When we click on the
path profile link for WDKY in your TVFR, it's obvious that you have a significant bit of terrain roughly 1 mile from your location which is blocking your line of sight toward the WDKY transmitter. That amount of nearby obstruction is often enough to make reliable reception very elusive or impossible.
Changes in weather and the associated atmospheric conditions are known to change RF propagation... But predicting the exact effects with any precision is way beyond my math skills (and I suspect beyond the rest of the members of this forum).
I doubt, that wet antenna elements versus dry elements can be shown to have any significant variation in performance. I also doubt that using copper versus galvanized steel can be shown to be significant.
If you want to keep experimenting, I'd suggest you consider a build based on the VK5DJ software.
http://forum.tvfool.com/showthread.php?t=1106 Consider a 10 director cut for 575 MHz, the center frequency of real CH-31. Try tilting it up to aim at the top of the obstructing ridge.