When barometric pressure in your area drops, it typically signals increasing clouds or an oncoming storm. You have several options for finding the barometric pressure in your area: you can build an inexpensive wet barometer called a storm glass, purchase a barometer and check readings daily, or review any one of the multiple weather websites that display local results for barometric pressure.
Atmospheric Pressure Definition
After centuries of measuring air pressure, meteorologists and scientists know that the weight of air – atmospheric pressure – equates to 29.92 inches of mercury at sea level. A barometer measures the changes in the air mass over a specific area that signals changing weather patterns. Low barometric pressure means the air mass over the area measured is decreasing and indicates a storm or low-pressure system is moving into the area.
Make a Storm Glass
Most modern-day barometers use a sealed vacuum tube of mercury – because it is 14 times heavier than water – measured at intervals to indicate changes in the weight of the air, or air pressure over a specific geographic area. However, you can make your own storm glass with supplies at home, using a procedure provided by the National Weather Service. You’ll need a foot-tall glass or beaker that has straight sides, a foot of clear plastic tubing, a plastic ruler, chewing gum or modeling clay, water, red food coloring and a log book to record measurements.
Sciencing Video Vault
Assemble the Storm Glass
Set the ruler inside the glass or beaker and tape it to the side, facing the ruler out so that you can easily see its measurements. Fill the container approximately halfway with water, and tape the tube to the other side of the ruler. Place the tube low enough so that the end is in the water, but don't let the bottom of the tube actually touch the glass. You can tape the tube to the ruler. Add a drop or two of red food coloring to the water outside the tube and mix it in completely. Draw liquid into the tube by sucking on it, trapping the liquid about two-thirds up the length of the tube. Cover the tube’s top with clay or gum.
Take Daily Measurements
Record the height of the water in the tube using the ruler. Check the height of the water in the tube against the ruler at the same time each day and record changes in a log book. Note the changes recorded to the changes in the weather. When the water in the tube drops, this indicates an incoming storm or decreasing air pressure.
The National Oceanic and Atmospheric Administration maintains an online Weather.gov site into which you can type your street address and city. Enter your location as indicated in the top left field on the site to find the weather report for your area. After clicking on the word “Go,” it will take you to a readout of the weather for your area. Note any special weather statements or warnings of storms, wind changes or heat waves. In the area below that, it displays the current temperature, humidity, wind speed, barometer pressure, dew point, visibility, heat index and the last time the page was updated.