Rain can affect it, because it affects the natural surroundings around the bator, so that humidity from outside comes inside and that's where the bator is..Have to ask other than raising the humidity how can a lot of rain affect the hatch .? don't put a lot of time in monitoring heat and humidity. throw in the eggs turn it on and see how it comes out . If lower heat is one of the causes of insufficient fluid loss during incubation then I'm about to have a bunch of sticky chicks. Have to say it is nice when you do one thing and things get better . but of course the next set it all goes south again .