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How to read a barometer

Barometers are wonderful & traditional devices for forcasting the weather. Our Woodford range use no electronics or batteries, they show us changes in the air pressure on a daily basis and these in turn allow us to predict the weather. To answer a few basic questions we get asked very regulary we have made a short video looking at a Woodford barometer and how it is used to forecast the weather

How to read your barometer and forecast your local weather

Barometers are wonderful instruments for predicting your local weather; they do this by measuring the daily changes in air pressure. The barometer dial shows you how much and at what speed the pressure is changing.  With a few simple rules this allows you to predict changes in your local weather, generally the changes can be predicted 1-2 days before the weather occurs.

It is a fascinating and somewhat addictive pastime enjoyed by many, especially in our very changeable British climate, where only a generation or so ago, just about every home had a barometer hanging on the wall. For a more essential purpose sailors have used barometers at sea to help predict the coming weather, essential in the days before national forecasts and radio.

When your new barometer arrives (or in deed if you move house to a new part of the country), before using your barometer you need to calibrate it to your local air pressure. This is an easy process and needs to be done only once. For a quick guide to do this see our article on Setting your barometer

The barometer is made of several parts, the wooden surround, the mechanism and the dial.

The Surround– in the case of our Woodford barometers this is a wooden surround that is both decorative and holds the mechanism and dial in place. It is made from a stable wood with a veneer or from solid Oak, both are attractive and excellent materials for this purpose.

The Mechanism – In the case of our barometers this is produced in Germany, this is the traditional source of the highest quality engineered mechanisms. At the heart of the mechanism is a metal container, which is built in such a way that it compresses and expands with the changing air pressure, it’s movement is transferred to the needle on the dial, allowing us to see the changes magnified. The type of movement in our barometers is technically called an aneroid movement; you may come across this term in barometer books.

The Dial – Is the part of the barometer that shows us the readings, it looks a little like a clock face and has two needles. One is controlled by the barometer mechanism and the other is an reference needle which the owner moves to mark the place of the last reading, this allows you to see if the barometer indication needle has risen or fallen and by how much.

The dial has many markings and increments on it, the most important markings are measurements of the pressure; these are expressed in both imperial (inches) and metric (millibars) measurements.  This is the traditional expression used in metrology to show how much pressure the atmosphere is excreting on the Earth. There are often traditional words around the dial too, such as ‘change’ & ‘stormy’ these are very generalizations, what we really make our weather predictions from is the needle movement and pressure reading.

Using the barometer

A barometer mechanism is very cleverly made. It is designed in such a way that the indicator needs sticks, and does not move until you gently tap the glass. This allows you to watch as the needle moves to the latest pressure reading, enabling you to see how much the pressure has changed since your last reading and if it has risen or fallen.

Once the needle has moved you can mark its new position with the reference needle by turning the little knob on the front of the dial. If you check your barometer daily you can track the falling or rising air pressure and know how fast it is changing by the distance the needle moves each day, little or no movement means slowing changing or stable air pressure, while a large or sudden movement really means change to your weather is on its way.

So how do you predict the weather from the barometers movements?

As you track the changes in pressure, keep a mental note of what is occuring each day.

Very small changes in the position of the black index pointer up or down, are not terribly important, they indicate a fairly stable conditions; but a series of small changes in the same direction on consecutive readings taken at regular intervals will be significant as the pressure is steadily falling or rising.

The rising or falling trend of the barometer predicts weather 12-24 hours ahead of your current time. Here are some general weather predictions based on the rise and fall of the pressure.

Rising Barometer

  • A gradual but steady rise indicates settled or fair weather.
  • A very slow rise from a low point usually means windy, dry weather.
  • A rapid rise indicates clear and very windy weather.
  • A rise to a steady state of high pressure will usually indicates fine, warm weather in summer and clear, cold weather in winter.

Falling Barometer

  • A gradual but steady fall indicates settled, wet weather.
  • A very slow fall from a high point means wet, unpleasant weather without much wind.
  • A sudden fall indicates sudden rain or snow, high winds or both.
  • A fall to low point, usually rapid, should be regarded with serious caution because very high winds and storms may occur.
  • Lower pressures are regarded as deep depression weather systems – pressure and the attending weather is unstable.

If in doubt, here is a simple rhyme to make a basic prediction:

“Rising better, falling wetter.”

 We do hope you gain many interesting hours by using your aneroid barometer, they are fascinating and rather addictive. If you have any questions then please get in touch.