On Wednesday, 2 December 2020 at 16:44:15 UTC, Norman Lynagh wrote:
Metman2012 wrote:

On 02/12/2020 10:55, John Hall wrote:
In message , Vidcapper
writes
On 01/12/2020 09:46, Bernard Burton wrote:
"Keith (Southend)" wrote in message
...
This November I only had two 5 minute logs (10 minutes) of 0.0°C, is
this classed as an air frost or should it be -0.1°C?

My thinking is not, so no air frost reported for me for the whole
month.

Keith (Southend)

Yes Keith, temperature needs to be below zero to warrant a frost


Try convincing the local car owners of that, though!


The temperature of car windscreens, and even more so car roofs, is I think
often a degree or so lower than the air temperature though in clear
conditions, as they are radiating heat directly out into space. So if the
car owners are covering their cars with tarpaulins, they may have a point.
But Keith is talking about an air frost. If you have a grass minimum
thermometer you can report the ground temperature and so have a ground frost
when teh air temp is above zero. On clear calm nights this can be many
degrees below the air temp measured at ~4feet. On windy nights it will be
very similar to the air temp. Cars are not good places to shelter in a cold
calm night - they radiate faster than the ground does - as I think John is
saying.
I had an interesting one yesterday morning. The minimum air temp was +0.3C but
the garden pond was completely frozen over. There was a Force 2-3 breeze
blowing so I suspect that the surface of the pond cooled below 0C due to
evaporation. A good example of physics at work.

--
Norman Lynagh
Tideswell, Derbyshire
303m a.s.l.
https://peakdistrictweather.org
Twitter: @TideswellWeathr

It makes a massive difference coming out of the sea from a swim when it's windy, even more so when the humidity is low. You can really feel physics at work. If it's still, sunny and humid then 12C feels fine.

Looks like we'll finally get a single figure maximum tomorrow, though set to be far too windy for an air frost here for at least the next few days.

Near deserted out for a walk today, apparently everyone's in Truro, post lockdown Christmas shopping. I can't see the attraction at the best of times. Still it's good to see a bit of consumerism, after recent events global warming could do with a boost, also helped by the destruction of the rainforest is going better than ever https://inews.co.uk/news/environment...lsonaro-778271 . That battle is lost I'm afraid.

Still time to do something about plastic. You know, drink water from the tap rather than a plastic bottle, or milk from a glass bottle, or drink beer. Eat veg bought from a greengrocers not Tesmorburys, that isn't pumped full of CO2 & wrapped in plastic, that sort of thing.

Graham
Penzance