WiFi signal

Does anyone know if weather can have an adverse effect on a wifi signal. My laptop sits on the end of the butcher block that we have in our kitchen. Works just fine and normally no problem with the signal, however when we have high humidity, the signal strength drops right of and the internet crawls a snails pace. If I move so that a particular wall is no longer in the way, then all is fine. This only seems to happen when the humidity goes up though, any ideas :-? :-/ :-?
Matt
Matt