How to Track Changes in Barometric Pressure

Purchase a good barometer. These range in price from a little under $200 up to $500 for a high-quality instrument. More expensive barometers often feature temperature compensation that cheaper barometers may lack. This makes for more accurate readings, because changes in temperature can affect the mechanisms that are detecting changes in pressure. Cheaper barometers will introduce larger inaccuracies in pressure readings if exposed to large temperature fluctuations. Another factor to consider is altitude calibration. Your barometer should be calibrated to the elevation where you'll be taking the readings. The most common calibration ensures accuracy from 0 - 1070 m elevation. If you are taking readings at a high altitude, make sure your barometer is calibrated for that altitude.

Record barometric readings at regular intervals. Your barometer may display pressure in inches or millimeters. These are, of course, units of distance, not pressure. These represent millimeters or inches of mercury (Hg), and a reading of 760 mm Hg is equivalent to the amount of pressure that a column of mercury 760 mm high would exert. The barometer might use a unit called a kilopascal (KPa). The standard atmospheric pressure at sea level is 760 mm Hg, which is equal to 29.92 inches Hg, or 101.3 KPa. This amount of pressure is also known as one bar, or 1,000 millibars. You can use any of these units to track pressure changes. Just make sure you consistently use the same units and apply the appropriate conversions when comparing to other data.

Compare your readings to historical weather data to get a sense of overall meteorological patterns. The National Climatic Data Center, a division of the U.S. Department of Commerce, maintains an enormous archive of weather data. You can access climate maps, showing distributions in average pressure throughout the U.S. during specific time intervals, or charts documenting changes in pressure in a specific area over time. Much of this information is available for free and can easily be accessed online. Some information, including archived data from earlier years, can be ordered and may entail a service fee.