there is too much snow ad ice to worry about gritting, i have lots of salt, but i aint used any of it....
just go and wash the windows and stop worrying.... snow on the ground... temperatures above freezing during the day...(otherwise your gear would freeze)...
so its fine, it wont turn to ice until night time.... and if your customer asks what the hell are you doing...
tell them its unsafe to work with ladders in this weather.... then tell them not to worry , it di water and will dry clear...
in fact its the perfect time for you to get out there with your new , hi-tech safe way of window cleaning.