Proudpilot - I think you will find IO540s question was a little tongue in cheek - if you will reflect we know that if there is visible moisture in below freezing conditions then that COULD cause icing - however that is not a forecast it is a statement of the actual conditions. In reality most area forecasts in the UK and Europe "warn" of the possibility of icing when often there is none. Forecasting icing conditions is still a very inexact science; it is true that if you never fly in conditions where the outside air temperature is below freezing and substantially true that if it is below freezing but there is no visible moisture you will not encounter icing but it is equally true that conditions below freezing and with visible moisture will not result in icing.