One of the problems in Winter for homeowners, apart from having to clear footpaths and driveways, is that in periods of heavy snow, although it looks pretty it can also sometimes block your view when it settles on windows and window frames.
Your window cleaner may still be able to keep your windows clean, especially when using a water fed pole system, and especially if they use a hot water system, but if your window cleaner still uses traditional methods to clean windows, you might find that when conditions are slippy then the use of ladders may not be safe, and therefore widows don’t always get cleaned regularly.
Also, in extremely cold conditions its not unknown for windows to ice up. Therefore, if the exterior glazing can be accessed from the inside, i.e. through side opening windows, snow and ice may be able to be removed using a long handled brush and some warm water or de-icer. Ice scrapers can also be used but obviously you should always avoid leaning too far out of windows. Better safe than sorry.