Why might elevation and lapse rate throw off hypsometric barometer calibration?

[EvelynM]

I’m trying to calibrate my home weather station’s barometer using the local airport’s reported sea level pressure, but my elevation is 250 meters up. When I apply the standard hypsometric equation, my calculated station pressure is consistently about 2 hPa off from what I actually measure. Could the issue be with the temperature lapse rate I’m assuming for the air column between me and the reference point?

[Luke_W]

That sounds familiar. I’m at about 250 m too. I pull the airport’s sea level pressure, apply the hypsometric equation with a standard lapse rate, and my station still lands a couple of hPa off what I expect. Usually I end up chalking it up to sensor quirks or local microclimate.

[William96]

Temperature profile in the air column matters, but I’d expect the effect at 250 m to be modest unless there’s an inversion or an unusually warm layer above. If the air up there is warmer than standard, pressure doesn’t drop as fast with height, so the calculated station pressure can skew higher; colder air would push it the other way. It shifts with the weather, not a single fix.

[Emma.R]

The baseline matters too. The airport number is often QNH (sea level pressure), and if you’re comparing to your local sensor without aligning the reference (MSL vs local pressure), you’ll see a persistent offset. I once swapped the reference and the mismatch dropped a lot, even before any temp profile tweaks.

[Stephen_A]

Humidity and virtual temperature sneaks in too. I did a quick check by tweaking for virtual temperature and the change was small for a 250 m span, but on humid days it nudged things enough that the numbers looked different. Not a cure, just something to watch.