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Hi Dina,
I always lived at elevations closer to sea level until moving to Utah about a year ago. Do barometric pressure measurements here report actual or adjusted values? Does a report of 30 inches of mercury represent a true 30 inches or is this adjusted for Utah's higher altitude and lower air pressure? One of my engineering references detailing a standard atmosphere table shows that normal pressure at sea level is 29.92 inches of mercury. This decreases to 25.84 inches at 4,000 feet and 24.90 at 5,000 feet. However, most weather reports associated with normal conditions here report pressures around 30 inches of mercury, not 25. What's up with that?
Thanks for the explanation!
Regards,
Andy B.
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What is up with that? No, seriously, here's the deal. When you see Barometric pressure on weather map or just visiting online to see what the pressure might be at the airport, the values have been adjusted. Pressure readings are adjusted to sea level. Like you said, pressure decreases as you go up. If were to refer to the actual station pressure in Salt Lake at something like 24.90 inches of Mercury, not only would everyone be confused but it would alter the continuity of weather information.
One reason for the adjustment to sea level is for the purpose of the analysis of weather. We analyze weather across the state and the country using parameters like pressure, height falls and rises, moisture, just about anything really. We use an equation to obtain the correct sea level pressure reading (another reason why math is so important in meteorology).
If we were to use actual pressure, and our pressure here was so much lower than everywhere else, our map would look like it had a constant area of low pressure on it which would be false! By standardizing the pressure, we can look at the U.S. on the same level (sea level) to figure out what types of weather are happening around the country.
The main thing to watch for when you listen to a weather report as far as pressure goes, are the falls and rises. It is these type of changes that can indicate a change in weather and also give people problems if they are sensitive to pressure changes. People with Fibroymyalgia often state that pressure changes trigger some of their body aches along with Arthritis patients. There's a whole other field of this called Biometeorology where scientists study how weather affects the body.
You can't avoid pressure changes, it happens all around us, but you can just be aware of when a storm is coming and if rest is a better solution for you, then go for it.
Answered by KSL Meteorologist Dina Freedman.
