The function BIS_fnc_paramWeather expects values from 0 to 100 which is uncommon and not used by any other weather command/functions. They all expect values from 0 to 1.
The line of code responsible for this is the following:
[_overcast * 0.01] call bis_fnc_setOvercast;
So there is no real reason to expect values from 0 to 100 and it would match to other funtions when the "* 0.01"would be removed