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My city's altitude is almost 950 meters, yet the weather stations provide a read of 102.14 kPa which is around 1 atm!

Shouldn't the pressure be a function of elevation?

I doubted that the data provided could be wrong, so I checked New York and got almost the very same results.

All reading are very close to 30 in.Hg (around 1 atm), yet the elevation varies from 0 to 550m. So, what is going on?

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The reported pressures are sea level pressure. For stations not at sea level (most of them), they can be corrected to sea level through use of the hypsometric equation. The reason the values are reported as sea level pressure is so that pressure values between stations can be interpreted in meaningful ways. See for example a typical sea level pressure plot:

sea level pressure

In order to produce such a plot, you need pressures on a common reference plane, which is often mean sea level or some other reference pressure level (e.g. 850mb, 500mb, 250mb). This is why stations report sea level pressure rather than actual station pressure. This also has applications for aviation, where aircraft operating below a specific altitude (18,000 ft in the US) have to reference their altimeters to a common value regionally and must know the local sea level pressure.

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  • $\begingroup$ Great answer @casey, I have often wondered this myself. $\endgroup$ – user889 Nov 29 '14 at 22:38
  • $\begingroup$ I never wondered this at all ;-) But now I think about it, yes it would have to be at some reference altitude rather than individual local altitude. $\endgroup$ – smci Nov 30 '14 at 8:43

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