WRAL WeatherCenter Blog

I enjoyed as a child living on the cost of Fla. having an aneroid barometer, and being able to tap it and see which direction the needle jumped. I learned how low was low and how high was high. A well meaning friend gave me a digital thermometer, the pressure on which at this moment shows "1026." That number means virtualy nothing to me. Your channel 5TV weather reports never seem to deal with the "digital barometer weather. In fact I don't think any other TV station I watch for weather reports do not either for that matter. Where can I learn what this number means? What is the top and bottom range? What is this high and/or low pressure digitally? I thank you in advance for your answer and await it in this column.

Posted May 16, 2007

MIKE MOSS SAYS:       Sandy,   The barometric pressure being read by your digital unit is the same information as your old aneroid barometer, it just appears that your new one shows the pressure using different units. I would guess the barometer you learned to use earlier was marked with pressure in inches of mercury, so that you probably recall numbers like 30.02" or 29.95" and so on, and as you mentioned most TV stations use these units for on-air reports. I would be surprised if your digital thermometer doesn't offer an option to in some way adjust the display units and change them to inches of mercury as well.

As for the numbers that it currently shows, you mentioned 1026 as an example. This would be in units called "millibars," also referred to as "hectopascals." You can easily convert between those units and inches of mercury by knowing that the average sea level pressure is 1013.25 millibars, or 29.92 inches of mercury. In other words, those two quantities represent the same pressure, and you can use the ratio between those two numbers to accomplish conversions in either direction.

You asked about ranges when using the millibar units. An especially low reading might be represented by the passage of the center of circulation that had been hurricane Fran in 1996, when the pressure at the Raleigh-Durham airport bottomed out around 977 millibars, while an especially intense wintertime high pressure system might produce a pressure approaching 1040 millibars.

Hope that helps, and that you enjoy your new instrument!


Please with your WRAL.com account to comment on this story. You also will need a Facebook account to comment.

Oldest First
View all