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Hi Alex, yes it is an interesting effect.
To an observer on the ground, the beam is visible within the "planetary boundary layer" which is the air from the ground up to a few hundred metres, maybe a thousand metres - which is full of microscopic aerosol particles. This layer typically extends to the cloud base which is usually 1500-2000 metres above sea level, and at this point there is usually an inversion layer. The air above the inversion is much cleaner, and the beam effectively disappears above that interface.
Hence its not uncommon to see a laser pointer apparently reaching the cloud base but not beyond that.
Over the upper Blue Mountains the cloud base is usually 1500-2000 metres above sealevel (having measured it on my paraglider), but can be higher in warm dry weather.
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