Frost-free Warlingham
 

List night was a very good example of what can happen on the higher parts of The Downs in a light anticyclonic southerly and a clear sky. The min at Gatwick (12 miles SW) was -5° and even Heathrow (about 18 miles WNW) had -3°C, yet here the screen min was +1.5°C and almost constant throught the night. No air frost but a heavy ground frost that even whitened the roads. There was a very light S'ly throughout. I have noted this sort of thing before on a number of occasions when the conditions are right. Normally the minima here are lower than Heathrow, clear sky or not, but Gatwick ("Fogwick") is usually lower.

Tudor Hughes, Warlingham, NE Surrey, 557 ft, 169 m. TQ 3516 5955

Frost-free Warlingham
 

On Wednesday, 31 December 2014 17:02:30 UTC, Tudor Hughes wrote:
List night was a very good example of what can happen on the higher parts of The Downs in a light anticyclonic southerly and a clear sky. The min at Gatwick (12 miles SW) was -5° and even Heathrow (about 18 miles WNW) had -3°C, yet here the screen min was +1.5°C and almost constant throught the night. No air frost but a heavy ground frost that even whitened the roads. There was a very light S'ly throughout. I have noted this sort of thing before on a number of occasions when the conditions are right. Normally the minima here are lower than Heathrow, clear sky or not, but Gatwick ("Fogwick") is usually lower.

Tudor Hughes, Warlingham, NE Surrey, 557 ft, 169 m. TQ 3516 5955
Same here in N. Bristol on my S. sloping semi-rural road.
The two previous nights we had all three conditions for a mild night air frost-absolutely no wind, clear skies, and a cold stagnant air mass to start with.
Had we had some wind drift or cloud coming over the frost would have disappeared. As it was we only got down to -1.5C for about three hours each night-my first air frosts since April '13. Last night a v. gentle S. drift kept us up to 3.5C under clear skies.
From the looks of the MRF I don't expect a chance of an air frost for at least two weeks.