rainy weather is inevitable within a few days.

3. Moderate or slowly falling air pressure would suggest that a low pressure ridge is close by indicating that your region may not be affected by the weather.

4. A small and rapid fall in air pressure means a short, brief weather change is near. These falls are often indicators or short periods of rain showers or increased wind. (For rain showers, you're going to need a "rain gauge")

5. A rapid pressure drop in a short time period indicates that a storm is likely to occur within a 4 to 7 hour period.

6. Pressure that is falling slowly and is sustained frequently means that a longer period of bad weather is approaching. If the atmospheric pressure starts to rise prior to the drop, this is an indication that the weather will be more pronounced or severe.

7. If the weather is fair and a rapid rise in pressure occurs or if there is above average pressure occurring, there is a good possibility that a low pressure cell is getting close. Usually, there will be an accompanying fall in the pressure and worse weather will be inevitable.

8. If the pressure rises rather quickly during a low pressure situation, there is likely to be a short time of fair weather.

9. If the barometer is slowly rising and is sustained, an extended good weather period is highly likely in the near future.

Barometers are made by a number of manufacturers and are a popular weather forecasting tool. Some of the more popular types and brands of this required weather instrument include the Nautical Brass Barometer which can be purchased for around $85; the Osprey Barometer for around $80 and the Cutter Barometer , with the price of about $200.

Whichever barometer you choose, remember that it is not the current reading that is important when reading barometers. Rather, it is the rate of change that is significant.