What the heck is a warm nose?

Note the red line at the btm as it moves from close to zero Celsius to warmer temps and then back to freezing with height!

In weather terms, a 'warm nose', in the winter time, is a layer of air at about 850 millibars or 5000 feet that is warmer than either the freezing air above or below it. It can cause problems associated with any precipitation that might fall through it resulting, for example in snow reaching that level and then melting only to begin to refreeze as it get closer to the ground. The result, generally, is some form of sleet, but can become freezing rain if other conditions permit. So when a weather forecaster is talking about a warm nose of air moving into colder air, he or she is tacitly warning the viewer about possible forms of precipitation that would be different from rain or snow, i.e. some form of ice.