"Adrian D. Shaw" wrote in message
...

Can someone please explain the McKenzie method? I can't find it in the
FAQ.


.... it's on my 'to do' list, which is growing!

In essence, you take the day maximum (Tx) and the air-mass dew point
(Td), the latter is assumed not to change appreciably overnight.

Then T(min) = 1/2 (Tx + Td) - K

where K varies according to the expected surface wind speed and average
cloud overnight.

McKenzie originally did his work for Dyce (Aberdeen) and it was
presented (though not published) in 1944 in an internal memorandum
within the Meteorological Office. Since that time, constants for many
Met Office site have been calculated (Claude Kensett), but as a rough
guide:-

Dead calm/clear throughout night .. K =~ 8 or 9 (an extreme case)

Light wind/small amounts cloud .. K =~ 6 to 8
Light wind/cloud coming and going .. K =~ 4 or 5
Light wind/generally cloudy .. K =~ 2 or 3

Moderate wind/small amounts cloud .. K =~ 3 to 5
Moderate wind/cloud coming and going .. K =~ 3 or 4
Moderate wind/generally cloudy .. K =~1 or 2

Brisk winds (most cloud classes) .. K =~ 1 or 2

there are other corrections you can apply given the time of year etc.

You can see the beauty of the method, as it is easy to apply .. add
together a couple of commonly known variables, divide by 2, and then
fudge the 'correction' K.

Martin.