2- if its raining and temperature are low. What would be the temperature that indicates that a deice/anti-ice is required? same as engine anti-ice criteria ( OAT +10 or lower ) ?
If it is raining and temperature say +3°c or below and the fuel temperature is negative (e.g. -10°c) from a cold soak during a previous flight you might get clear ice forming on top of the wings, and it can be hard to tell whether it is iced or only wet. I guess some types may be more prone to this than others.