methods and systems for detecting icing or incipient icing conditions external to a vehicle are disclosed . an apparatus in accordance with one embodiment of the invention includes a temperature sensor configured to direct a first signal corresponding to a temperature of an airstream , and a water content sensor configured to direct a second signal corresponding to a water content of the airstream . a processing unit can receive the first and second signals and , based on at least the first and second signals , provide an indication when at least the first and second signals taken together correspond to an at least incipient icing condition . accordingly , the system can be installed on aircraft to provide notice to the crew of incipient or existing icing conditions .