ANTI-ice.
The clue is in the name. Anti ice systems are intended to prevent the formation on ice in the first place.
Exactly what systems should be used when is type dependant, but generally in the 'always turned on' category (for things like pitot heaters) or the 'turn on during flight conditions that could cause ice to form' category for major pneumatic or electrical consumers such as aerofoil protection.
Not based on forecast met, but on actual conditions. Something like (visible moisture or vis<1mile) and (temp<some value).
pb