For the past two nights the grass minima here has been 6.7C lower than the air minima. It is usually about 4 - 5C lower. Is the high difference something to do with the saturated ground and high evaporative heat loss under a clear sky? The soil here is very heavy clay.

On Sunday, 3 July 2016 13:12:28 UTC+1, Scott W wrote:
For the past two nights the grass minima here has been 6.7C lower than the air minima. It is usually about 4 - 5C lower. Is the high difference something to do with the saturated ground and high evaporative heat loss under a clear sky? The soil here is very heavy clay.

I would have thought it had more to do with the wind. Recent nights have been a little breezy and it could be that this has made the screen minimum a little higher than would otherwise be the case but had a smaller effect on the grass min. If the wind had been stronger it would have raised the grass min as well. I'm not entirely convinced by this but it's just a thought.

Tudor Hughes, Warlingham, Surrey.