Barometers

Barometers

Know which way the wind blows: Forecast the weather by gauging changes in atmospheric pressure.

With a simple aneroid barometer, available at a local hardware store or marine supply center, you can make fairly accurate short-range weather predictions for little money. Generally, when the barometer is high and rising, it means high pressure is approaching. High pressure systems typically are associated with fair weather – light and variable winds, dry air, and temperatures below seasonal averages. When the barometer is low and falling, it typically means low pressure is on the way. Law pressure systems tend to bring inclement weather – strong winds, high humidity, clouds, and storm fronts.

An aneroid barometer has one pointer, similar to the hand on a clock, which measures atmosphere pressure in inches of mercury and another pointer which is used to reference pressure changes. Rising pressure causes the reading pointer to move clockwise, while falling pressure causes it to move counterclockwise.

Once or twice a day, the reference pointer should be placed to correspond with the reading pointer. Over the course of the day, you can track pressure changes by noting how the reading pointer moves in relation to the reference hand.

Park of the Hudson River, New York. Photo : Elena

To ensure accurate readings, aneroid barometers, and even some electronic barometers, occasionally need to be calibrated. A call to the local branch of the Weather Service or listening to the weather report on TV provides the current pressure adjusted to what it would read at sea level. Adjustments should be made on days with settled winds, which usually indicate the pressure is changing slowly.

Many amateur forecasters find useful the following chart, which bases its weather predictions on barometric changes and wind direction. However, meteorologists caution these are general rules that don’t hold true for all locations and situations. For example, west winds off the Great Lakes can bring terrible lake effect snows even when the barometer is high. Similarly, in the Northeast near the Atlantic Ocean, a sea breeze can bring cooler air, clouds, drizzle, and fog when the pressure is high.

Be Your Own Forecaster

Basic barometer reading for amateur meteorologists can fool you, but generally they can help you to find out what weather to expect.