Turin
Not always true especially in high pressure and clear skies you can find that the air above the ground increases in temperature
I have had -2 on the ground and plus 8 at 8000 feet
In flight ice will normally slowly vaporise off over time depending on how much you accumulate!
Even with an ice capable aircraft and boots! Blowing it off the leading edges doesn't take it off the airframe
I had one occasion after leaving a front I asked for a temporary descent out of airways to loose the airframe ice as I had a long way to go and substantially reduced airspeed!
After it melted off I climbed back into the airway and carried on )
Pace