Martin Rowley wrote:

"ronaldbutton" wrote in message
... snip
At present in my back garden the temp is 26C and the RH 55%,which with the
easterly breeze feels very comfortable ,so excuse my ignorance but how the
comfort levels determined viz a viz temperature combined with humidity ?.
I'd hate to enjoy myself whilst so many people seem to be struggling with
the dreadful heat and having to remove their anoraks.

... well, I'm probably way out of date now on all this as I know that a lot
of work has been done in the Met Office with the DoH & individual NHS trusts.
However, the standard algorithm we used to use to work out a
'temperature-humidity' index is as follows:-

THI = 0.4 (T + W) + 4.8 .... (for degC).

whe
THI 'Temperature/Humidity Index'
T = Dry bulb (screen) temperature
W = Wet bulb (screen) temperature

For THI 20, " increasing discomfort felt" [ for ' sedentary workers indoors
' or outside in shade in light winds ] THI = 24 .. half sample population
will feel 'discomfort'. THI 27 .. 'all' are likely to be distressed.

From your figures, I make your THI somewhere around 23.

As I say, things have no doubt moved on, but it should give a reasonable
guide.

The Met Office system here ...
http://www.metoffice.gov.uk/weather/...lth/index.html

appears only to be triggered by temperature, though given that night minima
are included (which in turn are governed by boundary-layer humidity), you
could argue that the humidity element is implicitly covered. I believe though
that in the US humidity is explicitly modelled in heat-stress warnings.


Martin.


The one that I've used for a long time is the so-called Humisery Index which is


Index = (((2Td) +T)/3)-12 (for deg C)

An index value of 0 is very comfortable for most people while an index of 10 is
extremely uncomfortable.

My 1500z obs gives an index of 7.9 which fits very well with how it feels.

I don't know where the Humisery Index came from. I was introduced to it by
Philip Eden many moons ago. I have half an idea that Philip actually devised
the index but I'm not sure. No doubt he will tell us.

--
Norman Lynagh
Tideswell, Derbyshire
303m a.s.l.