I did window cleaning for 15 years. without sounding too blunt, this was where the proper window cleaners shone through.
Professional ones do it all year round. Cowboys did it cash in hand in the summer only with no insurance etc...simple as that. I can’t imagine it’s changed much.
A lot offer other elements like gutter cleaning. This helps fill in some gaps that may appear from customers who only want their windows done every 2 months instead of one during winter.
No your skin is waterproof. I got rid of all my domestic customers but when I did have them I was out every day unless the rain was torrential. It rarely rains non stop for the full day so at most your dodging heavy showers sitting in the van.
Personally I had hardly any change frequency or cancel over winter. That's all down to educating the customer. Any that did got binned and replaced immediately as I always had a stream of new enquiries coming in.