Flood frost

For Ireland, it's been really cold these last few days and especially nights.  I've been anxious about snow and being either stuck on our mountainside and unable to eaqrn my salt or unable to get home after work.  40km is hefty enough of a commute in a car and I have done it, there and back, by bicycle, but I can't walk home if the roads are unsuitable for cars.  I was delighted this morning to go out to the car in the dark to find it frost-free.  The cold snap is over, I thought.  So imagine my surprise when I drove the 300m along and 30m down our rough bohereen to find the surface all icy at the bottom on the county road; and all the way into work.  If we discount the idea that our yard has sent up a bollupe of ionising radon gas that warmed the very air, it must have been an example of flood frost.  I can do no better than clip wikipedia "A related effect is flood frost which occurs when air cooled by ground-level radiation losses travels downhill to form pockets of very cold air in depressions, valleys, and hollows."  I've never seen this phenomenon so clearly present.