[Lowfer] ...effects of temp change on antenna current...

[JD]

A mechanical engineer wouldn't be able to help much; a meteorologist would 
be a better choice.

Whatever effect is at work, however, the change is probably not due to the 
volume of water in the air.  In terms of volume, the maximum amount of water 
that can exist as vapor in air is only about 4% under the most favorable 
conditions.  That's not enough to affect antenna capacitance to a noticeable 
extent.

Much more plausible is Mike's comment about soil properties varying with 
temperature.  Depending on the type of soil, its conductivity and dielectric 
properties can both be acutely influenced by the amount and physical state 
of water contained within it.

John