Jonathan Stott wrote:
Am I right in thinking that if the temperature is below freezing at 9am
(when observations for one day end) then it would count as two days with
air frost rather than one?

--
Jonathan Stott
Canterbury Weather: http://www.canterburyweather.co.uk/
Reverse my e-mail address to reply by e-mail

Hi, Jonathan,

If you are working to Met O climatological station rules of 24 hour,
09Z - 09Z obs, then that is correct. If you are working to 00Z - 00Z,
then the temperature at midnight would be the deciding factor, or 18Z -
18Z at 18Z and so on, depending on the obs hour.

It is a misleading reading, especially if the following night is mild,
as this one will be, but unavoidable at the majority of climatological
stations that are visited only once each day at 09Z. As far as the
record books go the coming night will have an air frost whatever
happens and the max for today will probably be at 09Z tomorrow morning
(thrown back)!

A more accurate 12 hour method is used at some synop. sites where the
max refers to 09Z - 21Z and the min 21Z - 09Z.

HTH

Ken Cook, Copley 253 metres asl, nr Barnard Castle, County Durham
http://mysite.wanadoo-members.co.uk/copley