Hello, I'm the OUTDOOR PROFESSOR from DiscoveringTheOutdoors.com/
Here's your outdoor tip on using a barometer.
Turn on the TV or radio or maybe the Internet and you can get all the weather information that you need. There’s some truth to this statement, but an analog barometer is still an accurate weather forecaster for your specific location. Its job is to measure the rising or falling air or atmospheric pressure forecasting the weather usually about 12 hours in advance.
The pressure is shown on your barometer's dial in "inches" (inch Hg). The older barometers measured the pressure by the rise or fall of a column of mercury. The mercury barometer was invented back in 1643 by a pupil of Galileo named Evangelista Toricelli.
Meteorologists use "millibars" in charting atmospheric pressure and your barometer has a second scale or ring which reads in millibars (mb) in the United States. Standard air pressure at standard elevation (sea level) at 15°C and 45° latitude is 29.92 inches of mercury.
Most dial type barometers employ an air pressure sensor with limited sensitivity. The usual working altitude range covers only about 3000 to 4000 feet, but you need a barometer that has a sensor range factory set for your elevation.
You need toadjust your barometer before it’s used. A local weather broadcast will give barometric pressure for your approximate location. The adjusting screw is usually located in the back of the barometer and can be reached with a small screw driver to adjust your instrument to the broadcast reading for your elevation.
There will be a set hand on the front of your barometer to mark or place over the location of the black inside hand at the time you set the barometer. This outside set hand serves as a reference point so you can easily see if pressure is rising or falling.
You may want to take notes on the forecasting information that I’m presenting next, or look at the transcript of this program for a reference to forecasting you weather based on your barometer’s readings.
Barometric Reading - Forecast
Over 30.20"
Rising or steady - Continued fair
Slowing falling - Fair
Rapidly falling- Cloudy, Warmer
29.80" to 30.20"
Rising or steady - Same as present
Slowing falling - Little change
Rapidly falling- Precipitation likely
Under 29.80"
Rising or steady - Clearing, cooler
Slowing falling - Precipitation
Rapid falling - Storm
These are some general guidelines you can use when reading your barometer. The words on older barometers such as "stormy", "rain", "change", "fair", and "dry" are carry overs from the days when there was less scientific weather forecasting. These terms should not be used in predicting weather changes. You will not normally have large changes in the position of the indicating hand. Daily changes will usually run in a range of .02 to .10 of an inch on the barometer’s scale. The winter months will usually bring greater swings than in summer.
The actual number reading on your barometer is not as important as the trend the readings are taking. A storm is usually signaled by a steadily falling barometer. A rising barometer normally means sunnier skies ahead. Although very low readings (under 29.50 inches) can suggest a strong storm approaching.
Hopefully, this information will encourage you to watch your barometer more closely and enjoy seeing the effects of the changing air pressure in the outdoors.
This is the OUTDOOR PROFESSOR from DiscoveringTheOutdoors.com/
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References and Additional Reading
Understanding Air Pressure
http://usatoday30.usatoday.com/weather/wbarocx.htm
How a Barometer Works
http://www.sciencecompany.com/How-a-Barometer-Works.aspx
What Do Barometric Pressure Numbers Mean?
http://www.komonews.com/weather/faq/4347261.html
Nature Quotient.
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