Ground conductivity probably explains why I always get stronger LF & MF reception during rain. It's my guess anyhow. For me the difference is far more than slight. Even HF improves for me during rain, but granted I stay on the low end of HF (<4000 kHz). I'm describing my reception, no transmitting.Ground conductivity has a major effect on the transmitting antenna tuning, something the engineer must keep on top of.