Why on a sunny day, an aneroid barometer would indicate stormy weather when carried to the top of a mountain?

Question

Why on a sunny day, an aneroid barometer would indicate stormy weather when carried to the top of a mountain?

Answer 1

The answer above is precise.

Answer 2

Higher elevations have a lower pressure.  This is how an aircraft [or a hiker's] altimeter works.  It detects the change in pressure as you increase in altitude.  In an aircraft, the pressure at a known altitude is used to "calibrate" the altimeter.  This corrects for non-standard pressure.  You do a similar thing with an aneroid barometer when you set "current" conditions.  So, when you climb to the top of the mountain, the pressure is less than at the base of the mountain, and the barometer indicates a lower pressure than that you specified to be the "current" condition.

So, what does that have to do with a storm?  Stormy weather is generally [always?] associated with lower pressures.  The barometer indicates that the weather will be stormy because of the decrease in pressure.  And, since you climbed a mountain and the pressure decreased, it indicates a storm.