Sysiphus wrote in :

Well, rain is an attenuator. Perhaps the signal you are looking for is
being attenuated by the rain, and, that attenuation plus the noise
generated by the power lines=lower SNR.

I see it all the time(not in SW bands, I am in Satellite
Communications[8GHz], but the theory has to be the same) Rain attenuates
desired signal, lowering C/Kt



True, but the effect of rain on LF and HF signals are negligible. This has to
do with the significantly longer wave lengths of the LF/HF signals especaily
when compared to that of microwave. As the wave length of the signal
approaches the size of the rain drops, attenuation increases.

Take a look here :

http://www.telesat.ca/satellites/tra...ttenuation.htm


--
Panzer