Atmospheric pressure, altitude and vacuum tools
At altitude there is simply less atmosphere to push with.
Where the force comes from
A vacuum cup's holding force is the pressure difference across the pad multiplied by the sealed area. The maximum possible difference is bounded by ambient atmospheric pressure.
Altitude reduces the ceiling
Atmospheric pressure falls with elevation. At around 2,000 m it is roughly 80% of sea level; higher still and the reduction is greater.
A vacuum tool therefore has less available holding force at altitude, regardless of how good the pump or seal is. This is physics, not a defect.
Practical guidance
Working significantly above sea level, expect reduced margin and treat rated figures as further removed from reality.
Weather-driven pressure variation is small by comparison and rarely decisive.
Related
See what 45 kgf means.
Questions about this
Does altitude really affect a vacuum tool?
Yes. Holding force is bounded by ambient atmospheric pressure, which falls with elevation. At around 2,000 m it is roughly 80% of sea level, so the available force is correspondingly lower.
Does weather change holding force?
Barometric variation is small compared with altitude and rarely decisive. Surface condition matters far more than the weather.