A popular weather term for periods in the winter with cold stagnant air and inversions in the valleys, but fresh and warm air up in the mountains. Called "fake" because there is no cold air source other than what the inversion itself creates.
'Cold gloomy days and ice showers in the valley basin were actually caused by fake cold. Everyone outside the basin had enjoyed the warmth of spring for several days on end.'
by Bonneromics December 30, 2013